Newton's First Law of Motion:
I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

This we recognize as essentially Galileo's concept of inertia, and this is often termed simply the "Law of Inertia".

The law of inertia states that:
A body will preserve its velocity and direction so long as no force in its motion's direction acts on it.

Newton's Third Law of Motion:
III. For every action there is an equal and opposite reaction.

Hello,

Motion and rest are two prime considerations in any science/system. Every/most of the aspects may be dependent on these two concepts.

Can you tell me:-

Differance in forces required for bringing same object into motion and into rest?

Alike laws of motion, are/can there some law of rest?

Best wishes.

Laws of rest.... fascinating... i will ponder it.
-MT

Newon does have a law of rest - his first. A body at rest tends to stay at rest...

Rest is the absence of motion. There is a whole body of physics called "statics" that deals with forces applied-to/felt-by things at rest. A prime example of where this is used is structural members like roof trusses.

Under ideal conditions (i.e. absence of friction or losses - so perhaps floating in a vacuum) force required to say, accelerate a body to a certain speed would be the same scalar quantity (but applied in the opposite in direction) as the force required to bring it back to rest.

I think the important point here is inertia... I.e.. why is that to accelorate an object threw space requires the input of energy....
I.e.. if we apply energy to slow an object for example...
where did the energy go?

Can energy then be destroyed? and if so.. what does it become?

all of which suggests a missing component, which i would propose is the mystery of the physical relationship had between what we call matter and space.

i must ponder this.. likely for some time.
-MT (thankyou for mentioning it.)

Let me add:-

Motion
the act or an instance of changing position: an impulse or inclination of the mind or will

Motion
In physics, means a change in the position of a body with respect to time, as measured by a particular observer in a particular frame of reference.

Rest
1 freedom from activity or labor
2 a natural periodic loss of consciousness during which the body restores itself <after a long day, I lay down on the couch for a little rest before dinner>
Near Antonyms: pressure, strain, stress, tension
Antonyms: exertion, labor, toil, work

Rest(object)
A rest is an object used for supporting another, specific object, which is set to rest upon it (i.e. finding stability) and often diverts its weight to or by it.

Rest(physics)
Rest in physics and in the technical sense of geometric mensuration denotes a particular relation between a pair of observers.

Static exerting force by reason of weight alone without motion
: of or relating to bodies at rest or forces in equilibrium
: showing little change

Stable: marked by the ability to withstand stress without structural damage or distortion

Still: devoid of or abstaining from motion : free from storms or physical disturbance.

Stationary : fixed in a place or position: not undergoing a change in condition

Which of above is an true Antonyms of motion?

Whether an object require force/energy to remain in rest(or in antonyms of motion)?

Whether an object at rest tends to move toward motion in view of "Rest being a natural periodic loss of consciousness during which the body restores itself"?

Whether concept "rest" or any other antonyms of motion really exist on earth in view of earth remains in motion continiously and everything and being is also moving along with it? :p

I.e.. if we apply energy to slow an object for example...
where did the energy go?You have it a little backwards. If you slow an object down you get energy out of it. In other words, the object does work on whatever is slowing it. When you "apply energy" to an object you will always either increase its potential energy or speed. In that case the energy winds up as kinetic energy in the object itself.

-Dale

When an object in motion it/tool for its motion tends to loose energy and when at rest it may tend to gain/restore energy. (Rest: 2 a natural periodic loss of consciousness during which the body restores itself).

It may justfy third law of motion but how it can justify first law of motion or law of inertia?

Whether an object require force/energy to remain in rest(or in antonyms of motion)?You are correct that it often requires force for an object to remain at rest, but not energy. Energy is the capacity to do work which in turn is a force applied over a distance. So if an object is at rest then the distance is zero so the energy is also zero, regardless of the forces involved.

This concept is particularly misunderstood for magnets. No more energy is being expended to keep a magnet at rest on your refridgerator than is expended to keep your monitor at rest on your desk.

Whether concept "rest" or any other antonyms of motion really exist on earth in view of earth remains in motion continiously and everything and being is also moving along with it? :pYou can always define a given object to be at rest by judicious choice of the coordinate system. However, if you choose a non-inertial coordinate system, then you will have to include some ficticious forces (http://en.wikipedia.org/wiki/Fictitious_force) in order to account for your accelerating coordinate system. The biggest of these ficticions forces in an earth-based coordinate system would be the Coriolis force (http://en.wikipedia.org/wiki/Coriolis_force). As long as the magnitude of this force is sufficiently small then you can treat your coordinate system as approximately inertial. This is a good approximation in most "everyday life" physics problems, but a bad approximation in meterology.

You are correct in noting that there is no truly inertial reference frame with objects on the earth being at rest. That is not really surprising considering that objects on earth are constantly experiencing forces. The forces are always slightly unbalanced leading to some acceleration relative to any inertial frame according to Newton's laws.

-Dale

When an object in motion it/tool for its motion tends to loose energy and when at rest it may tend to gain/restore energy. (Rest: 2 a natural periodic loss of consciousness during which the body restores itself).

It may justfy third law of motion but how it can justify first law of motion or law of inertia?First, don't use that definition for rest in a physics problem since it is pretty useless to speak of objects having consciousness.

Second, I don't think you understand the history here. In classical physics Newton's laws are the first principles. The concept of energy was derived from Newton's laws, so you cannot use energy concepts to justify Newton's laws since it would be circular logic. As far as I know Newton's laws are not justified in any theoretical sense, they are only justified empirically. In other words, they fit the facts so well (in non-relativistic limits) that there is little reason to doubt them.

-Dale

Every motion, every movement in the universe is a means towards peace, towards equilibrium, absence of motion. Evolution is to become oneself. If I were already myself, I would not evolve, I would be at peace. But it's because I refuse myself, my nothingness, that I feel myself 'being' and subsequently am bound to become what I am.

You are correct that it often requires force for an object to remain at rest, but not energy. Energy is the capacity to do work which in turn is a force applied over a distance. So if an object is at rest then the distance is zero so the energy is also zero, regardless of the forces involved.This concept is particularly misunderstood for magnets. No more energy is being expended to keep a magnet at rest on your refridgerator than is expended to keep your monitor at rest on your desk.

We/object travel a distance with earth's movement even at rest.:) Thanks.



You can always define a given object to be at rest by judicious choice of the coordinate system. However, if you choose a non-inertial coordinate system, then you will have to include some ficticious forces (http://en.wikipedia.org/wiki/Fictitious_force) in order to account for your accelerating coordinate system. The biggest of these ficticions forces in an earth-based coordinate system would be the Coriolis force (http://en.wikipedia.org/wiki/Coriolis_force). As long as the magnitude of this force is sufficiently small then you can treat your coordinate system as approximately inertial. This is a good approximation in most "everyday life" physics problems, but a bad approximation in meterology.

You are correct in noting that there is no truly inertial reference frame with objects on the earth being at rest. That is not really surprising considering that objects on earth are constantly experiencing forces. The forces are always slightly unbalanced leading to some acceleration relative to any inertial frame according to Newton's laws.

-Dale

Sorry, I am bit non-technical. How newton's first and third law of motion apply to an object in motion and at rest(still at motion?)?

Every motion, every movement in the universe is a means towards peace, towards equilibrium, absence of motion. Evolution is to become oneself. If I were already myself, I would not evolve, I would be at peace. But it's because I refuse myself, my nothingness, that I feel myself 'being' and subsequently am bound to become what I am.

It is spritual or science's thought? Although may be logical fact, a definition of "salvation" or a definition of nature's balance/homeostatis, but I don't know how it can e possible? It somewhat tells, if prime force of all forces is there, it may be a peace/rest or balance uneffected by any motion.:) OK? :o

Sorry, I am bit non-technical. How newton's first and third law of motion apply to an object in motion and at rest(still at motion?)?I am not sure that I understand your question. I think you are asking about how you can apply Newton's laws in a non-inertial reference frame. If so, please check out the links I provided earlier (http://en.wikipedia.org/wiki/Fictitious_force and http://en.wikipedia.org/wiki/Coriolis_force).

Basically, Newton's laws work just like normal except that you must include a fictitious force. This fictitious force does not really exist (that is why it is called fictitious), but it is necessary in order to explain the motion of objects in the non-inertial coordinate system. I believe that ficticious forces can be distinguished from real forces by Newton's 3rd law, i.e. there is no "equal and opposite" reaction force to a ficticious force, instead it is purely an artifact of the coordinate system.

If I missed the point of your question please try to rephrase it in more detail.

-Dale

It is spritual or science's thought? Although may be logical fact, a definition of "salvation" or a definition of nature's balance/homeostatis, but I don't know how it can e possible? It somewhat tells, if prime force of all forces is there, it may be a peace/rest or balance uneffected by any motion.:) OK? :oIt is not a scientific thought at all. It is pretty weak as far as spiritual thoughts go, IMO.

-Dale

Basically, Newton's laws work just like normal except that you must include a fictitious force. This fictitious force does not really exist (that is why it is called fictitious), but it is necessary in order to explain the motion of objects in the non-inertial coordinate system. I believe that ficticious forces can be distinguished from real forces by Newton's 3rd law, i.e. there is no "equal and opposite" reaction force to a ficticious force, instead it is purely an artifact of the coordinate system.

-Dale[/QUOTE]

How fictitious force does not really exists? Are these not considered as fictitious for the sake of understanding apparent motion by keeping earth's motion's effects as standard?

Anyway, When two exactly similar objects move in opposite directions with same force/energy--one in line of earths revolution and other opposite to it. What can be the difference in their motion?

Can different times and other plannet's influences at different times, effect the movements or rest (vibrations) of an object? For deeper thought--can this effect vibrations in atomic and molecular structures of an object?

Basically, Newton's laws work just like normal except that you must include a fictitious force. This fictitious force does not really exist (that is why it is called fictitious), but it is necessary in order to explain the motion of objects in the non-inertial coordinate system. I believe that ficticious forces can be distinguished from real forces by Newton's 3rd law, i.e. there is no "equal and opposite" reaction force to a ficticious force, instead it is purely an artifact of the coordinate system.

-Dale

How fictitious force does not really exists? Are these not considered as fictitious for the sake of understanding apparent motion by keeping earth's motion's effects as standard?

Anyway, When two exactly similar objects move in opposite directions with same force/energy--one in line of earths revolution and other opposite to it. What can be the difference in their motion?

When two similar objects are at rest at two different places on earth, can there be some difference in naturally applied forces on them and in vibrations within them?

Can two adjunt objects at rest interfere/effect each other at naturally applied forces and so vibrations in them?

Can different times and other plannet's influences at different times, effect the movements or rest (vibrations) of an object? For deeper thought--can this effect vibrations in atomic and molecular structures of an object?

It looks that every object can't be at complete/true rest/peace at any time on earth (may be within solar system) due to plannetary movements...and always experiance some vibrations (vibrations in atoms and molecules).

Do plannetary movements cause and maintain these movements/vibrations and influence of gravity and sun resist these movements/vibrations?

>> can there some law of rest?

The Inertial State as per Newton's laws is confusing....
because no body in the Universe can be static (without motion), and all motion is in a curve (a straight line path can not exist )

so that law coined way back then has to be modified

So what is an inertial state ?

The only inertial state I have identified is exhibited by a cosmic body in circular orbit around a centre of spin....

Venus is very close to an inertial state..... this planet can be considered as "at rest" or inertial......it exhibits perpetual motion where all forces are in equilibrium...

Just to really confuse the issues RE: Laws of Rest

An inertial body is alway being accelerated...... it is under constant acceleration as it orbits the centre of spin.

so a good definition of inertia is

Matter that has constant velocity under constant acceleration is inertial.

This negates Einstein's claim that a body falling with gravity is 'inertial'.

>> can there some law of rest?

The Inertial State as per Newton's laws is confusing....
because no body in the Universe can be static (without motion), and all motion is in a curve (a straight line path can not exist )

so that law coined way back then has to be modified

So what is an inertial state ?

The only inertial state I have identified is exhibited by a cosmic body in circular orbit around a centre of spin....

Venus is very close to an inertial state..... this planet can be considered as "at rest" or inertial......it exhibits perpetual motion where all forces are in equilibrium...

Good thought.

unquote:
{Spritually venus is related to Goddess and goddess to force/energy.:}

What about Sun?

Can Sun and gravity can be considered as "rest causing entities".

Motion and rest are two prime aspects--may be a cause of everything. Earth's and plannetry's movements as cause of motion and gravity and sun as a cause to rest. Is it ok?

Whether an object tends to change its position in view of above influences...towards rest when in motion AND towards motion when at rest? Contractions & relaxations, hot & cold, day & night, dry and moist...may be relevant to motion and rest.(pendulum?)

The only inertial state I have identified is exhibited by a cosmic body in circular orbit around a centre of spin....

Can it be axis?

How fictitious force does not really exists? Are these not considered as fictitious for the sake of understanding apparent motion by keeping earth's motion's effects as standard?

Anyway, When two exactly similar objects move in opposite directions with same force/energy--one in line of earths revolution and other opposite to it. What can be the difference in their motion? So that we can get rid of the effects of planetary motion, solar motion, galactic motion, etc. let's consider a simpler case. Imagine we have an inertial observer that is stationary in an inertial frame in deep space. Near this observer is a large cylindrical space station which is rotating about its axis of symmetry which coincides with the z axis of the inertial frame, the station is not otherwise moving in the inertial frame. Inside the station is a non-inertial observer, he is standing on the inside surface of the space station and is experiencing a gravity-like centripetal acceleration. For convenience, this second observer uses a non-inertial reference frame, the axis of the space station he calls North-South and the station rotates towards the East with East being on his right as he looks North. The non-inertial observer throws a ball due North, the inertial observer sees that the ball travels in a straight line after it leaves the non-inertial observer's hand and the space station rotates around the path of the ball. In the non-inertial frame, however, the second observer sees that after the ball leaves his hand it is deflected to the West (left). The non-inertial observer repeats his experiment but throws the ball to the South this time and observs that it is deflected to the West (right). In order to explain this behaviour he invents a ficticious force pointing to the West. The inertial observer needs no such ficticious force in order to characterize the motion of the ball.

The same concept applies on Earth. The rotation of the Earth about it's axis provides an equivalent westward deflection as an object is thrown towards the equator. This force is incredibly small relative to the other forces on a person throwing a ball, but it is large relative to the other forces on a cloud. Effects from the Earth's orbit around the sun and the sun's orbit around the galactic center are positively miniscule as are the forces due to other planets. They are there, but they are so tiny that the gentlest breeze or a small seismic tremor thousands of miles away are much greater effects.

-Hope that helps
Dale

It looks that every object can't be at complete/true rest/peace at any time on earth (may be within solar system) due to plannetary movements...and always experiance some vibrations (vibrations in atoms and molecules).

Do plannetary movements cause and maintain these movements/vibrations and influence of gravity and sun resist these movements/vibrations?The planetary movements do cause and maintain these "vibrations", but nothing resists them. They are just insignificantly small. These are in no way the same as the vibrations in atoms and molecules that are associated with thermal energy. Thermal vibrations result in no bulk motion while these planetary vibrations do. Also, the planetary vibrations would not cause heat whereas the atomic vibrations essentially are heat.

To get an idea about how insignificant these vibrations are you should actually do the calculation for the largest planet, Jupiter (http://en.wikipedia.org/wiki/Jupiter). This will be much smaller than the Coriolis effect which is already negligible for most cases.

-Dale

so that law coined way back then has to be modifiedYes. That is the whole point of SR and GR. It is well recognized. However, in everyday life (non-relativistic limits) Newton's laws work very well.

-Dale

so a good definition of inertia is

Matter that has constant velocity under constant acceleration is inertial.

This negates Einstein's claim that a body falling with gravity is 'inertial'.Stop spouting nonsense. That is a terrible definition of anything because it is mathematically impossible (a=dv/dt -> v = a t + v0 is not a constant velocity for a constant acceleration). It negates nothing except your own credibility.

-Dale

Good thought.

unquote:
{Spritually venus is related to Goddess and goddess to force/energy.:}
I get the impression that I am trying to talk science to someone who wants to hear pseudoscience or perhaps mysticism. Feel free to chant whatever mystical mumbo-jumbo you wish, there are plenty on this forum who will indulge you. Just realize that you are leaving science for fantasy.

-Dale

This means that the source of energy is not an origin in the past but an aim in the future. There is no energy in the past. It does not exist. All energy comes from unity, nothingness, infinity, the goal, which is here in the present moment, which can't be seen because it has no duration, which is the field of causes and not of visible past effects...

The nothingness, with its "existence", gives energy to this world... it is the only thing that really exists.

Feel free to chant whatever mystical mumbo-jumbo you wish, there are plenty on this forum who will indulge you. Just realize that you are leaving science for fantasy.

This means that the source of energy is not an origin in the past but an aim in the future. There is no energy in the past. It does not exist. All energy comes from unity, nothingness, infinity, the goal, which is here in the present moment, which can't be seen because it has no duration, which is the field of causes and not of visible past effects...

The nothingness, with its "existence", gives energy to this world... it is the only thing that really exists.
case in point

-Dale

DaleSpam,

Pls tell those forces which try to make us in motion and at rest? I assumed earth's motion and sun/gravity respectively. ??

>> Newton's laws work very well.

the Laws, are archaic
but Newtonian mechanics rocks.

You didn't understand a word I posted , did you Dale ?

Pls tell those forces which try to make us in motion and at rest?
Magnetism.

Pls tell those forces which try to make us in motion and at rest? I assumed earth's motion and sun/gravity respectively. ??Any force acting on a body, by itself, will cause an acceleration. It doesn't matter if the force is from gravity, electromagnetic fields, contact, etc.

-Dale

the Laws, are archaic
but Newtonian mechanics rocks.You speak as though Newtonian mecnanics were independent of Newton's laws of motion. The mechanics do not exist without the laws.
You didn't understand a word I posted , did you Dale ?I understood. Your definition of inertia was just blatantly impossible.

-Dale

by DaleSpam:

Inside the station is a non-inertial observer, he is standing on the inside surface of the space station and is experiencing a gravity-like centripetal acceleration.
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Your example is confusing, Dale. To begin with, centrifugal force is the center fleeing force. Centripetal force is the center SEEKING force. The centripetal force is felt as the pressure against the second observer's feet, forcing his change of direction. The
centrifugal force is the force that causes the acceleration away from the center of the rotating cylinder. However, the second observer is not accelerating WITHIN the cylinder as the two forces are of equal magnitude and balance out. The ball would feel an acceleration due to centrifugal force until it rests against the cylinder wall, at which point the two forces would cancel ending the acceleration.
---------------------------------------------------------------------------------

by DaleSpam:

The non-inertial observer throws a ball due North, the inertial observer sees that the ball travels in a straight line after it leaves the non-inertial observer's hand and the space station rotates around the path of the ball.
================================================== ===========

The non-inertial observer would see the ball travel in a straight line ONLY if the ball were released along the central axis of the cylinder, in which case both observers would see the ball travel in a straight line, the centrifugal force is balanced in both lateral directions. If the ball were released closer to one wall of the cylinder than the other wall, the ball would feel a centrifugal force directed away from the center of the cylinder. The non-inertial observer inside the rotating cylinder would see the path of the ball curve towards the wall of the cylinder in line with his location wrt the wall. The inertial observer, assuming the cylinder was transparent, would see the ball travel a widening corkscrew pattern as the ball rotated with the cylinder and approached the wall. Special Theory does not correctly explain the motions due to the acceleration of the ball as it is travelling.

Your example is confusing, Dale. My apologies. It was the best I could come up with on the spur of the moment. I chose the space station example because I wanted to eliminate gravity and orbital motion as confounding factors. I was trying to show ficticious forces in as "pure" an example as I could concoct. I would be glad for a better example.

To begin with, centrifugal force is the center fleeing force. Centripetal force is the center SEEKING force. The centripetal force is felt as the pressure against the second observer's feet, forcing his change of direction.Precisely. That is what I meant by a gravity-like centripetal acceleration. The non-inertial observer feels the centripetal acceleration as his feet push against the floor in the same way that I feel gravity as my feet push against the ground.

You are right! I definitely should have talked about the centrifugal force. It is not a real force, it is a ficticious force that only exists in the non-inertial frame. In fact it is the single most important ficticious force in any rotating frame. The Coriolis force that I was describing is typically much smaller. I guess that I just got so used to never talking about the centrifugal force that I neglected to mention it when it actually was appropriate.

The inertial observer, assuming the cylinder was transparent, would see the ball travel a widening corkscrew pattern as the ball rotated with the cylinder and approached the wall.I think this is slightly inaccurate. Here you are considering (in the non-inertial frame) only the centrifugal force and not the Coriolis force as well. The inertial observer definitely sees the ball travel in a straight line since there are no real forces acting on the ball. The non-inertial observer has to use two ficticious forces, the centrifugal force and the Coriolis force to account for the motion in the rotating frame. The centrifugal force describes the motion "down" in the rotating frame while the Coriolis force describes the deflection to the "west" in the rotating frame.

I appreciate your input. I really could have simplified the explanation by only talking about the centrifugal force. I wouldn't have even needed to use a dropped or thrown ball, just the non-inertial observer's experience of "weight". The Coriolis force just adds an unnecessary layer of complexity.

-Dale

>> Matter that has constant velocity under constant acceleration is inertial. >>

I am talking of cosmic situations here. No matter on Earth can be considered truely inertial.
However Newton's law is adequate for Earth situations, even though it is inadequate (limited).

Inertia
A planet in circular [inertial] orbit has constant angular acceleration, and that produces a constant tangential velocity. This situation is paramount for celestial bodies.... non circular orbits are harmonic variations of the circular [inertial] orbit.

>> Matter that has constant velocity under constant acceleration is inertial. >>

I am talking of cosmic situations here.It is unimportant wether you are talking about cosmic situations or terrestrial situations. Acceleration is the time derivative of velocity (i.e. a = dv/dt). If you have a constant acceleration then you have a linear velocity (i.e. v = a t + v0). It's not a question of the situation it is a question of the relationship between velocity and acceleration. Under constant acceleration you will always have a linear velocity, it doesn't even have anything to do with matter or inertia. You can talk just as well about an accelerating coordinate system.

A planet in circular [inertial] orbit has constant angular acceleration, and that produces a constant tangential velocity.I don't think you really want to talk about angular acceleration and tangential velocities because the angular acceleration is zero for a circular orbit. In any case, neither the acceleration nor the velocity are constant for a circular orbit, or any other uniform circular motion.

-Dale

Magnetism.

Tell me what makes object to rest.

Any force acting on a body, by itself, will cause an acceleration. It doesn't matter if the force is from gravity, electromagnetic fields, contact, etc.

-Dale

What can then make a body to come into real/complete state of rest? What can stop vibrations in a body? When two different poles of two similar magnets came into contact--doet it causes vibrations within magnet to come into rest and opposite when they repel each other?

Actually, in humans contractions and relaxations are two prime mechanisms. Probably we have studied mostly contraced conditions but relaxed conditions can be equally important. It is also indicative that people with prominent relaxed conditions tends to remain more active physically(probably try to come into motion--opposite reaction) and people with prominient contracted conditions tend to remain lazy physically. It think, it tells that newton's third law of motion is applicable on terrestrial stiuations but may not be in cosmic ...where first law may be more applicable. It looks things tends to behave oppsite to their current position/condition in terrestrial stiuations. Indicative, but I don't know how can I explain it for non living things ???

>> Under constant acceleration you will always have a linear velocity

indeed, but the linear velocity will not be constant.

What can then make a body to come into real/complete state of rest? What can stop vibrations in a body?If there were no forces acting on a body then there would be an inertial frame where the body would be at rest. This inertial frame is sometimes called the rest frame.

As far as stopping the vibrations in a body, since the vibrations are essentially thermal energy, you would have to cool the body to absolute zero (http://en.wikipedia.org/wiki/Absolute_zero). This has never been achieved, and I am not sure if it is even theoretically possible from a thermodynamics standpoint.

It think, it tells that newton's third law of motion is applicable on terrestrial stiuations but may not be in cosmic ...where first law may be more applicable. Newton's first two laws and his third law are both applicable in any non-relativistic situation, cosmic or terrestrial. The first two laws describe the effect of forces on one body. The third law describes the interaction of two bodies. In other words, the first two laws say that the acceleration of a body is proportional to the force on that body. The third law says that if body A exerts a force on body B then body B exerts an equal and opposite "reaction" force on body A.

-Dale

by DaleSpam:

Precisely. That is what I meant by a gravity-like centripetal acceleration. The non-inertial observer feels the centripetal acceleration as his feet push against the floor in the same way that I feel gravity as my feet push against the ground.
================================================== ============

I have a couple of minor points to your post. On the surface of the Earth, the force due to gravity is a centripetal-like force, directed towards the center of the Earth. In the rotating cylinder, the acceleration is away from the center of the cylinder, a centrifugal force. The acceleration of the observer in the cylinder is due to CENTRIFUGAL force, not centipetal force. The centipetal force is the walls of the cylinder pushing against the observer's feet, to stop the observer's outward motion (his acceleration). You were correct that I neglected the coriolis force, caused by the
ball retaining its initial velocity at the point of release and then moving outward toward the relatively faster rotating cylinder walls.
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by DaleSpam:

The inertial observer definitely sees the ball travel in a straight line since there are no real forces acting on the ball.
================================================== ============

This is my point of disagreement. Whether relativity considers the forces as 'real forces' or 'pseudo forces', the effects are still there. The ball does not travel in a straight line, to either the non-inertial observer nor the inertial observer. The ball will curve in its trajectory due to both the centrifugal force and the coriolis force. An observer at rest in an inertial frame MUST see the ball trajectory curve toward the outside wall of the cylinder, all the while both the cylinder and ball are also rotating.
This was my 'widening corkscrew' motion. Do you disagree?

indeed, but the linear velocity will not be constant.Yes, you got it exactly! If acceleration is constant then v = a t + v0 is not constant.

-Dale

On the surface of the Earth, the force due to gravity is a centripetal-like force, directed towards the center of the Earth. In the rotating cylinder, the acceleration is away from the center of the cylinder, a centrifugal force. The acceleration of the observer in the cylinder is due to CENTRIFUGAL force, not centipetal force. The centipetal force is the walls of the cylinder pushing against the observer's feet, to stop the observer's outward motion (his acceleration). I think I can agree with that. The obvious difference is that you stand on the inside of the space station and on the outside of the earth. There are two commonly used meanings for centrifugal force (http://en.wikipedia.org/wiki/Centrifugal_force) one refers to the fictional force in the rotating frame and the other refers to the real outward-pulling reaction force. I was exclusively using the meaning of a fictional force in the rotating frame. In that frame the non-inertial observer definitely feels the centrifugal force pulling "down". I am not 100% sure which meaning you have been using.

This is my point of disagreement. Whether relativity considers the forces as 'real forces' or 'pseudo forces', the effects are still there. The ball does not travel in a straight line, to either the non-inertial observer nor the inertial observer. The ball will curve in its trajectory due to both the centrifugal force and the coriolis force. An observer at rest in an inertial frame MUST see the ball trajectory curve toward the outside wall of the cylinder, all the while both the cylinder and ball are also rotating.
This was my 'widening corkscrew' motion. Do you disagree?Yes, I disagree, but I can't think of a way to show it other than simulation and, of course, if I wrote the simulation it wouldn't be very convincing to you :D (also I don't think we need to involve any SR corrections here, I am not trying to talk about a rotating space station with a tangential velocity that is a sizeable fraction of c)

Instead of talking about a thrown ball, let's simplify the situation by having the non-inertial observer just drop the ball. Do you still think it would corkscrew there? I don't. I think the inertial observer would see the ball travel in a straight line with a velocity equal to the tangential velocity at the moment of release. In the inertial frame the fictional-force version of centrifugal force does not exist at all, and the reaction-force version of centrifugal force ceases as soon as the ball is dropped. So in the inertial frame there is no centrifugal force of either kind to cause the ball to deviate from a straight line path.

I think that if the ball were to travel in a corkscrew path in the inertial frame then Newton's laws would be wrong. If there are no forces acting on the ball and it does not travel in a straight line then F != m a. But again, I don't know how to show it other than simulation.

-Dale

Do you want to say that gravity/earth forces are alike tornado/whirlpool type effect?

How newtons third law can be applicable in cosmic stiuations?

Think of clothes drying inside a commercial clothes dryer, the kind with the glass door.
if the observer is standing at the end of the cylinder, or in front of the clothes dryer, he will see the wet clothes thrown to the outside wall of the clothes dryer due to centrifugal force. A ball initially that is initially resting on top of a pile of clothes near the center axis of the dryer will migrate closer to the wall of the dryer due to centrifugal force. The observer standing in front of the dryer will see the ball move in a widening spiral as it rotates with the dryer. If the ball also had motion toward or away from the outside observer, the motion would appear as a widening corkscrew-type trajectory. Maybe you are positioning your inertial observer in a different location, such as watching a farris wheel from the perimeter of the wheel. In such a viewing location wrt your rotating cylinder, the pitched ball would appear as a corkscrew motion moving from his left to right or vice versa. A dropped ball would appear as a widening spiral viewed edge-on. The motions are the same on Earth as in space, unless the Earth examples are rotating slow enough to allow gravity to overcome the centrifugal force. These examples are also ignoring the coriolis force. If
your outside observer were rotating with the cylinder in the space-based example (kind of a geostationary orbit), he would not be in an inertial frame without the centripetal force of gravity to balance his centrifugal acceleration, such as an object orbiting a gravitating body would feel no acceleration.

If there were no forces acting on a body then there would be an inertial frame where the body would be at rest. This inertial frame is sometimes called the rest frame.

As far as stopping the vibrations in a body, since the vibrations are essentially thermal energy, you would have to cool the body to absolute zero (http://en.wikipedia.org/wiki/Absolute_zero). This has never been achieved, and I am not sure if it is even theoretically possible from a thermodynamics standpoint.

Does it mean that there can't be absolute rest but just variations in motions can only be there and rest so commonly called is just "a comparative lesser motion in comparsion to higher motion" alike a seated person in running train? Ok?



Newton's first two laws and his third law are both applicable in any non-relativistic situation, cosmic or terrestrial. The first two laws describe the effect of forces on one body. The third law describes the interaction of two bodies. In other words, the first two laws say that the acceleration of a body is proportional to the force on that body. The third law says that if body A exerts a force on body B then body B exerts an equal and opposite "reaction" force on body A.

-Dale

How an opposite "reaction" is intiated/exerted by body B? What is the science of reaction?

"In physics, a reaction is defined by Newton's third law: "For every action there is an equal and opposite reaction". The idea that any given force has a pair or opposite force.
Usually, a reaction is any response caused by some other action. The idea that any given force has a pair or opposite force." http://en.wikipedia.org/wiki/Reaction

I think above definition don't clear the science of reaction?

By the way, DaleSpam, I just looked at your link to the Wikipedia site. I do not think it is very clear. Here is a better link to the HyperPhysics site. It has a clearer explaination of all three of the forces with diagrams, coriolis, centrifugal and centripetal.
http://hyperphysics.phy-astr.gsu.edu/hbase/corf.html

Also, a NASA astronaut conducted a basic experiment with a toy car on a circular track aboard a space shuttle in orbit:
http://observe.arc.nasa.gov/nasa/exhibits/toys_space/fact_car_3.html

If there were no forces acting on a body then there would be an inertial frame where the body would be at rest. This inertial frame is sometimes called the rest frame.

As far as stopping the vibrations in a body, since the vibrations are essentially thermal energy, you would have to cool the body to absolute zero (http://en.wikipedia.org/wiki/Absolute_zero). This has never been achieved, and I am not sure if it is even theoretically possible from a thermodynamics standpoint.

Many terms are relavent.Zero-point energyhttp://en.wikipedia.org/wiki/Zero-point_energy ,Ground state: In physics, the ground state of a quantum mechanical system is its lowest-energy state http://en.wikipedia.org/wiki/Ground_state

Philosophy of conservation laws tells that:

"Things that remain unchanged, in the midst of change"

It somewhat indicates tendencies of changes/motions towards unchange/rest. Does it indicate that all motions/vibrations tends to change towards absolute zero tempereture or Zero-point energy or rest frame.






Newton's first two laws and his third law are both applicable in any non-relativistic situation, cosmic or terrestrial. The first two laws describe the effect of forces on one body. The third law describes the interaction of two bodies. In other words, the first two laws say that the acceleration of a body is proportional to the force on that body. The third law says that if body A exerts a force on body B then body B exerts an equal and opposite "reaction" force on body A.

-Dale

How can you relate it to attractions and repulsions?

By the way, DaleSpam, I just looked at your link to the Wikipedia site. I do not think it is very clear. Here is a better link to the HyperPhysics site. It has a clearer explaination of all three of the forces with diagrams, coriolis, centrifugal and centripetal.
http://hyperphysics.phy-astr.gsu.edu/hbase/corf.htmlYes, the hyperphysics example is clearer. The hyperphisics site only uses the fictional-force (effective force) version of a centrifugal force, not the reaction-force version. Thanks for the link.

-Dale

Do you want to say that gravity/earth forces are alike tornado/whirlpool type effect?No. I want to say that the earth is a non-inertial frame, but if the centrifugal and Coriolis forces are small enough to ignore then you can effectively consider it to be inertial (with gravity). This is a good approximation for every day life, but not for storms.

How newtons third law can be applicable in cosmic stiuations?If galaxy A exerts a gravitational force on galaxy B then galaxy B exerts an equal and opposite gravitational force on galaxy A.

-Dale

Does it mean that there can't be absolute rest but just variations in motions can only be there and rest so commonly called is just "a comparative lesser motion in comparsion to higher motion" alike a seated person in running train? Ok?You could say it that way if you wanted to, but I think that the modern view is a little more interesting. Lets say that the "train" travels through deep space and it passes through a deep-space "train station" without slowing. There are two passengers, one on the train and one in the station waiting for the next train. There are no forces acting on either one. If they close their eyes neither one has any indication of movement. No experiment they can perform can detect their own motion. They can therefore both claim that they are at rest. If they open their eyes they see other objects moving. They can therefore each claim that the other is not at rest. They are both right.

How an opposite "reaction" is intiated/exerted by body B? What is the science of reaction?By the same mechanism as body A. So if A is exerting an electrostatic force on B then B is exerting an equal and opposite electrostatic force on A. If the floor is pushing up on my feet with a contact force of 150 lbs then my feet are pushing down on the floor with a contact force of 150 lbs.

-Dale

Many terms are relavent.Zero-point energyhttp://en.wikipedia.org/wiki/Zero-point_energy ,Ground state: In physics, the ground state of a quantum mechanical system is its lowest-energy state http://en.wikipedia.org/wiki/Ground_state Unfortunately I do not know enough QM to talk about zero-point energy. You should probably not try to jump into QM until you get a much firmer grasp on classical mechanics.

Philosophy of conservation laws tells that:

"Things that remain unchanged, in the midst of change"

It somewhat indicates tendencies of changes/motions towards unchange/rest. Does it indicate that all motions/vibrations tends to change towards absolute zero tempereture or Zero-point energy or rest frame.No, you completely misuderstand conservation. In fact, things would only tend towards absolute zero if thermal energy were continuously lost rather than conserved.

How can you relate it to attractions and repulsions?If A is to the left of B and both A and B are positively charged then there will be repulsion. A will exert a force on B pointed right and B will exert an equal force on A but pointed left. The force on A acts to accelerate A away from B and the force on B acts to accelerate B away from A. That is what repulsion is.

-Dale

...How an opposite "reaction" is intiated/exerted by body B? What is the science of reaction?
"In physics, a reaction is defined by Newton's third law: "For every action there is an equal and opposite reaction". The idea that any given force has a pair or opposite force. Usually, a reaction is any response caused by some other action. ...Terms used in physics often have more limited and precise definitions than the same terms in general use. For example: "I have to go to WORK." That "work" has nothing to do with the product of a force and the distance thru which the force is applied.

The same is true of "reaction." In general use, "reaction" carries with it the "cause and effect" relationship, but not in physics. When A applies a force to B, B applies an "equal and opposite force to A." as you stated in the third law. Which you want to call the "action" and which you want to call the "reaction" is arbitrary, but humans do tend to have biases in their choices. For example, I would tend to say that the car's tires apply a force to the road and in reaction the road pushes the car forward, but it could just as well be the other way round - the road applies a force to the car, moving it forward and a reaction force is applied to the Earth by the tires. (The torque associated with this reaction force changes the Earth's spin a little, if it is not just overcoming the air resistence, but is accelerating the car.)

Perhaps the most useful application of "re-action/action" concept is it permits one to recognize as false some common forces. For example the force you feel when your car takes a "hair-pin" curve too fast, is not a force at all. We call this false force the "centrifugal force" but it does not exist in physics. It is not balancing out the real force the car seat is applying to you. You are accelerating towards the current center of curvature of the car's path and need an unbalanced force to do so. The "centrifugal force" has no "equal and opposite force." It is not a violation of the third law because it is not a force in the sense physics uses the word “force.”.

Yes, you experience a "centrifugal force" but it is not one of physic's forces. It is more like the "work" you do in the office - something of common experience that happens, unfortunately, to be called by the same term that physics uses to describe a well defined physical term, FORCE.

Tell me what makes object to rest.
Nothing rests in the world, but magnetism tries to make rest. Absolute rest would be non-existence.

Nothing rests in the world, but magnetism tries to make rest. Absolute rest would be non-existence.Does c7ityi = url? SAME SORT OF NONSENSE, makes me think so.

What about perfect crystal having absolute zero energy? Although perfect crystan is not there but it is not temp. dependent.

Nothing rests in the world, but magnetism tries to make rest. Absolute rest would be non-existence.

How?

No, you completely misuderstand conservation. In fact, things would only tend towards absolute zero if thermal energy were continuously lost rather than conserved.

If A is to the left of B and both A and B are positively charged then there will be repulsion. A will exert a force on B pointed right and B will exert an equal force on A but pointed left. The force on A acts to accelerate A away from B and the force on B acts to accelerate B away from A. That is what repulsion is.

-Dale
What about when two magnets attract or two magnets stick together by opposite pole or an iron piece stick to the magnet? Does it effect motions within magnet and iron piece?

Billy T, can you explain the difference between the 'gravitational force' and centrifugal force? Does the gravitational force have an equal and opposite force? The car seat and door exerts an equal and opposite reaction on the driver to offset the acceleration of the centrifugal force. The surface of the Earth exerts an equal and opposite reaction to offset the acceleration of gravity. Without the reactionary force of the car door or the Earth surface, neither the car driver nor the person standing on Earth would feel either force. So, why is gravity considered a 'real' force and centrifugal force considered a 'false' force? Both are due to a 'property' of mass, correct? Yes, I have known for a long time that relativity treats the centrifugal force as a 'false' force, but NASA and Newtonian Orbital Mechanics for instance, don't. I can
find a reference from NASA if you need one, I have read it several times before.

What about when two magnets attract or two magnets stick together by opposite pole or an iron piece stick to the magnet? Does it effect motions within magnet and iron piece?There is nothing special about magnets, they obey Newton's laws just like everything else.

If you mean what happens on a microscopic level then as a first approximation just consider that all the atoms in a piece of iron are like microscopic bar magnets. Normally they are all randomly oriented with no net magnetization, but in the presence of a strong magnet they align to produce a net magnetization and hence the magnetic force. This alignment really has very little to do with thermal motions and vibrations.

-Dale

How?

1. "Nothing rests in the world,"

All seemingly solid matter is full of atomic motion.

2. "but magnetism tries to make rest. Absolute rest would be non-existence."

Magnetism attracts things, it makes things unite, so that they would fall into singularity, nothingness. The earth has a magnetic attraction. The source of that power tries to unite with the earth (the repulsive force). It cannot do it because the resistance of matter is more powerful. But imagine that the resistance of matter would weaken, or that the attraction of the earth would become stronger than the repulsive power in matter: the matter would fall into a singularity and nothingness would take their place.

Everything that is visible is visible only because of its "motion" or "vibration".

Rest means balance. Mix black and white colors and they will both stop to exist, and gray will take their place which is both black and white (neither black or white). Gray represents "non-existence" on color level, since it has no opposite color.

Billy T, can you (1)explain the difference between the 'gravitational force' and centrifugal force? (2)Does the gravitational force have an equal and opposite force? (3)The car seat and door exerts an equal and opposite reaction on the driver to offset the acceleration of the centrifugal force. (4)The surface of the Earth exerts an equal and opposite reaction to offset the acceleration of gravity. (5)Without the reactionary force of the car door or the Earth surface, neither the car driver nor the person standing on Earth would feel either force. (6)So, why is gravity considered a 'real' force and centrifugal force considered a 'false' force? (7)Both are due to a 'property' of mass, correct? (8)Yes, I have known for a long time that relativity treats the centrifugal force as a 'false' force, but NASA and Newtonian Orbital Mechanics for instance, don't. I can find a reference from NASA if you need one, I have read it several times before.Nunbers added by Billy T
(1) Gravity is real. centrifugal force is not.
(2) yes - Earth is attracting you and if not supported you fall towards it.
Likewise you are attracting Earth and it falls towards you as you fall. These "equal and opposite" produce very different accelerations in you and Earth, because Earth has much more mass than you, so you do not notice it jumping up to meet you. - Interesting to note that if "you" were a rocket flying along side an asteroid, but thrusting to keep from joining it by mutual gravitational attraction, then the fall of it up towards you (although still small) accumulates and can change its trajectory. This is the best way to avoid it hitting Earth. Blowing it up, as done in a movie, is very bad idea.
(3)No. The centrifugal force is an illusion, not real. If the car seat alone can not supply the force toward the center of curvature, but the friction of tires with road can, then the car will not skid, but follow the curve and you will be slammed in your side by the car door to stop you from follow a more straight line trajectory. I.e. The car door will assist the seat in giving you the required force towards the center of the curve (or your seat belt will) - Your self-centered or biased POV makes you thinks you were thrown against the car door by what you call the "centrifugal force." In reality, all you were trying to do is mind your own business and continue gong straight ahead when the car door said: "No way - you are going to make the curve and I will force you to, if need be." - Or something like that - I did not catch exactly what the car door said. ;)
(4) This makes so little sense to me that I do not know what to say. Surface of Earth exerts forces only on thing touching it, like you shoes when standing.
(5) reactionary force of car door on earth surface??? see (4) again
(6) See 1 & 3 again.
(7) No - only gravity is.
(8) I would hope so* - even Newton did (know there is no such thing as "centrifugal force") If still in doubt, read (3) again (and again, again, etc. till all doubt is gone. - If that does not work, take two aspirins and post again in the morning.) :)
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*If NASA thinks centrifugal force exists, I want my taxes refunded. If an astronaut in an acceleration test centrifuge really thinks his pain and distorted face is caused by centrifugal force then at least He goes back to basics physics class and I want a reduced tax rate (or a job as his physics instructor.) ;)
It is OK by me if he says: "I did not think I could take 6Gs of centrifugal force." - Just as it is OK for him to say: "Launch is 20 minutes after the sun rises." But he dam well better know that there is no centrifugal force and that the sun does not rise - the Earth spins.

A "self-centered" biased POV can be very missleading. If you want to understand anything like quantum mechanics, the first thing you must do is realize that you should trust your equations and instruments, not your pratical experience if it conflicts with them. (usually, at least)

1. "Nothing rests in the world,"

All seemingly solid matter is full of atomic motion.

2. "but magnetism tries to make rest. Absolute rest would be non-existence."

Magnetism attracts things, it makes things unite, so that they would fall into singularity, nothingness. The earth has a magnetic attraction. The source of that power tries to unite with the earth (the repulsive force). It cannot do it because the resistance of matter is more powerful. But imagine that the resistance of matter would weaken, or that the attraction of the earth would become stronger than the repulsive power in matter: the matter would fall into a singularity and nothingness would take their place.

Everything that is visible is visible only because of its "motion" or "vibration".

Rest means balance. Mix black and white colors and they will both stop to exist, and gray will take their place which is both black and white (neither black or white). Gray represents "non-existence" on color level, since it has no opposite color.

Do you mean attractions as in/by magnets/magnetism or gravity tends to unite the things? If yes, how "unite" can be considered as singularity, nothingness?

Entropy: Introduction
Many quantities of matter tend to equalize their thermodynamic parameters - reducing differentials toward zero. Pressure differences, density differences, and temperature differences, all tend toward equalizing. Entropy is a measure of how far along this process of equalization has come. Entropy increases as this equalization process advances. For example, the combined entropy of "a cup of hot water in a cool room" is less than the entropy of "the room and the water after it has cooled (and warmed the room slightly)," because the heat is more evenly distributed. The entropy of the room and the empty cup after the water has evaporated is even higher.

An important law of physics, the second law of thermodynamics, states that the total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value; and so, by implication, the entropy of the universe as a whole (i.e. the system and its surroundings) tends to increase.
http://en.wikipedia.org/wiki/Thermodynamic_entropy

We should understand above concept and of perfect crystal and magnet's concepts while thinking on motion or rest. ??

There is nothing special about magnets, they obey Newton's laws just like everything else.

If you mean what happens on a microscopic level then as a first approximation just consider that all the atoms in a piece of iron are like microscopic bar magnets. Normally they are all randomly oriented with no net magnetization, but in the presence of a strong magnet they align to produce a net magnetization and hence the magnetic force. This alignment really has very little to do with thermal motions and vibrations.

-Dale

What is the difference between a perfect crystal and a perfect magnet? Are these both alignment of their internal structures based?

Nunbers added by Billy T
(1) Gravity is real. centrifugal force is not.
(2) yes - Earth is attracting you and if not supported you fall towards it.
Likewise you are attracting Earth and it falls towards you as you fall. These "equal and opposite" produce very different accelerations in you and Earth, because Earth has much more mass than you, so you do not notice it jumping up to meet you.

Attractions and repulsions are two aspects common in all magnetism. Does gravity always attracts? How can we differenciate between any motion in line of earth's movement and against it? Will opposite forces due to moving opposite to earth's motion not resist/effect motions? How can we treat similar motions in all directions on earth as same?

Whether cooler atmosphere at poles can be due to lesser motion/force at poles?

On earth, Can we call "rest" as an equalization of forces with that of the surroundings and "motion" as deviations of forces from that of the surroundings? :)

Still it can't be considered as "absolute rest" or "absolute zero" on earth which is an non-inertial stiuation". What is the average tempereture on earth?

I agree a 'self-centered, biased' point of view is very missleading. I agree centrifugal force should not classified as a FUNDAMENTAL force as it does not appear in all reference frames, i.e. inertial frames, but I do not agree that there is no such thing as centrifugal force. But, then again, the gravitational force does not appear in inertial frames, does it? The gravitational 'force' also does not appear in General Relativity, does it?

Here is a cut & paste from NASA's site:

"Because the centrifugal force exists only in rotating reference frames, but not in inertial reference frames, it's sometimes called a "fictitious" or "pseudo" force.

We don't like this characterization because there is nothing fictitious or pseudo about it when your car goes off the road and crashes, or when your bicycle skids out from under you when cornering a slippery curve. The Earth's equatorial bulge is not a fiction, nor is the problem an engineer confronts when designing turbine blades of jet engines that have to stay together at rotation rates of up to 100,000 revolutions per minute."
http://observe.arc.nasa.gov/nasa/space/centrifugal/centrifugal5.html

So, Billy T, what causes Earth's equatorial bulge?

If I am inside a windowless room and feel no forces, an inertial frame, how can I tell if I am in gravitational freefall or in deep space? If I am inside the same room and feel 2g's acceleration, how do I determine if the acceleration is due to centrifugal force or if I am on the surface of a planet with twice the gravitational attraction of Earth?

Some of your answers have little thought behind them, Billy T. For example, I asked 'Does the gravitational force have an equal and opposite force' to which you replied "Yes - Earth is attracting you and if not supported you fall towards it." Which force would this be, Billy T? The centripetal force is a center-seeking force like gravity, so what force are you speaking of? If I am in orbit around the Earth, not supported by structure, what force balances the centripetal-like force of gravity?

As to your 'paraphrasing' what I asked in question 4, maybe you should read it again.
I was using the surface of the Earth as analogous to the car door/seat. Both present an obstruction to movement resulting in a felt acceleration, the change from an inertial frame of reference to a non-inertial frame.

(7) You state only gravity is due to a property of mass. Can a massless particle experience the 'false' centrifugal force? No, both forces arise due to a change from an inertial frame to a non-inertial frame for a massive object.

2inquisitive and BillyT, I think we have the following major points of agreement: the centrifugal force exists in the rotating frame, the centrifugal force does not exist in the inertial frame.

I think we also have the following major point of disagreement: 2inquisitive (and NASA) do not like the characterization of the centrifugal force as "ficticious".

I can understand that, because in the rotating frame it is very real and is in fact necessary. In that frame the centrifugal force can indeed cause deformations, stresses, accelerations, etc. In an inertial frame all of those effects mentioned in the NASA quote can be explained just fine without resorting to the use of the centrifugal force. In fact, in the inertial frame trying to include the centrifugal force would lead to incorrect conclusions!

Because the centrifugal force causes very non-ficticious effects in the rotating frame I am perfectly willing to use some other more palatable terminology. How about the term "frame force" instead of "ficticious force". This emphasizes the source of the force without de-emphasizing the very real effects of such a force in the non-inertial frame.

As far as gravity goes, I understand that it is considered a real force in classical mechanics and a frame force in GR. That is due to the difference between the two theories in the definition of which frames are inertial. My limited understanding is that the whole purpose of using curved spacetime is to permit the GR definition of an inertial frame. I chose my example to be a deep-space station precisely to eliminate gravity as a potential source of disagreement and confusion. I understand both views, but unfortunately I do not know the math to work with the GR view, so I generally prefer to consider gravity as a real force and use the classical definition of inertial frames (if that is ok with you two). Since we aren't dealing with black-hole type masses or other situations requiring relativistic corrections then I think there should be no problem with the results.

-Dale

Sorry about the long strings of quotes, I just wanted to put in my 2 cents worth in two of the points here.


The surface of the Earth exerts an equal and opposite reaction to offset the acceleration of gravity. Without the reactionary force of the car door or the Earth surface, neither the car driver nor the person standing on Earth would feel either force. So, why is gravity considered a 'real' force and centrifugal force considered a 'false' force? (2) yes - Earth is attracting you and if not supported you fall towards it.
Likewise you are attracting Earth and it falls towards you as you fall. These "equal and opposite" produce very different accelerations in you and Earth, because Earth has much more mass than you, so you do not notice it jumping up to meet you.I asked 'Does the gravitational force have an equal and opposite force' to which you replied "Yes - Earth is attracting you and if not supported you fall towards it." A "reaction" force is always of the same kind as the "action" force. So a contact force cannot be the reaction force to gravity. If you look carefully at the man-on-the-earth example there are 4 forces, two on each object. The earth exerts e.g. a 150 lb downward total gravitational force on the man which is distributed over every atom of his body. The reaction to this is a corresponding 150 lb upward total gravitational force that the man exerts on the earth which is distributed over every atom of the earth. Since the earth has so many atoms the acceleration due to this 150 lb upward force is negligible, but it is still there. The earth also exerts a 150 lb upward total pressure force distributed over the soles of the man's feet. The reaction to this is a 150 lb downward pressure force on the earth distributed over the ground under the man's feet. Although this force is no larger than the gravitational force it may not be negligible (e.g. if he is standing on mud) due to the more concentrated distribution. Neither the earth nor the man accelerate because both experience a gravitational and a pressure force that are equal and opposite.

In summary reaction forces will always be the same kind of force as the action forces. That applies for gravitational and contact forces as shown here, but also electromagnetic, strong, weak, or any other forces. I don't know how frame forces fit in since the frame force exists for a single object in isolation where there can be no action-reaction pair. Nor do I know how the gravitational force fits in with GR where it is considered a frame force.


So, why is gravity considered a 'real' force and centrifugal force considered a 'false' force? Both are due to a 'property' of mass, correct? (7) No - only gravity is.(7) You state only gravity is due to a property of mass. Can a massless particle experience the 'false' centrifugal force? No, both forces arise due to a change from an inertial frame to a non-inertial frame for a massive object.I think that in a rotating reference frame light would be deflected even if you do not consider it to have even "relativistic mass". I guess it would be more proper to call it a centrifugal acceleration rather than a centrifugal force. I think the same would be true of any frame force or frame acceleration.

-Dale

...So, Billy T, what causes Earth's equatorial bulge?....equatorial earth (dirt, water ) is traveling at approximately 1000mph and thus is slightly more able than polar earth to try to follow Newton's first law (continuer in straight line motion) - same old strory of you in car being forced to travel in a circle and being slammed by the door to do so. Merri-go- round is same story too.

...If I am in orbit around the Earth, not supported by structure, what force balances the centripetal-like force of gravity?...You are missing the main point - Namely that there is no force balance. If there were you would follow Newton's first law and be flying off in a straight line tangent to Earth. An UNBALANCED force due to the attraction between matter, called gravity, is constantly accelerating you towards Earth.

I would prefer "frame effect" to "frame force" as all true forces do have the "equal and oppposite force" of Newton's third law. There are large effects associated with being constrained to a rotating frame (be it the car example or the entire Earth - I.e. the Coriolis "force" is a major contol of the weather, which would be quite different if Earth did not rotate.) I do not want to be in a position that requires one to say:

Newton's third law is valid except for:
(1)centrifugal force, (2)Coriolis force, ...
which are "monoforces" that have no reaction force.

I like the third law just the way it is, no list of exceptions, but recognize that when you take a POV in a moving frame, the physical effects* in this frame can be described as if they were due to a "force" but one should know that it is a “POV force” at best, and as such, different for every different POV.

In some sense, one could also postulate a "bird force" exists even in a non rotating frame. I.e. the reason your gun must be pointing infront of the bird if you are to hit it is to compensate for the "bird force" but I think the conventional view that the bird is in a different inertial frame and that frame, in which it is fixed, will have moved during the travel time of the bullet is a better view. I.e. the "bird force" is really a "frame force" (Dale's term) or as I would prefer, a "frame effect" if we need to give it a name. If you understood the frame effects of rotating frames as well as you understand the "bird force" is a frame effect, you would not be wanting to invent names and non existent forces that violate Newton's third law.
____________________________________________
*I also want to state that the non-existent “centrifugal force” is not the reason why the astronaut’s face is distorted in the spin test centrifuge. His (or her) flabby cheeks did not have any force applied to them in the radial direction when the spin was zero. As the spin began the head rigidly fixed in helmet, which was rigidly fixed to chair, which was rigidly fixed to centrifuge arm, was forced into circular motion, but the “flabby cheeks” briefly had no force still, so they followed Newton’s first law (approximately only as the “zero force” period was of zero duration) I.e. moved slightly more distant from the center of rotation. When they had, on their slightly different trajectory, moved enough relative to the skull, they were subjected to a “collagen stress forces” which quickly made the “flabby cheeks” move in a circle also.

“Centrifugal forces” actually had nothing to do with it. The effects of the “collagen stress forces” are only more conveniently described as if there were “centrifugal forces” acting.

I will not argue this more. I too speak of “centrifugal force” when in general conversation, but when someone asks about Newton’s laws, and for me to explain things, etc, then I must be as honest as I can be. I.e. I must point out that these POV forces are just that - an effect of the point of view, not real forces, not exceptions to Newton’s third law.

OK, Billy T, I will not argue with you, but I see it differently, as do many other physicists. How can you possibly say that an object in orbit is experiencing UNBALANCED forces?? No force is felt in that frame of reference. You are simply insisting on a preferred frame of reference, that of the distant observer.
another quote to support my side of the disagreement:

"Our astronaut aboard the ISS is in free fall, just like the cannon ball. The ISS - and the astronauts - are prevented from being thrown out of orbit (like the water thrown out of the clothes in the spin drier) by the force of gravity. This balancing force is called centripetal force, and keeps the ISS in a closed orbit. Because the centrifugal force is exactly balanced by the centripetal force of gravity the astronauts aboard the ISS will not feel any sensation of centrifugal force. This is another example of the equivalence principle, which says that the effects of gravity and acceleration are indistinguishable from one another, and in this particular case they exactly cancel each other out."
http://www.thekeyboard.org.uk/What%20is%20centrifugal%20force.htm

I will stop with this now, just agree to call it a disagreement.

So, for the purposes of this thread, do we all agree on the following?

1) There is always a frame where an object is at rest (the proper frame).

2) If the proper frame is inertial, then the object can be considered to be at rest.

3) If the proper frame is not inertial, then there will be some type of frame forces/effects and the object cannot be considered to be at rest.

4) The definition of which frames are inertial (and therefore which forces are real) is dramatically different for GR and classical physics.

-Dale

What about the centripetal force due to rotation of earth? What about effects from The Earth's Magnetic Field and polar effects?

Dale, #3 is another point I have questioned in the past. Seated at your computer, can you consider yourself 'at rest'? You feel the force of gravity while seated. Can your frame truly be considered inertial? Special Theory is used in all manner of exercises on the surface of the Earth. In General Relativity, an observer and his frame move through spacetime. In Special Theory of Relativity, an observer considers himself and his frame 'at rest' and all other frames in motion relative to himself as the frame moving. I have stated many times I do not like this POV. Stand outside at daybreak and watch 'the sun rise in the east'. Sit on a pile of clothes in the spin dryer and imagine the dryer housing spin around you. You are not disturbed by centrifugal force and the clothes do not spin dry. But what happens in reality? In the case of the spinning dryer HOUSING, you would still feel the force of gravity pulling on you. In the case of the spinning dryer drum in which you are seated, you would feel the centrifugal force (inertial force) pinning you to the the side of the drum. The forces would feel similar in both cases, but they are considered different frames of reference, one inertial and one non-inertial. But Einstein also says the force of acceleration due to inertia is indistinguishable from the force of gravity. Note: the centrifugal force is an inertial force, but not all inertial forces are centrifugal forces. And just to confuse newcommers to physics more, inertial forces do not appear in inertial frames of reference, they appear in non-inertial frames of reference. Ha!

"Inertial force- (1) The force produced by the reaction of a body to an accelerating force, equal in magnitude and opposite in direction to the accelerating force. An inertial force lasts only as long as the accelerating force does. (2) A force that must be added to the equations of motion when Newton’s laws are used in a rotating or otherwise accelerating frame of reference. It is sometimes described as a fictional force because when the same motion is solved in the frame of the external world, the inertial force does not appear."

Naturally, when there is no motion in inertial frame how there can be inertial force?

Do objects, when at absolute rest in inertial frames or at absolute zero tempreture/energy/motion still have potential energy or not? Whether ansolute rest or zero energy is only related to kinetic energy not to PE?

OK, Billy T, I will not argue with you, but I see it differently, as do many other physicists. How can you possibly say that an object in orbit is experiencing UNBALANCED forces?? No force is felt in that frame of reference. You are simply insisting on a preferred frame of reference, that of the distant observer.


The fact that no force is felt by the the object is not an argument that the object is not acted on by a force or is acted on by balanced forces. It just means that the force is acting on all parts of the object equally.

The rationale for saying that an object in orbit experiences an unbalanced force is the fact that it travels in a circle, circular motion is accelerated motion, and accelerated motion requires an unbalanced force.

Dale, #3 is another point I have questioned in the past. Seated at your computer, can you consider yourself 'at rest'? You feel the force of gravity while seated. Can your frame truly be considered inertial? No, seated at the computer you are definitely in a non-inertial frame. Both GR and classical mechanics agree on this although they disagree on which frame force is the largest. For classical mechanics the biggest frame force will be the centrifugal force from the spin of the earth. For GR the biggest frame force will be gravity. But in both cases the proper frame of a person on earth is a non-inertial frame.

-Dale

Thanks, Janus58. I do understand that point of view. Now, according to an observer on Earth's surface, is the satellite in an inertial or non-inertial frame of reference? According to an observer inside a windowless satellite, is he in an inertial or non-inertial frame of reference?

"Inertial force- (1) The force produced by the reaction of a body to an accelerating force, equal in magnitude and opposite in direction to the accelerating force. An inertial force lasts only as long as the accelerating force does. (2) A force that must be added to the equations of motion when Newton’s laws are used in a rotating or otherwise accelerating frame of reference. It is sometimes described as a fictional force because when the same motion is solved in the frame of the external world, the inertial force does not appear." Definition 2 (aka frame force, fictional force, pseudo force) is the only one we have been using up to this point. Please don't try to introduce definition 1, since there is already enough confusion on this thread.

Naturally, when there is no motion in inertial frame how there can be inertial force?

Do objects, when at absolute rest in inertial frames or at absolute zero tempreture/energy/motion still have potential energy or not? Whether ansolute rest or zero energy is only related to kinetic energy not to PE?Inertial frames do not have frame forces. Frame forces only show up in non-inertial frames. An object at rest in an inertial frame may still have potential energy. It will obviously not have any kinetic energy in it's proper (inertial) frame.

-Dale

Thanks, Janus58. I do understand that point of view. Now, according to an observer on Earth's surface, is the satellite in an inertial or non-inertial frame of reference? According to an observer inside a windowless satellite, is he in an inertial or non-inertial frame of reference?I think, according to GR, that all observers will agree that the satellite's proper frame is an inertial frame. With the curved spacetime of GR there is no problem with two inertial frames accelerating wrt each other nor is there a problem with an inertial frame accelerating wrt a non-inertial frame like that of the earth-based observer.

-Dale

DaleSpam, I agree that classical mechanics and GR both consider the frame to be non-inertial. Special Relativity does not, as I stated in the next sentence. I am, however, confused by your statements about 'frame forces'. In classical mechanics, I thought the biggest force would be the centripetal-like acceleration of gravity, or else the centrifugal force would propel an object into space. In GR, I thought gravity was not a force, that the surface of the Earth exerted a reactionary force to prevent you from following the curvature of spacetime caused by the mass of the Earth, or something like that.

Would following links be useful to you?:m:

Earth's Revolution and Gravity

The first thing to realize is that "centrifugal force" is not real. A
rotating object does not really experience a force away from the center of
rotation. It is just the fact that EVERY object "prefers" to move in a
straight line. When an object is pulled into a circle, there is no force
pulling it out. That is just the object trying to continue in a straight
line. The Earth does not have "centrifugal force".

The Earth does experience a centripetal force: the Sun pulling the Earth
inward. This centripetal force is gravity.
http://www.newton.dep.anl.gov/askasci/phy00/phy00336.htm

Gravitaional and Centripetal Forces

You must first realize that centripetal force is NOT a force. Centripetal
force is an effect of forces directed toward a central point. IF all true
forces add up to a large enough net force, directed at the center of a
circular path, then these forces are able to KEEP the object on that
circular path. The formula for centripetal force is a calculation of how
much force is needed.

When you rotate with the Earth, some of the gravitational force is needed
just to keep you on the Earth's surface.
http://www.newton.dep.anl.gov/askasci/phy00/phy00336.htm

:)**Season's Greeting and Merry X-Mas to all**:)

Definition 2 (aka frame force, fictional force, pseudo force) is the only one we have been using up to this point. Please don't try to introduce definition 1, since there is already enough confusion on this thread.

Ok.

Inertial frames do not have frame forces. Frame forces only show up in non-inertial frames. An object at rest in an inertial frame may still have potential energy. It will obviously not have any kinetic energy in it's proper (inertial) frame.

Thanks. I think it is ok that, potencial energy do not create any temperature in an object?

A perfect crystal is considered as with "absolute zero" motion/energy/temp.. Do deformation of a crystal/concentrated substance into smaller particles/molecules increases total motion/energy/temp. which was there in their crystal form? Whether overall motion/temp. is increased and preserved when a crystal/concentrated substance is converted to powder or diluted on eargt(non-inertal frame) and vice versa?

Can this be be possible:-

First Law of Rest
I. Every object in a state of uniform rest tends to remain in that state of rest unless an external force is applied to it.

The law of inertia of rest may states that:
A body will preserve its position of rest so long as no force for its motion acts on it.

First Law of Motion/Rest may state:
I. Every object in a state of uniform motion/rest tends to remain in that state of motion/rest unless an external force is applied to it.

The law of inertia of motion/rest may states that:
A body will preserve its position [motion/rest] so long as no force for its change acts on it.

Both may be valid in inertial and non-inertial frames considering "surrounding forces" as standard....apparant rest.

Just a thought only. Pls comment. :)

OK, Billy T, I will not argue with you, but I see it differently, as do many other physicists. How can you possibly say that an object in orbit is experiencing UNBALANCED forces?? No force is felt in that frame of reference. ...Not arguing, only answering your question:
You "feel forces" (when they are above a threshold) and act differentially upon your body. For example, the sun is making a greater force on you (and the sea, tides etc) than the moon, but because the moon is much closer and because the force GRADIENT falls off as the cube of the distance, not as the square, the GRADIENT of the moon is greater.

The differential force due to the moon's gravity gradient across small things like a swimming pool or your body is too small to be noticed, by humans, at least, but some smaller, more sensitive, creatures like claims can. (Tides are very important to clams - to know when it is safe to open and not dehydrate etc.) Clams kept in dark and transported to Chicago by airplane, keep the old rhythm for a few days then go onto the schedule of "Chicago tides" if there were such things.)

You can make any uniform force vanish by transferring to a suitable frame of reference, but not its gradient. The astronaut had significant gradient across his face in the test centrifuge, but not when in orbit. In neither case did a "centrifugal force" exist. The difference in what he feels, "experiences" is due to the difference in the force gradients.

You feel acceleration in you car because parts of your body can only match the cars acceleration by moving so that other part of the body supply the accelerating forces that keep them attached to you. If you were inside a water tank on a truck with the same acceleration, more of the required acceleration could act on these parts directly and you would feel the acceleration less.

I have been scolded already today in another thread for being so "long winded" so I stop here and hope you understand the you need not feel an unbalanced force that is accelerating you with very little local gradient.

By edit: I now have read Janus58 and see he said same thing better in many less words, but at least you may have learned something about clams. I some times worry about eating creatures that are 1000 times more sensitive than me.

In classical mechanics, I thought the biggest force would be the centripetal-like acceleration of gravity, or else the centrifugal force would propel an object into space.You are getting confused by the difference between frame forces and real forces. In classical mechanics gravity is a real force. In earth's proper frame the biggest classical frame force is the centrifugal force, but you don't fly off into space because the real force of gravity is much greater than the centrifugal frame force.

In GR, I thought gravity was not a force, that the surface of the Earth exerted a reactionary force to prevent you from following the curvature of spacetime caused by the mass of the Earth, or something like that.In GR gravity is not a real force, it is a frame force. Just like the centrifugal force, it only exists in a non-inertial frame. According to GR the proper frame of a person standing still on the surface of the earth is accelerating upwards at g. In this accelerated frame we need to include a downwards frame force of m g in order to explain motion and other effects. According to GR the gravitational force in this accelerated frame is no more (nor less) real than the centrifugal force.

-Dale

Thanks. I think it is ok that, potencial energy do not create any temperature in an object?There are a variety of different forms of potential energy. Many have no effect on temperature, such as gravitational potential energy and electrical potential energy. Chemical potential energy can actually reduce temperature, like a reversible endothermic reaction. I don't know how elastic potential energy and temperature may be related. In an ideal gas PV can be considered potential energy and it is proportional to temperature. But there is no general relationship between most forms of potential energy and temperature.

A perfect crystal is considered as with "absolute zero" motion/energy/temp.. Do deformation of a crystal/concentrated substance into smaller particles/molecules increases total motion/energy/temp. which was there in their crystal form? Whether overall motion/temp. is increased and preserved when a crystal/concentrated substance is converted to powder or diluted on eargt(non-inertal frame) and vice versa?I have no idea what a perfect crystal would be. I have never heard of perfect crystals except in your posts on this thread, so I really cannot say anything reasonable about them.

-Dale

Can this be be possible:-

First Law of Motion/Rest may state:
I. Every object in a state of uniform motion/rest tends to remain in that state of motion/rest unless an external force is applied to it.

The law of inertia of motion/rest may states that:
A body will preserve its position [motion/rest] so long as no force for its change acts on it.
Yes, you are basically just restating Newton's first law.

-Dale

Yes, you are basically just restating Newton's first law.

-Dale

But why then, word "rest" was not used/considered?

Can you tell me this:-

On earth(non-inertial frame), suppose a crystal made up by one million molecules with their individual energy E1, and surrounding forces F, have a total Energy E. It is triturated to fine powder by applying external energy E2. Say, total energy in all one million molecules in powder form is E3. Will then:-

Before trituration:

E= F + (E1 x One million)

After trituration:

E3 = F + E2 (E1 x One million) or

if E2 is essentially to be lost as heat

E3= F + (E1 x One million) = E

Ok?? However, I feel E1 (energy of individual molecule) changes and preserved in molecules on converting crystal into powder form in non-inertial stiuation(earth) but may not change in inertial stiuation. ?? I also feel this additional energy added due to extra F applied to molcules(more free) in powdered form than in crystal form(more bonded) and/or from the applied energy required to powder the crystal. Energy lost as heat may be from breaking the molecular bonds on triturating+ Some out of applied energy.

I am also considering thermal/thermodynamic equilibrium here because I feel, energy of molecules E1 is different/lesser when they were in crystal form than when they are in powdered form. Whether this change in energy is potential or kinetic(more vibrations) is to be seen?

by Kumar:

"But why then, word "rest" was not used/considered?"
================================================== ==============

Newton DID use the state of rest in formulating his first law. His statements, written in Latin, are sometimes changed and shortened by others. You just need to read more references and explainations. He also used centrifugal force in his original papers, before being convinced by his rival, Robert Hooke, that the use of one force could also explain his rotating frames. Here is a link to Newton's work:

"Axioms, or Laws of Motion
14 Law I. Every body-perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon. Projectiles persevere in their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force of gravity A top, whose parts by their cohesion are perpetually drawn aside from rectilinear motions, does not cease its rotation, otherwise than as it is retarded by the air. The greater bodies of the planets and comets, meeting with less resistance in more free spaces, preserve the motions both progressive and circular for a much longer time."
http://en.wikisource.org/wiki/Philosophiae_Naturalis_Principia_Mathematica#Axiom s.2C_or_Laws_of_Motion

Also, concerning centrifugal force, many scientists other than NASA use its equations, principally atmospheric scientists.

Here is an excerpt and link to another NASA site, illustrating several examples of why centrifugal force is used by them in many of their calculations:

"Assuming the Earth is exactly spherical, we expect gravity to always point towards the center of Earth. However, the centrifugal force is perpendicular to the axis of the Earth. Except on the equator, therefore, it is not exactly opposed to gravity, but adds a small horizontal vector component, pointing towards the equator (dashed arrow in the figure). As a result, not only is effective gravity weakened, but its direction is modified--instead of pointing to the center of the Earth, it slants (ever so slightly) towards the equator.

Does this mean that if you placed a perfect ball on a very smooth horizontal surface, gravity would make it roll equatorward...? Suppose it was so. That same force would also act on the water of the ocean and make it flow equatorwards, and even the solid Earth might deform!

How long would this go on? Well, until the equatorial pile-up of material forms a "hill" around the Earth, rising slightly towards the equator, where its top would be. No more flow towards the equator would occur once the slope of the ground, as modified by the hill, would be exactly perpendicular to the effective direction of (modified) gravity. With such a slope, a perfect ball placed on a perfectly horizontal surface would no longer try to roll anywhere, and forces on oceans and on land would no longer try to move matter horizontally.

By now you should realize what this gives us--an explanation to the equatorial bulge of the Earth! That bulge is nothing but the "hill" described above, and the shape of the surface is such that the ground is always perpendicular to the effective gravity"
http://www-spof.gsfc.nasa.gov/stargaze/Srotfram1.htm

"Axioms, or Laws of Motion
14 Law I. Every body-perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon."

2inquisitive, how a body can preserve state of uniform motion when in inertial stiuation or in absolute zero state of energy?

I'm not sure I understand your question, but the body is not in an absolute zero state of energy. Perhaps you were confused by the statements about kinetic energy. Some use the statement that a body has no kinetic energy in its rest frame, I suppose to infer the object has no additional kinetic energy in its own inertial frame due to motion. But, viewed from an outside frame of reference, a body in motion in an inertial frame has more kinetic energy than an identical body at rest relative to the outside frame of reference. The problem is WHICH frame is 'really' at rest, so it is always postulated to be the observer/body that is at rest in his/its own inertial frame of reference when ONLY two frames of reference are used. When an observer is in a third frame of reference, two bodies can both be in motion, only one of them, or neither can be in motion relative to this observer. An example would be a physicist at a particle accelerator facility recording the kinetic energies of colliding particles.

I'm not sure I understand your question, but the body is not in an absolute zero state of energy. Perhaps you were confused by the statements about kinetic energy. Some use the statement that a body has no kinetic energy in its rest frame, I suppose to infer the object has no additional kinetic energy in its own inertial frame due to motion. But, viewed from an outside frame of reference, a body in motion in an inertial frame has more kinetic energy than an identical body at rest relative to the outside frame of reference. The problem is WHICH frame is 'really' at rest, so it is always postulated to be the observer/body that is at rest in his/its own inertial frame of reference when ONLY two frames of reference are used. When an observer is in a third frame of reference, two bodies can both be in motion, only one of them, or neither can be in motion relative to this observer. An example would be a physicist at a particle accelerator facility recording the kinetic energies of colliding particles.

Let us try to understand it by real frames...Space and Earth, where say, in space there is no external forces, whereas many external forces are there on earth. There is an average of all forces on any place of earth. Now when a body moves in space or is at rest, it can continue uniformally as there is no average surrounding force but when that body moves or at rest on earth, it should be always in motion really due to external forces deviated as from absolute zero. But still it will be in accelrated motion(if running) or in apparant rest(if resting). So real/absolute rest frame for that body will be the space and apparent rest frame will be the earth. Body running by additional forces on earth will be in apparent motion equal to velocity and direction but still it will be in addition to motion caused by average forces on earth at that place. For rest and motion at earth we are just discounting/ignoring average applicable forces on earth at that place--for apperant/practical purposes. Now Pls tell what you mean>




On earth, "Molecules/particles in crystal or in some other concentrated form can have less "kinetic" but more "potential" energy whereas molecules/particles in its triturated/diluted or seprated form can have more "kinetic" but less "potential energy"...somewhat alike in magnets."

Is it ok?

Here is an excerpt and link to another NASA site, illustrating several examples of why centrifugal force is used by them in many of their calculations:

"Assuming the Earth is exactly spherical, we expect gravity to always point towards the center of Earth. However, the centrifugal force ... and the shape of the surface is such that the ground is always perpendicular to the effective gravity"
http://www-spof.gsfc.nasa.gov/stargaze/Srotfram1.htmVery nice quote. The bulge can be explained in an intertial frame also, but the explanation in the rotating frame is much simpler. I think this is a good demonstration of why non-inertial frames are often used.

-Dale

On earth(non-inertial frame), suppose a crystal made up by one million molecules with their individual energy E1, and surrounding forces F, have a total Energy E. It is triturated to fine powder by applying external energy E2. ...

Ok?? However, I feel E1 (energy of individual molecule) changes and preserved in molecules on converting crystal into powder form in non-inertial stiuation(earth) but may not change in inertial stiuation. ?? I also feel this additional energy added due to extra F applied to molcules(more free) in powdered form than in crystal form(more bonded) and/or from the applied energy required to powder the crystal. Energy lost as heat may be from breaking the molecular bonds on triturating+ Some out of applied energy.I do not know if a crystal has more or less chemical energy in its original or pulverized form, but I cannot imagine what effect the frame would have on the chemical energy. As far as I know the frame will only alter your KE and your gravitational PE.

I am also considering thermal/thermodynamic equilibrium here because I feel, energy of molecules E1 is different/lesser when they were in crystal form than when they are in powdered form. Whether this change in energy is potential or kinetic(more vibrations) is to be seen?Thermodynamic equilibrium is achieved when the whole system is at a uniform temperature, not when the whole system has no molecular vibrations. In other words, if you want to consider a thermal state of "absolute rest" to have no molecular vibrations then you are talking about absolute zero which will have to continuously move energy away up the temperature gradient. If you want to consider a thermal state of "absolute rest" to have no energy transfer then you are simply talking about a uniform temperature.

-Dale

I do not know if a crystal has more or less chemical energy in its original or pulverized form,...I do not have time to read the may posts that have appeared here since my last, but will say a few words about this. The creation od suface area always requires energy, and as this is related to the bonding between atoms, I think it should be called "chemical energy."

Imagine a large cystal, being slowing pulled apart. I.e. work is done to make it into two smaller ones whose total surface area is greater than the original. The is new surface is where that work/energy resides now. Continue making ever smaller ones, until you have crystal "pulverized."

If it happened to be a crystal that can be oxidized (iron or copper etc.) then then 1 gram of pulverized will yield more heat than one gram of solid crystal as in the solid case, part of the heat of oxidation is needed to separate the atoms of the crystal. - more reason to call the extra energy in the pulverized crystal "chemical energy."

The creation od suface area always requires energy, and as this is related to the bonding between atoms, I think it should be called "chemical energy."Works for me. Of course, you would have to consider it potential energy.

Although to be honest I don't understand why Kumar is bringing it up. It seems irrelevant to the thread since I would imagine that a bunch of powder could be at rest just as easily as a solid crystal. I don't think that potential energy of any kind has any bearing on an object's state of rest.

-Dale

Let us try to understand it by real frames...Space and Earth, where say, in space there is no external forces, whereas many external forces are there on earth. There is an average of all forces on any place of earth. Now when a body moves in space or is at rest, it can continue uniformally as there is no average surrounding force but when that body moves or at rest on earth, it should be always in motion really due to external forces deviated as from absolute zero. But still it will be in accelrated motion(if running) or in apparant rest(if resting). So real/absolute rest frame for that body will be the space and apparent rest frame will be the earth. Body running by additional forces on earth will be in apparent motion equal to velocity and direction but still it will be in addition to motion caused by average forces on earth at that place. For rest and motion at earth we are just discounting/ignoring average applicable forces on earth at that place--for apperant/practical purposes. I think you are understanding now. As you have seen we use the terms inertial and non-inertial. In your example the "space frame" would be an inertial frame, while the "earth frame" would be non-inertial. A person resting would be at rest in the earth frame, but would not truly be at rest because the earth frame itself is accelerating. A person running would be moving in the earth frame which in turn is accelerating. An object at rest in the (inertial) space frame would be truly at rest, not accelerating in any way.

-Dale

Billy T, thanks but. will molecular bonding in crystal be more relavant thought instead of atomic/chemical bonding? Does surface/closed atmosphere as in crystal. restrict motion/temp. of molecules in crystal and so the thermo-dynamic equib. with surrounding atmosphere?

I think you are understanding now. As you have seen we use the terms inertial and non-inertial. In your example the "space frame" would be an inertial frame, while the "earth frame" would be non-inertial. A person resting would be at rest in the earth frame, but would not truly be at rest because the earth frame itself is accelerating. A person running would be moving in the earth frame which in turn is accelerating. An object at rest in the (inertial) space frame would be truly at rest, not accelerating in any way.

-Dale
Yes, thanks for