Laws of Motion/Rest?

[c7ityi_]

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]

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.)
_____________________________________
*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)

 

[Kumar]

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. ??

 

[Kumar]

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?

 

[Kumar]

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?

 

[Kumar]

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?

 

[2inquisitive]

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.

 

[DaleSpam]

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

 

[DaleSpam]

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

 

[Billy T]

...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.

 

[Billy T]

...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.

 

[Billy T]

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.

 

[2inquisitive]

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 is centrifugal force.htm

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

 

[DaleSpam]

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

 

[Kumar]

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

 

[2inquisitive]

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!

 

[Kumar]

"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?

 

[Janus58]

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.

 

[DaleSpam]

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

 

[2inquisitive]

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?