Inertial Frames are Not Equivalent

:shrug:
Case 1:
Drop a golf ball from a train moving with constant velocity onto a grainy surface that lies parallels to the train tracks.

If the train is actually in motion relative to the embankment the ball will bounce back up the original trajectory wrt the train with some losses due to friction in the bounce point. The reflected ball then exhibits the conservation of momentum [of the moving train].

If the it is the embankment that is moving and the train stationary, then when the ball strikes the grainy surface the ball will be deflected in the direction of the moving grainy surface due to the exchange of momentum of the stationary ball with the moving grainy embankment a mchip shot of sorts.

The latter case is never observed.

Likewise, one can always determine the acceleration of trains pulling out of stationary stations and one can never measure the acceleration of an embankment wrt a train using accelerometers placed on the embankment.


Case 2:
Take two inertial platform moving relative to each other parallel along the long axis of both frames. Frame A ejects golf balls perpendicular to the relative motion of Frame A and B and the balls strike the flat grainy side of frame B and are reflected some angle wrt the motion of the ejected balls. Now, if FA is at rest relative to some known point (some x,t, where mthe x,t is not known by observers on Fa and FB) on the surface of the earth, for instance, then FB will "own" all the relative motion of the FA/B system or, FB - FA = Fba where Fba is the relative velocity of the FA and FB system, here FA = 0.

The balls reflecting off the grainy surface of FB will be deflected in the direction of FB motion, the angles of which which can be calibrated in the lab.

If FB is at rest and FA owns all the relative velocity of FA/B system then the ball ejected from FA will be reflected off the FB surface in the direction of the moving FA. Again all reflected angles can be calibrated in the lab, hence allowing determination of the absolute velocity of FA wrt FB.

All of this of course follows from the principle of the conservation of momentum, doesn't it? Even when both FA and FB are in motion wrt some knowable rest point in space.
:shrug:
​

 

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Inertial frames don't experience acceleration. Otherwise they wouldn't be inertial.

And in the case of the ball, it'll receive the same 'kick' from bouncing off the station/embankment in both cases.

Besides, using a vague physical system and avoiding doing any precise experiments to take into account all factors and doing the maths, you prove nothing.

It's like people who think that magnets expend energy to stick to fridges because if we push on a wall, we get tired even though we don't move anywhere. Our muscles don't work like magnets, but some people still ignore this.

 

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Hello geistkiesel, et al.

Looking at case1 with energy conservation in mind then then the ball will have both spin and a deflection/bounce angle. The balls total energy/momentum will remain constant and will consist of a change of speed (wrt the balls origin frame) and spin.

If the ball reflects off a grainy surface of the original frame (a steady state reflection/bounce) then the "spin" component is a function of the relative velocities. IE A ball with the correct "spin" will bounce back to the original frame with out any deviation as long as the relative velocity, between the frames, remains constant.

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Reminder: this thread is aimed at the inequality of inertial frames.

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So where does this statement fit in the mode of this thread? The entire discussion re conservation of momentum (see any first year college physics text) is confined to inertial frames. The discussion re "acceleration" went to determining which of two inertial frames had originally started their motion with some acceleration, acceleration being a necessesary process in the creation of relative motion of one frame at rest wrt to another frame.

Did you read and comprehend the part about "conservation of momentum"? The ball dropped from the moving train will maintain most (some friction losses are expected) of its momentum in the train direction. When the ball is dropped from a train at rest, wrt the embankment, the "moving embankment" will empart a momentumj impulse in the direction of the moving embankment. However, AlphaN, there is no "both cases" as the embankment will never move wrt to a stationary train. One could simulate the moving embankment with some treadmill apparatus, however. Didn't your graduater advisor tell you that, even? If not then I would for sure [sue to] get my money back 'cause you been thoroughly screwed by one that apparently doesn't know from which he spake.

Fine, then we can expect you to absent yourself from further participation in this thread, can we not? Unless, of course, you would like to perform some 'precise experiments', 'doing the maths' and disproving what is obvious from a simple examination of reality. Can you do it, sir? The "vague train" system was used extensively by AE et al which you can easily discover from AE's book "Relativity".

You seem to have serious personal problem with this thread, discouraged, angry (at being taken in by relativity therorists?), forgetting to critically analyze what some idiots poured into your memory banks, fuming at having been taken in, a smart guy like you, no way!!?

Thinking is more than rote repetition of that those quasi scholars fed to you regularly in the slot under your door, but I speculate here, so don't quote me until the peer review process, re rot repetition, is completed, promise now?

I will leave fridge magnets and the theory of wall pushing (TOWP) to your obvious higher expert attention. Wow, who woulda thought that about fridge magnets anyway? But I did have a fridge magnet fall off thye fridge once, what about this example? Does it upset your fridge thewory of magnetism?

What you have just said is truly amazing, I suppose. We'll all be waiting with bated breath for your Nobel Lecture on the universal kitchen shattering propositions attached (no pun intended here) to Fridge Magnetism. BTW, does FM exclude washer and dryer magnetism?

Please brief us: Exactly what does fridge magnetism and TOWP have to do with the simple demonstration of the inequality of inertial frames? Exactly.

Don't bother us.
:shrug:​

 

spin and linear velocity as parameters in inertial frame inequality experiments.

Hello,, Montec, et al.

True enough, Sir Montec. The ball picks up spin and velocity is changed.

I am not sure I understand completely to what frame you refer re, "the original frame." I considered the train and the embankment as separate frames of reference. I think I agree however. One might add that the "spin" component is also a function of the ball/grainy-surface frictional interface.

As long as we are exploring as we are then discussing 'inertial frames' there is no allowed change of relative velocity - forgive this pedantic triviality.

I suggest that your contribution here has opened up other parameters to investigate in determining the measure of absolute velocities wrt to inertial frames of reference. Angle of reflection is a gross first order measurement. Rotational and linear velocity changes imposed on the ball are added parameters lending to an increase in experimental resolution and minimization of experimental error.
Thank you, Sir montec.:shrug:
​

 

Firstly, momentum is not conserved in the ball in this case, because it's reversing vertical directions. The ball collides with the Earth and some momentum is exchanged between ball and Earth. However, aside from effects due to friction, the horizontal component of momentum is a conserved quantity. Secondly, either P.O.V. yields the same results in your example. From the P.O.V. of the train, the ground is in motion and will drag the ball slightly towards the back of the train when it bounces. From the ground's P.O.V., the ball will be moving forward with the train as it falls, then friction with the ground will cause it to slow down a bit so it drifts towards the back of the train. Same result follows from either inertial frame.​

 

You pick an inertial frame within which to do your calculations. If you don't and your frame (say the train accelerating or the twin in a rocket in the twin 'paradox') then you find something is wrong when you do calculations and your concepts don't square with your calculations.

Basically, you've been sloppy.

CPTBork has explained it better than myself.

Firstly, when I typed my reply, I was perfectly calm, though a little short on time. Secondly, you are making a claim which goes against not just Einstein but Newton, so about 350 years of physics. Rule number 1 when going against mainstream physics : Prove you understand the physics perfectly and have covered every possible way of analysing the situation. You didn't. You provided zero calculations, just a half hearted explaination of a section of physics you haven't thought enough about.

I have done the calculations for such things before. And to be honest, they are boring. But maybe you know that and that is why you haven't done them?

It would seem you have a chip on your shoulder about people who can do relativity and the people who teach it. Your description of my (supposed) method of learning and the people who taught me shows a lot of vitriol.

My point is that it's easy to end up making huge claims because of a little bit of miscomprehension. People have written entire books (see 'The Final Theory') on their new physics model because they didn't bother to learn the simplest bit of physics. You're now claiming that the classic 'train and station' example known to everyone is wrong. So for 100 years of relativity and 250 years previous for Newton (since nothing in your post actually involves relativity) everyone in physics has missed something immediately infront of their face which is obvious from no calculations?

Or, in a moment of humility, perhaps you could consider it's you and you go to learn a bit more? You're having a go at me for being so high and mighty but I'm not the one claiming all that....

 

geistkiesel, you set up a weak straw man in this post and then tore it apart. In fact, you didn't do much of anything in this post because there is no mathematics in the post.

I agree, accept for a minor discrepancy.

Firstly, I agree with AN wholeheartedly. Physicists at the start of the 20[sup]th[/sup] century had no problem with Einstein's first postulate because they already accepted it as true. All inertial reference frames are equivalent in Newtonian mechanics because \(F=ma\), not some combination of position, velocity, and acceleration.

Now for my minor gripe. Newton published his Principia 321 years ago. However, the equivalence of all inertial reference frames go back even further in time than Newton. Einstein's special theory of relativity is not the first theory of relativity in physics. The roots of Einstein's first postulate lie in this first theory of relativity, Galilean Invariance, which was published by Galileo 376 years ago. All in all, a very minor gripe.

 

I was averaging between Galileo and Newton

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minor thing: Einstein's postulate is about all of physics while the one that they had accepted at the start of the 20[sup]th[/sup] is about mechanical laws, isn't it?

 

That's correct. Physicists at the end of the 19[sup]th[/sup] century were confronted with a very serious inconsistency between Maxwell's equations and Galilean invariance, or Galilean relativity. Einstein replaced Galilean relativity with special relativity but maintained the underlying concept of the equivalence of all inertial reference frames.

 

If a ball, stationary wrt the embankment, is dropped onto a grainy surfaced treadmill the ball will be propelled in the direction of the treadmill surface, not unlike a chipshot. The ball will acquire a component of momentum in the direction of the treadmill surface that cannot be ascribed to friction.

If the ball is dropped from a moving train onto then surface of the now stationmary treadmill the ball will retain its forward momentum with slight friction losses and will, hence, bounce up along the same trajectory (wrt the train platform) corrected by the friction losses.

An observer on the train will see the bounce follow the original trajectory will friction corrections imposed. An observer on the ground will also see the ball maintaining the same trajectory wrt to the train (say a vertical strip painted on the outside of the train). For an XY physical axis attached to the embankment both observers will see the same trajectory wrt their own and the others':shrug: frame of reference.

When the embankment that is moving (we need a real treadmill) there is no momentum component other than vertical, therefore when the ball strikes the treadmill surface the trtain observer will see the ball bouncing backward with an angle consistent woth the momentum induced by the treadmill, as will thye observer on the treadmill and the embankment.

Your response did not discuss the treadmilll motion case.

 

The train only accelerated from the station as I explained when describi8ng the impossibility of the station accelerating. During the dropped ball experiment the train was an inertial frame. You didn't read the thread you idiot.

Go fuck yourself.

 

Interesting opinion, but void in physics.:shrug:

 

No, friction is the force responsible for giving your bouncing ball momentum. If it negligable when the train was moving, then it is negligable when the ball is on the treadmill, and in both cases the ball bounces stationary relative to the observer who dropped it.
If it is non-negligable, than it bounces slightly in the direction of travel of the ground relative to the person who dropps it. Towards he rear of the train, or the direction of the treadmill.
They are equivilent in either case, you simply mixed two different scenario's.

-Andrew

 

A slight correction here might be of assistance to you both: Some should be substituted in as a qualifier for "physicists".

Whatever the rest of humanity, including all those dead people you both mentioned, the gedenken experiments described in the thread, which include the train and embankment scenario plus the two inertial objects in field free space were not addressed.

Are you both historians or do you claim some personal talents in dealing with thought experiments as they are handed to you? If the latter, what do you offer to this thread instead of your naive historical trivialities.

To this date all physicists do not agree with the special theory of relativity. I thought you kinew that.:shrug:

 

Andrew,

I will increase the granularity of all surfaces and minimize friction losses. We will concentrate on the case of two inertial frames in gravity free space, calling one platform FA, the other FB. The x axis is along the shortest distance between FA and FB. The y axis is in the direction along the elongated FB. FA and FB are initially at rest wrt each other. We accelerate FB to some convenient inertial velocity v3 wrt the origin, or the position of the nonmoving FA.

Case 1.
Now we eject the ball with velocity v1 from FA perpendicular to the [granular] side of the moving FB. The total initial momentum of the ball with mass m is then mv1. After striking the side of FB the total momentum is m(v2 + v3) where v2 is perpendicular to the direction of motion of FB (along the x axis) and v3 the parallel velocity wrt the motion of FB (along the y axis). The absolute velocities on the x axis are the same in the original and reflected directions. There will be the added momentum of mv3 in the direction of the moving FB.

Observers on FA will see the ball has acquired a velocity component in the direction of the motion of FB, after reflection. The ball will appear to be moving the same velocity as FB to all observers. Observers on FB will see the ball initially coming to a point on FB and then after reflection they will see the ball with a velocity component parallel with FB at a velocity v3.

Case 2
Now we stop the FB motion wrt FA, and now accelerate FA to an inertial velocity v3 and eject a ball to the granular side of FB with velocity v1. The initial momentum wrt the origin is mv1 + mv3 and as v1 only changes direction (180 degrees as in Case 1) after reflection the final additional momentum zero, hence zero change in absolute momentum is observed.

In case 1 observers on FA looking straight along the trajectory of the ball will observe the ball to not reflect back up the original trajectory. Instead, as they widen their view they will see the ball has acquired a velocity component along the y axis. In Case 2, however, the ball will reflect back up the original trajectory as observed by the FA observer looking down the original trajectory.

Also in case 1, the observers on FB will see the ball approaching a predictable point on the side of FB and after reflection the FB observers will see the ball with an acquired velocity component parallel and equal to the velocity of FB.

In Case 2 the observers on FB will see the ball approaching a predictable point on the side of FB and they will see the ball with an unchanged velocity component after reflection.

In both cases we can neglect the velocities perpendicular to the relative frame motion before and after reflection. We only enquire then if there are any measured velocity components added, or lost, after reflection.

Now we have set the origin as stated and such an origin is not know to the observers on FA and FB. All the observers have to rely on is their observations. We may, of course, exclude the measured accelerations to both frames in both cases as such information can be easily communicated to the other frame observers plus such measurements will give cause for the observers to question whether they have, in fact been accelerated and therefore is the frame that is actually moving.:shrug:​

 

The frames used in the original post of this thread were inertial frames. Your reading is, was, rather sloppy, don't you agree?

Since you brought up the twin paradox which was resolved by many in a very strange way. Feynman, for instance, stated that as it was the twin on the space ship that actually accelerated, this was the frame that was actually in motion. Therefore says Richard ., the space ship twin will not age as rapidly as her earth located twin.

Now, when we apply the equivalence of inertil frames to the twin story we see that only the moving frame will generate relativity effects. So much for the equivlence of inertial frames of reference. Sure, yopu might want to say that when the twin returns all will see that only one twin was younger, but during the motion neither twin could tell that it was the other twin that was actually moving.

This last statement needs a qualification. Placing accelerometers on the space ship and the earth only the space ship will have an observed acceleration all of which is known from the get go. Hence, we have to peel these observations from the minds of observers on the earth and the ship in order to maintain some semblance of the equilance of inertial frame postulates.

I have no chip on my shoulder, I just react accordingly to those who post snobbish and insensitive posts as you you posted in your original reply to this thread. Very little of your post, if any, was critical of the arguments given in the original post. You seem to have a revulsion of gedenken ex-periments. You err in the claim that I 'have a chip on my shoulder'. I have found in my short sweet life that any manner of speech directed at stupid people is equivalent. Do you get my drift here AN, ol' chap?:shrug:

 

Granularity creates friction. And what is 'frictional losses'? Are we worried about heating the ball, or slowing it down, or what? Because the only forces that the platform can exert upon the ball bouncing on it are 1: the normal force, which always acta perpendicular to the contact surface (this is what makes the ball bounce up, but it will have no bearing on its horizontal momentum if the surface is perpendicular to the ball's fall direction) and 2: the force of friction, which will act parallel to the contact surfaces, and hence, allow for the ball to gain/loose some horizontal momentum, provided they are moving allong the parrallel axis relative to each other.

No, that is not what will happen at all. You just did what I said you did all over again:
In case two, the force of friction will cause the ball to loose some of it's momentum in the direction of travel (as opposed to the direction of 'fall'), relative to your FB platform. It's that same force of friction that caused it to gain horizontal momentum in the case one.
Again, you have accounted for it (friction) in case one, and dismissed it in case two. Of course they don't add up, they aren't even the same scenario.

Why don't you try making a force block-diagram of the situation?

-Andrew