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Author Topic: Why does a train platform appear to move?  (Read 1462 times)

Offline pushkar

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Why does a train platform appear to move?
« on: 26/03/2010 11:32:39 »
when the train is moving the railway platform appears to be moving in opposite direction which is due to the motion of the image of the platform on the retina in the opposite direction to that  of the train.Is it true that motion of train is real because force has been applied to the train while motion of platform is apparent and hence two frames are not equivalent?


MOD EDIT - Pushkar - Please format your subject as a question - you have been asked many times.
« Last Edit: 26/03/2010 12:40:17 by BenV »


 

Offline pushkar

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Why does a train platform appear to move?
« Reply #1 on: 27/03/2010 08:33:15 »
i shall do in future as as advised
thanks
 

Offline graham.d

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Why does a train platform appear to move?
« Reply #2 on: 27/03/2010 10:24:09 »
It depends on how you want to view this. Clearly in everyday life the two frames are different in that being on a moving train will have a different overall effect on you from standing on a station platform. However, I imagine that you are thinking of the moving train idea that is used in physics thought experiments. Here the train is rather idealised but the principles are right. In this case, if the train is at a constant speed and moving in a straight line, any physics experiments you do on the train would give exactly the same results as those on a station platform. The two frames are both "inertial" frames and neither is special in any way.

If you were in space and threw a criket ball, you would move one way and the ball the other. The force acted on both you and the ball, and both motions are real. It is not obvious because the effects are so small, but the acceleration of the train would have caused the earth to move slightly too because of the traction of the driving wheels on the rails. In this sense you can say neither motion is unreal. You can only say that the train is moving relative to the platform. You can indeed calculate from accurately measured accelerations that you are on the lighter body (compared with the earth) and have been accelerated more that the earth has.

Anyway, in everyday life, you can generally take the earth to be a reference frame and assume that it is you that is moving :-)
 

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Why does a train platform appear to move?
« Reply #2 on: 27/03/2010 10:24:09 »

 

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