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# Special Relativity -Time Dilation watch

1. In the photon clock experiment, when it is inside an accelerating rocket what speed does it move at to keep up with it?
For example, if we scale this up and if we jump up and down like the photon in a moving train , how do we not end up at the end of the bus? Doesn't friction come into play when coming back down after reaching the top?
2. (Original post by Mystery.)
In the photon clock experiment, when it is inside an accelerating rocket what speed does it move at to keep up with it?
For example, if we scale this up and if we jump up and down like the photon in a moving train , how do we not end up at the end of the bus? Doesn't friction come into play when coming back down after reaching the top?
While we are in a uniformly moving train, we travel at the same speed as that of the train. So when we jump up we are still travelling at the same speed and we will continue to travel with that speed forever provided there are no resistant forces slowing us down.

But if the train is accelerating when we jump and fall back, the train will have reached a higher speed than the speed we had initially when we jump and so we would find ourselves fall back at the end of the train, for example.

Although this traces back to Newton's first law of motion, we can prove this law by pure reasoning with reference to relative motions.

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