# Length contraction depends on the distance of the object?

1. Oct 3, 2008

### Shukie

http://home.orange.nl/kuip3148/phys1.JPG [Broken]

Not exactly homework, but a problem I found in my lecture notes. The train is moving at a constant speed 0.5c. Question b asks what the length of the train will be then at t = -1. From what I understand, this suggests that length contraction depends on the distance the object is away from an observer? So at t = -5 the length contraction would be different?

Last edited by a moderator: May 3, 2017
2. Oct 3, 2008

### Staff: Mentor

It seems that this problem is asking about the visual appearance of length contraction as seen by a particular observer, not the actual measured length contraction--which is obtained after accounting for light travel time and is the same for all observers within a frame. The actual measured--not just "seen"--length contraction does not depend on distance from any particular observer, since it's not a simple visual effect.

3. Oct 3, 2008

### Shukie

Thanks for your answer. I'm just trying to visualize what is going on and so I made a drawing. Can you tell me if this is in any way resembles what is actually going on?

http://home.orange.nl/kuip3148/phys2.GIF [Broken]

The green line would be the length Bob observes, while the black thingy denotes the actual length of the train.

Last edited by a moderator: May 3, 2017
4. Oct 4, 2008

### Staff: Mentor

Redraw your diagram to show the worldlines of the front and rear of the train. They should be parallel, but not overlapping.