# Length contraction depends on the distance of the object?

1. Oct 3, 2008

### Shukie

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?

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?

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

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.