# Time dilation question

tomz
Hello

When we try to find a formula for time dilation, we think of a situation where the velocity of the other frame is perpendicular to the velocity of the light

(http://en.wikipedia.org/wiki/Time_dilation)

Why is this? I know if we try any other direction there is length contraction involve. But the proof of length contraction goes after that right?

why not derive the formula for time dilation by considering a situation where the frame and the light goes in the same direction and then think there is a 'length expansion' for all object in the other 2 dimensions other than the direction of travel (relative to us)?

Homework Helper
Hello

When we try to find a formula for time dilation, we think of a situation where the velocity of the other frame is perpendicular to the velocity of the light

(http://en.wikipedia.org/wiki/Time_dilation)

Why is this?
Because it makes the math easier for beginning students to do the derivation. It does not matter what the angle is, it's always the same.
I know if we try any other direction there is length contraction involve. But the proof of length contraction goes after that right?
Also see: "Michealson-Morely experiment".

why not derive the formula for time dilation by considering a situation where the frame and the light goes in the same direction and then think there is a 'length expansion' for all object in the other 2 dimensions other than the direction of travel (relative to us)?
Because it is much much easier to do it this way around.
Give it a go and see :D