1. Feb 25, 2015

Quarlep

Lets suppose we used Einstein Velocity Addition equation and we found a result this is the same for every observer isnt it ?

2. Feb 25, 2015

Staff: Mentor

I'm having some trouble understanding your question. What exactly do you expect to be the same for all observers?

3. Feb 25, 2015

Quarlep

An observer O observer o observes two objects letc call them a and b ad their speed a 0.5c and b 0 c so relative velocity is 0.5c İts for observer a than lets suppose theres another observer I am asking this another observer et call z will calculate relaitve speed 0.5 isnt it ? (Relative speed between A and B)

4. Feb 25, 2015

HallsofIvy

Yes. If observers x and y both observe objects A and B, determine the speeds of A and B relative to themselves, then calculate the speed of A relative to B, they will get the same answer.

5. Feb 25, 2015

Staff: Mentor

If A is moving at .5c relative to B, then A will be moving at .5c relative to all observers at rest relative to B.

If B is moving at some non-zero speed q relative to some third observer Z, then A's speed relative to Z will not be q+.5c and Z's measurement of the difference between the speed of A and B will not be .5c.

6. Feb 25, 2015

Staff: Mentor

Have you tried calculating it yourself? Suppose observer z is traveling at velocity 0.25c relative to observer o. Let va' and vb' be the velocities of a and b relative to z.

(a) What do you get for va' and vb' ?

(b) What do you get for the relative velocity vab' = (va' - vb') / (1 - va'vb'/c2) ?

Last edited: Feb 25, 2015