"vector" <misturn@gmail.com> wrote in message 
news:1130132219.730964.45620@o13g2000cwo.googlegroups.com...
| how to show that in the direction perpendicular to the relative
| velocity between two reference frames there is no any contraction or
| expansion.notes:please deduce from the two principles of the theroy of
| special relativity.

v = dx/dt
cos(pi/2) = cos(90 degrees) = 0.
cos(pi/2).v = dy/dt = 0.

xi  = (x-vt)/sqrt(1- 0.vē/cē) = (x-vt)/1
tau = (t-vx/cē)/sqrt(1-vē/cē)
    = (t-vēt/cē)/sqrt(1-vē/cē)
    = t(1-vē/cē)/sqrt(1-vē/cē)
    = t*sqrt(1-vē/cē)
    = t*sqrt(1-0.vē/cē)
    = t*sqrt(1)
    = t
Einstein did not know the difference between speed and velocity.
Androcles.