YBM wrote:
The following describes a very elegant and simple derivation of the
relativistic
formula for the addition of velocities, w = (u+v)/(1 + uv/c^2).

It is due to David Mermin.

See:
http://dorigo.wordpress.com/2008/04/...ivistic-train/


What about this one?

In S1, a body is moving with the speed u = dx/dt.
What is its speed w = dx'/dt' in S2 which is
moving with the speed -v relative to S1?

dx' = g(dx + v*dt)
dt' = g(dt + (v/c^2)*dx)

w = dx'/dt' = (dx + v*dt)/(dt + (v/c^2)*dx)
w = (dx/dt + v)/(1 + (v/c^2)*(dx/dt))
w = (u + v)/(1 + u*v/c^2)

--
Paul

http://home.c2i.net/pb_andersen/