Relativity Thought Experiment

[Shark 774]

If I travel away from Earth at 0.7c, relative to the Earth and my friend travels in the opposite direction at 0.7c, relative to the Earth, what speed to I measure him to be travelling at, relative to myself???

[DrGreg]

\frac{0.7 + 0.7}{1 + 0.7 \times 0.7}\,c

Velocity-addition formula (http://en.wikipedia.org/wiki/Velocity-addition_formula)