another good'n
heres another great one, i know theanswer, but lets see what you lot think...
a man stood in a train facing the direction of travel fires a rifle at a target sat at the opposite end of the carriage.
another person on the train times the interval between him pressing the trigger (exactly) and the bullet hitting the target.
The train is moving at 120mph say.
Another observer, stood on the ground beside the track as the train goes past also times the interval between the chap pulling the trigger and the bullet hitting the target.
Are the times the observers record the same?
(Hint: This helps to prove that time is not after all constant!!)