Physics Quiz

A steel rod is built from the Earth to the Sun. Suddenly the end near the Earth is pushed forward 1 meter. The other end of the rod therefore must move 1 meter, but isn't this a violation of the principle that no signal can travel faster than the speed of light c? After all, it takes light 500 seconds to travel the Earth-Sun distance.

Is this a way to send signals faster than c?

A tank approaches a trap (hole in the ground). Because it is moving very fast compared to c, the speed of light, the driver in the tank sees the trap approaching very fast; according to the length contraction effect of relativity, the driver sees the hole as very narrow (left picture). However, in the rest frame of the trap, the tank appears to be foreshortened, and so the trap is large enough for the tank to fall into.

Does the tank fall into the trap?

A book is standing on end. You throw a super ball at it, and the ball bounces off. You then throw some chewing gum with the same mass as the ball and at the same speed and height; the gum sticks to the book. In which situation is it more likely that the book will tip over:

Will the book tip more readily if hit by the ball or by the gum?

A child is sitting in a car (with closed windows) holding onto a string tied to a floating balloon. The car accelerates forward, so the child is pressed back into the seat. What does the balloon do?

Does the balloon go forward, backward, or neither?