Eight of us go fourth, not back, to protect our king from an attack. What are we?

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

I look at you, you look at me I raise my right, you raise your left. What am I?

What goes through cities and fields, but never moves?

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

What work can one never finish?

What jumps when it walks and sits when it stands?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?