If Keiji stands at the base of a hill and throws a ball straight up into the air, what happens to the ball after Keiji lets go, and why? Respond very briefly.
The ball goes up for a moment, slows down, and then falls back down the hill toward Keiji. This happens because when Keiji throws the ball, it initially has upward momentum. However, gravity acts on the ball, pulling it back toward the Earth. As it goes up, it slows down because the force of gravity is working against its upward motion. Once it stops, gravity causes it to accelerate back down toward the ground. It lands back down the hill because gravity acts on it vertically, pulling it straight down, not at an angle to or away from the hill.