It is a warm summer's day. The birds are chirping in the air. And you are walking down the street, whistling away. You find a pebble by the side and throw it up. It falls back onto the ground. Why did this happen?
- What goes up, must come down.
- The ground is the natural resting place for a pebble.
- Your gentle throwing hasn't given the pebble enough kinetic energy to escape the Earth's gravity