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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