Forces can make things move. They can also act on stationary objects without causing motion. Sometimes we use a force on an object that is already moving, to stop it. A train uses a braking force as it approaches a station. Similarly, when astronauts were about to land on the moon, rockets were used to slow down their craft, so it could make a soft landing. Forces can also change the direction of motion. This happens in baseball when a batter hits the ball. The ball is first slowed down, then stopped for an instant, then shot off in a different direction.
The Force Of Gravity
This is the force that pulls objects down to the ground. when we say a rock is heavy, we mean that the force of gravity pulling down on it is a strong force. To lift the rock off the ground, you must use a force that is slightly greater than the pull of gravity. Once the rock is moving upwards, the lifting force becomes equal to the gravity force. The force of the Earth's gravity is what holds the moon in its nearly circular path around the Earth and prevents it from flying off into outer space. Similarly, it is the force of the sun's gravity that keeps the Earth and the other planets in their orbits.
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