When a tennis ball hits the ground, a ........... changes its shape, speed, and direction.

The............ ......., or force of gravity, is the force that attracts you to the Earth.

If the resultant force is zero the forces are .............. .

If the resultant force is not zero the forces are ............ .

.............. is a force that slows down moving objects.

Cyclists put oil on the axles of their bicycle to reduce friction. This is called .............. .

There is a force between all objects

called the force of ............. . This force is pulling you down towards the center of the Earth.

When an object moves through air, there is a force on it called ..... ............ .

Air resistance is less if the area in contact with the air is reduced. ..................... reduces air resistance by changing the flow of air over a car or plane.

When a parachutist jumps out of a plane she accelerates because of the force of gravity acting on her. As she speeds up the air resistance increases until it balances her weight. She then falls with a steady speed called the ........ ............ .