Forces at Work

Put a ball on the table so that it keeps still. If i don't touch it, it will stay where it is, and it will only start to move when i push it. A cart will stay on a flat place until a horse or tractor pulls it, then it starts moving. These pulls and pushes are called forces, and forces make things move. They can also all things down and stop them moving. When i put on the brakes on my bicycle, me airs applying forces to the wheels, which try to stop them moving.

In general, things are still stay still, and things that are moving stay moving, and it is hard to make them change. I say that they have inertia. I can use a big bowl full of water to show inertia. Put it on the ground outside and suddenly push the bowl hard. I will find that bowl moves, but the water inside stays there. Then what happens?

When i roll a table-tennis ball gently along the carpet, i find that it goes so far and then stops. Some force must be making it slow down. It is a force i call friction. There is friction when any objects moves and rubs against another. Rough surfaces have a lot of friction; Try rolling your ping-pong ball along a smooth floor to see how far it goes.

Friction also makes heat. I can find this out by rubbing my hands together.