Machines 2. Friction

Friction is a force that resists, or works against, motion

Vocabulary: friction a force that works against motion when one object rubs against another object

Every motion that takes place on Earth is affected by friction Without friction, life would be very different

You could not walk without friction to keep your feet from sliding on the ground

Concrete, grass, and dirt are rough surfaces Rough surfaces provide more friction than smooth surfaces

If you have ever tried to walk on ice, you know that your feet slip and slide

Smooth surfaces such as ice provide very little friction

Without friction, you could not pick things up or hold them Everything you tried to hold would slip through your hands and fall

Without friction cars could not move Their tires would not hold on to the road

Mud does not provide enough friction for the tires to hold When a car gets stuck in mud, the wheels turn around but the car does not move Mud does not provide enough friction for the tires to hold

Have you ever tried to push a heavy box?

Friction between the ground and the box makes this difficult You can make the box easier to push by taking some things out of the box

This makes the box lighter The heavier something is, the more friction slows it down

Try rubbing your hands together Friction makes heat Try rubbing your hands together

You will feel them getting warmer

When you rub two sticks together, they get warmer and warmer When they get hot enough, they start to burn