Friction and resistance

What are friction and resistance?

Friction is a force, the resistance of motion when one object rubs against another.

Whenever two objects rub against each other, they cause friction. Friction works against the motion and acts in the opposite direction. The amount of friction depends on the materials from which the two surfaces are made. The rougher the surface, the more friction is produced. For example, you would have to push a book harder to get it moving on a carpet than you would on a wooden floor. This is because there is more friction between the carpet and the book than there is between the wood and the book.

One kind of friction or resistance is air resistance. Air resistance occurs between the surface of a falling object and the air that surrounds it and it also works to slow the rate at which the object falls. Air resistance works with surface area, so the more surface area, the more air resistance. Think about when you drop two pieces of paper: one crumpled and one flat. The crumpled one falls faster because there is less air resistance acting on the paper.

Friction can be useful. For example, friction between our shoes and the floor stop us from slipping and friction between tyres and the road stop cars from skidding.

Friction is sometimes unhelpful. For example, if you don't lubricate your bike regularly with oil, the friction in the chain and axles increases. Your bike will be noisy and difficult to pedal.

When there is a lot of friction between moving parts, energy is lost to the surroundings as heat. Think of what happens when you rub your hands together quickly. The friction warms them up.

Top 10 facts

1. Although wheels are great for rolling and reducing friction, they couldn't work without friction.
2. It would be really tough just to stand up without friction.
3. Friction can generate static electricity.
4. The harder two surfaces are pressed together, the more force it takes to overcome the friction and get them to slide.
5. Fluid friction is used a lot in water parks so we can slide smoothly and fast down giant slides.
6. Racing cyclists crouch down low on their bikes to reduce the air resistance on them. This helps them to cycle faster. They also wear streamlined helmets. These have special, smooth shapes that allow the air to flow over the cyclist more easily.
7. Ice causes very little friction, which is why it is easy to slip over on an icy day. However this is a good thing for ice skating and sledging.
8. When there is a lot of friction between moving parts, energy is lost to the surroundings as heat. When you rub your hands together quickly the friction warms them up.
9. Slippery substances such as oil reduce the friction between two surfaces. This is known as lubrication.
10. Have you ever felt as though you were walking in place when you were trying to walk into a strong wind? The air resistance is working against the force applied by your legs opposing motion and reducing acceleration.