Friction

"kelaskita.com" 

 Friction is the force between two surfaces rubbing together. Here are some very simple facts:
When two smooth surfaces rub together there is very little friction.
When two rough surfaces rub together there is more friction.
There is less friction when there is a liquid (e.g. oil) between the two surfaces.
There is more friction if the two surfaces are forced against each other.

Friction is a good thing:
Just think of walking on a wet marble floor or an icy pavement with new leather soled shoes: you might slip over! Worse still, if the tyres on your car are worn out and the road is wet and slippery, you will probably skid the car and have an accident. Both your shoes and the car's tyres need good grip so their surfaces are rough. This increases the friction between them and the ground.

Friction is also very important for your car's brakes to work properly. When you put you foot on the brake pedal, some rough pads are squeezed tight against the brake discs. This friction slows the car down. If oil gets on the discs, the brakes will not work so well.

Friction is a bad thing:
Friction inside a car engine and inside the wheel axles will slow a car down and wear out the metal. To prevent this we put oil or even grease in them. This makes their surfaces more slippery and so reduces friction.

I hope that you will be able to remember most of the facts on this page, but you must memorise the definition of a balanced diet. Write it on a small index card. Put the red words on one side of the card and the blue ones on the other. Add the card to your revision pack.

Friction is the force between to surfaces rubbing together. It is high if the surfaces are dry and rough and it is low if the surfaces are smooth and wet. 

"Life Is a Learning"