Science

Forces - Friction

We have introduced balanced and unbalanced forces.
Today we will look at one of these forces, Friction.
Friction is a very useful force, without friction life would be very difficult.

Try the following:
Now press them hard to together and rub.
What do you notice?
Was it easy to do?
Your hands got hot and it is quite hard to do. The reason is that your hands are rough and when you rub them together the friction between them causes heat.

Rough surfaces have more friction.

Now run your hand over a smooth surface. Is it easy to do?

Smooth surfaces have less friction.

In short friction is the force that slows moving objects and it causes things to get hot.

You are walking on the street and you walk onto ice. Does the friction between your shoes and the ice increase or decrease?

The friction between your shoes and the ice decreases (there is less friction) that is why your feet slip.
Why can ice skaters move on ice then?

Ice skaters wear special boots that have a sharp blade on the bottom of each boot. This blade cuts into ice when placed side on to the ice. This cutting increases the friction between the blade and the ice. They turn the blade forward and push to move.

Which surface has got the most friction between your shoes and it:
1. A dry wooden floor
2. A wooden floor that has got water spilled on it?

The dry wooden floor has got the most friction.
This is why people put signs up when floors are wet because there is less friction on the surface for your shoes to grip.

The brakes on a bike work by using friction. The rubber pad presses on the rim of the wheel and the friction slows down the wheel.
Do you expect the brakes to be hot or cold?

HOT, friction causes heat.

Sometimes we want to reduce friction. For example in a car engine many metal parts have to move past each other very quickly. These parts need to slide easily past each other.
What could we do to reduce friction and stop them rubbing?

1. We should ensure that the metal parts are smooth.
2. We use oil to make sure that the surfaces slide easy and cause less heat and they don't wear quickly.
(That is why is important to check the oil in an engine).
Well that is it for today.
I hope you found that easy and you understand the force of friction better.

Review

• Friction is a force between two surfaces;
• Smooth surfaces have less friction;
• Rough surfaces produce more friction;
• Friction causes heat;
• We can decrease (reduce) friction by using liquids to make surfaces smoother.

Next time we will look at the force of gravity.