Friction is a force that slows down two materials which are moving past each other and touching.
If you rub your hands together, they will become warm. This is because of friction.
We looked at air resistance last week: this is a type of friction because there are two materials moving past each other and touching.
1. What two materials were moving past each other?
Bumpy or rough surfaces have more friction than smooth surfaces, when they move against something.
2. Think of, or find, something that has been made rough or bumpy so that is has more friction.
3. Think of, or find, something that is very smooth, and so has less friction.
4. When might you want lots of friction?
5. When might you not want much friction?