Friction is created when two surfaces rub together; for example, when a car tyre moves over the road surface. Friction can create heat and smoke can often be seen coming from the tyres of racing cars. The friction between the road surface and the tyre causes the tread in the tyre to wear down. Placing something on a spinning wheel will cause friction to slow the wheel down; this is how brakes work.
Students could be asked to bring their bikes along to school one day and examine how their brakes work. Working in pairs, one student could lift the front wheel up by the handlebars while the other spins the wheel. They can then explore what happens as they slowly push the front brake. They could also consider what happens when it is pulled quickly. If possible, students could then have a go at cycling on different surfaces such as grass, tarmac or gravel and consider how easy it is to cycle on each of these. They could then draw conclusions about which surface created the most friction with the wheel.
Alternatively, students could use toy cars to explore the friction caused by different surfaces. A ramp could be created by propping a wooden board on a stack of books and covering it with different surfaces such as carpet, paper, sandpaper or wood. Students could record the time the car takes from the top to the bottom of the ramp. They could then use results to draw conclusions on the friction created by each surface.