An explanation of friction that uses a bobsleigh as an example. A force is needed to start an object moving and to stop it once it is moving. A force can make an object speed up or slow down. Friction is a force generated when surfaces move across each other.
Students could be shown images of different materials under the microscope and try to guess what they are. What are the defining features? Students could go on to test which of these materials generate the most friction by attaching samples to the bottom of their shoes and sliding along a slippery floor. How do students think the microscopic features of these materials affect the amount of friction generated?
Alternatively, students could investigate and create their own bobsleigh using different materials to find out which combination of materials work the best. They could run their own bobsleigh competition to determine which design is the most effective.