Friction and Its Kinds
The quiet force that lets you walk, and slowly wears machines out
Big Idea: Whenever one surface touches another, a force called friction appears. It always pushes against the motion (or the attempted motion). Friction can be a helpful friend that stops you slipping, or an annoying enemy that heats up and wears down machines.
By the end you will be able to:
- say what the friction force is and which way it points,
- name the three kinds: static, sliding and rolling friction,
- use the formula Ffr = μN and explain every symbol,
- explain what friction depends on (and what it does not),
- give examples of useful and harmful friction, and ways to change it.