Friction in Depth: Static, Sliding and Rolling
Why surfaces grip, slip and roll — and how to put numbers on it
Big idea: Friction is the force that acts along the surface where two bodies touch. It always opposes relative sliding (or the tendency to slide). In Grade 10 we move past "friction is a nuisance" and treat it quantitatively: static friction that adjusts itself up to a maximum, sliding (kinetic) friction that stays roughly constant, and rolling friction that is far smaller than either. All three are governed by simple laws linking the friction force to the normal force through a coefficient of friction.
By the end of this topic you will be able to:
- distinguish static, sliding and rolling friction and rank their sizes,
- use fs ≤ μsN and fk = μkN correctly,
- find the normal force on a horizontal surface and on an incline,
- solve inclined-plane problems, including the angle of repose tan θc = μs,
- explain where engineers fight friction and where they need it.