Friction
Friction is an everyday force that arises from two surfaces interacting. When these surfaces slide against each other, this interaction increases the thermal energy of the two surfaces (the temperature goes up). While it is easy to think of friction as a 'bad' thing, friction is needed in order to drive (it's what pushes the wheels on our car forward and allows us to stop and turn), or even walk.
Friction is why:
- brake rotors get hot when stopping or slowing down,
- rubbing pieces of wood together can start a fire (see 7 methods of primitive fire starting),
- rubbing hands together to make them warm.
Friction in engines and machines contributes to losses of useful energy, which also wears out the parts in a car (hence the need for lubricating oil). This means that friction is taking the large (macroscopic) motion of an object and turning it into the small (microscopic) motion of atoms and molecules. Friction is a non-conservative force meaning the energy becomes less useful (but doesn't disappear from the universe, see conservation of energy).
There are three types of friction:
- Static friction, when surfaces don't move with respect to each other, like shoes on a floor while walking, or tires on the road while driving.
- Kinetic friction, when surfaces move with respect to each other like shoes on a banana peel, or skidding tires on a road.
- Rolling friction, which is also known as rolling resistance.
For a more complete description of physics please consult hyperphysics.
Phet Simulation
The University of Colorado has graciously allowed us to use the following Phet simulation. This simulation explores how friction makes macroscopic kinetic energy becomes microscopic kinetic energy: