Physics (university) · Part 03
Work, energy and momentum
Energy bookkeeping and collisions: what is conserved and how to use it.
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- WorkThe energy a force transfers when it moves something. Work is force times distance moved along the force, W = F d cos theta.
- Kinetic energyThe energy of motion, KE = 1/2 m v squared. Doubling speed quadruples it.
- Work-energy theoremThe net work done on an object equals its change in kinetic energy.
- Gravitational potential energyStored energy due to height, PE = mgh. It can turn into motion when the object falls.
- Conservation of energyEnergy is never created or destroyed. It changes form, and the total stays the same in a closed system.
- PowerHow fast energy is transferred, P = work / time. The unit is the watt, one joule per second.
- MomentumMass times velocity, p = mv. It has a direction, and the total in a closed system is conserved.
- ImpulseThe change in momentum caused by a force acting over time: F times time equals change in p.
- CollisionsMeetings where momentum is conserved. In elastic collisions kinetic energy is also kept. In inelastic ones some is lost.