Work and Energy
Work: W = F × d × cos(θ). Only the force component parallel to motion does work. Carrying a weight horizontally across a level floor at constant height does no work — force (upward) is perpendicular to motion (horizontal). Measured in joules (J).
Kinetic energy (KE): KE = ½mv². Doubling speed quadruples KE; tripling speed increases KE by 9×.
Gravitational potential energy (PE): PE = mgh. Depends on mass, gravity, and height above a reference point.
Conservation of energy: In the absence of friction, PE + KE = constant. A ball dropped from height h converts all PE to KE just before impact: mgh = ½mv².
Power: P = W / t = F × v. Rate of doing work. Measured in watts (W). 1 horsepower = 746 W.