Work, Energy, and Power provide a scalar framework for analyzing motion, complementing Newton's vector-based Laws. Work W = F.s*cos(theta) measures energy transfer by a force. The Work-Energy Theorem (W_net = delta_KE) is the central result, relating net work to kinetic energy change.

Kinetic Energy (KE = (1/2)mv^2 = p^2/(2m)) is always non-negative. Potential Energy exists only for conservative forces: gravitational (U = mgh) and elastic (U = (1/2)kx^2). Conservation of mechanical energy (KE + PE = constant) holds when only conservative forces act.

For non-conservative forces like friction: W_nc = delta(KE + PE). Friction always dissipates energy as heat. Power (P = dW/dt = F.v) measures the rate of doing work, with units of Watts.

Collisions apply conservation of momentum (always) and energy (only if elastic). Elastic collisions conserve KE; perfectly inelastic collisions maximize KE loss. The coefficient of restitution e = relative speed of separation / relative speed of approach characterizes the collision type.

Key problem-solving strategy: use energy when relating speeds at different points (avoiding path details); use Newton's Laws when forces and accelerations are needed.