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 = \frac{1}{2}$$mv^2 = p^$\frac{2}{2m}$) is always non-negative. Potential Energy exists only for conservative forces: gravitational (U = mgh) and elastic (U = \frac{1}{2}$$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 = $\frac{dW}{dt}$ = 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.