\section{Work, Energy, and Power} In this unit, we develop the energy viewpoint for mechanics. We begin with work as the accumulated effect of a force acting through a displacement, using the line-integral form $W=\int \vec{F}\cdot d\vec{r}$ as the calculus backbone and then connecting net work to changes in kinetic energy $K$. We then shift to conservative forces and potential energy $U$, which lets us track mechanical energy with $E_{\mathrm{mech}}=K+U$. With that accounting framework in place, we finish by defining power $P$ as the rate at which energy is transferred or transformed. The emphasis throughout stays on AP-level mechanical energy, including one-dimensional potential-energy graphs and clear bookkeeping of energy changes. \input{concepts/mechanics/u3/m3-1-work.tex} \input{concepts/mechanics/u3/m3-2-work-energy.tex} \input{concepts/mechanics/u3/m3-3-potential-energy.tex} \input{concepts/mechanics/u3/m3-4-energy-conservation.tex} \input{concepts/mechanics/u3/m3-5-power.tex}