Power

Work tells you how much energy gets transferred. Power tells you how quickly that transfer happens. Average power is just work divided by time, P = W/t, measured in watts, where one watt is one joule per second. Two cars can burn the same tank of gas and deliver the same total work to the road, yet the one with the more powerful engine reaches highway speed sooner, because it pushes that energy out faster.

Power connects directly to force and velocity. Since W = F d (for a constant force along the direction of motion), dividing by time gives P = F (d/t) = F v. This instantaneous form matters because velocity rarely stays constant: a car accelerating from a stoplight needs rising power even at constant force, since v is climbing. If the engine instead holds power constant, the force it can deliver must fall as speed rises, which is why cars feel like they run out of push at high speed even with the pedal flat to the floor.

This sits right after work and energy because power is just the time derivative of the work-energy story: W is the integral of F dx, and P = dW/dt is what you get by watching that integral unfold in time. In the next stretch of the unit, power shows up again whenever you need to connect a force-time relationship to energy delivered, especially in problems with motors, engines, or anything climbing against gravity at a steady rate.