AP Physics 1 · Summary

Unit 3 summary

1. Work by a constant force is $W = Fd\cos\theta$. Perpendicular forces do no work; forces against the motion do negative work.
2. Kinetic energy is $\tfrac{1}{2}mv^2$, and the net work equals the change in kinetic energy.
3. The work done by a changing force is the area under its force-position graph.
4. Potential energy belongs to a system: $\Delta U_g = mg\Delta y$ and $U_s = \tfrac{1}{2}kx^2$. Only changes matter, so put the zero anywhere.
5. With no friction and no outside work, $K + U$ stays constant; with friction, the missing mechanical energy becomes thermal energy, $f_kd$.
6. Kinetic and potential energy do not depend on the direction of motion, so an energy equation never needs the angle at which an object is moving.
7. Power is energy per time, $P = \Delta E/\Delta t$, and $P = Fv$ for a force along the motion.