AP Physics 1 · Summary

Unit 4 summary

1. Momentum $p = mv$ is a vector: pick a positive direction and give every velocity a sign.
2. Net impulse equals change in momentum: $F_{\text{net}}\Delta t = \Delta p$. On a force-time graph, the impulse is the area, negative below the axis.
3. For the same change in momentum, a longer contact time means a smaller average force.
4. Internal forces cancel in pairs; only a net external force changes a system’s total momentum. With none, total momentum is conserved, one direction at a time.
5. Every collision with no net outside force conserves momentum; only elastic ones also keep the total kinetic energy the same.
6. Objects that stick together move at the center-of-mass velocity, and that collision loses the most kinetic energy.