AP Physics 1 · Summary

Unit 2 summary

1. Choose a system first; only external forces change the motion of its center of mass.
2. Draw every real force with its source: weight, normal, tension, friction, spring. Never draw a separate centripetal force.
3. $\vec F_{\text{net}} = m\vec a$: zero net force means constant velocity, which is not always rest.
4. Third-law partners are equal in size, opposite in direction, and act on different objects.
5. Weight is $mg$ with $g = GM/R^2$, and gravity falls off as $1/r^2$ with distance from the center.
6. Kinetic friction is $\mu_kF_N$; static friction is whatever is needed, up to $\mu_sF_N$. A spring pulls back with $kx$.
7. In circular motion the forces toward the center add to $mv^2/r$, with $v = 2\pi r/T$.