Rotational kinematics

The skill

Rotation about a fixed axis uses the same three constant-acceleration equations as straight-line motion, with $\theta$, $\omega$ and $\alpha$ in place of $x$, $v$ and $a$, and you choose among them the same way. To move between the wheel and a point on it, use $\mathrm{\Delta }s=r\mathrm{\Delta }\theta$, $v=r\omega$ and $a_T=r\alpha$, which only work with angles in radians. Every point on a rigid wheel shares the same $\omega$, but points farther out move faster. Students lose answers by leaving revolutions unconverted; one revolution is $2\pi$ radians.