this chapter, we have focused
almost entirely on translational motion
the motion of bodies moving through space. But there is a second
kind of motion, called rotational motion
, which deals
with the rotation of a body about its center of mass. The movement
of any object can be described through the combination of translational motion
of the object’s center of mass and its rotational motion about that
center of mass. For example, look at the diver jumping into the
water that we saw in the previous chapter.
The diver’s translational motion is the parabolic
trajectory of her center of mass. However, if that were the only
motion of the diver’s body, diving competitions would be considerably
more boring. What astonishes fans and impresses judges is the grace and
fluidity of the rotational motion of the diver’s arms, legs, feet,
etc., about that center of mass.
You will find that rotational motion and translational
motion have a lot in common. In fact, aside from a few basic differences,
the mechanics of rotational motion are identical to those of translational
motion. We’ll begin this chapter by introducing some basic concepts that
are distinct to rotational motion. After that, we will recapitulate
what we covered in the chapters on translational motion, explaining
how the particularities of rotational motion differ from their translational
counterparts. We will examine, in turn, the rotational equivalents
for kinematic motion, dynamics, energy, and momentum.
There will be at most one or two questions on
rotational motion on any given SAT II test. On the whole, they tend
to center around the concepts of torque and equilibrium.