Rotational Motion
Rotational Motion
Until 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.
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