Introduction to SAT II Physics - FreeExamPapers

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.
Important Definitions
There are a few basic physical concepts that are fundamental to a proper understanding of
rotational motion. With a steady grasp of these concepts, you should encounter no major
difficulties in making the transition between the mechanics of translational motion and of
rotational motion.
Rigid Bodies
The questions on rotational motion on SAT II Physics deal only with rigid bodies. A rigid body is
an object that retains its overall shape, meaning that the particles that make up the rigid body stay
in the same position relative to one another. A pool ball is one example of a rigid body since the
shape of the ball is constant as it rolls and spins. A wheel, a record, and a top are other examples of
rigid bodies that commonly appear in questions involving rotational motion. By contrast, a slinky
is not a rigid body, because its coils expand, contract, and bend, so that its motion would be
considerably more difficult to predict if you were to spin it about.
Center of Mass
The center of mass of an object, in case you have forgotten, is the point about which all the matter
in the object is evenly distributed. A net force acting on the object will accelerate it in just the
same way as if all the mass of the object were concentrated in its center of mass. We looked at the
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