Rotational variables
In this chapter we will be dealing with the rotation of a rigid body about a fixed axis. Every point
of the body moves in a circle, whose center lies on the axis of rotation, and every point
experiences the same angular displacement during a particular time interval.
Figure 11.1. Relation between s and [theta].
Suppose the zaxis of our coordinate system coincides with the axis of rotation of the rigid body.
The xaxis and the yaxis are taken to be perpendicular to the zaxis. Each part of the rigid body
moves in a circle around the zaxis. Suppose a given point A on the body covers a linear distance
s during the rotation (see Figure 11.1). During one complete revolution point A covers a distance
equal to 2[pi]r. In that case, the angle of rotation is equal to 2[pi] radians. For the situation shown
in Figure 11.1, the angle of rotation can be easily calculated:
In describing the rotation of a rigid body we have to choose a reference line with respect to
which the angle of rotation is being measured. In figure 11.1 the reference line connects the
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 Fall '09
 Angular Momentum, Rotation, Angular velocity, Euclidean geometry

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