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Definition: Rigid Body
A rigid body is one that does not deform during its motion.
distance between any two points in the rigid body remains
Idea: Angles to Describe Rotation
In order to completely describe the rotation of a rigid body about a fixed axis, O , it is sufficient to give the angle, , between the position vector of any point in the rigid body (for example the point P in the Fig. 7.1), and some arbitrary, fixed reference line.
The angle expressed in radians is defined as the ratio of the arc length, s , swept out by the angle, to the radius, r , of the corresponding circle:
|radians = .||(1)|
Note: For a complete revolution, s = 2r is the circumference, so that the conversions between revolutions, radians and degrees are given by:
|1 revolution = 2 radians = 360 degrees.||(2)|
|1 radian = 360/2 degrees = 57.3 degrees.||(3)|