Introduction to Sports Biomechanics: Analysing Human Movement ...

INTRODUCTION TO SPORTS BIOMECHANICS
performer is evenly distributed about this point. The motion of the centre of mass
of an object, including the sports performer, totally specifies the linear motion of the
object as a whole, even if the object’s overall motion is more general. Linear motion
ignores any rotation about the centre of mass, which means that it only tells us part,
often only a very small part, of the movement pattern we are studying. Linear motion
is sometimes known as ‘translation’, but we will use ‘linear motion’ throughout this
book.
Rotation and rigid bodies – the ‘rigid body’ model
Figure 3.4 Angular motion.
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Rotation, or angular motion, is motion in which all parts of an object travel through
the same angle in the same time in the same direction about the axis of rotation. The
movement of a body segment about a joint, as in Figure 3.4, is motion of this type. An
object that retains its geometrical shape, for example a cricket bat, can be studied in this