After completing this chapter, you
will be able to:
- Distinguish angular motion from rectilinear and curvilinear
- Discuss the relationships among angular kinematic variables.
- Correctly associate angular kinematic quantities with their
units of measure.
- Explain the relationships between angular and linear displacement,
angular and linear velocity, and angular and linear acceleration.
- Solve quantitative problems involving angular kinematic quantities
and the relationships between angular and linear kinematic quantities.
Why is a driver longer than a 9-iron? Why do batters slide their
hands up the handle of the bat to lay down a bunt but not to drive
the ball? How does the angular motion of the discus or hammer during
the windup relate to the linear motion of the implement after release?
These questions relate to angular motion, or rotational motion
around an axis. The axis of rotation is a line, real or imaginary,
oriented perpendicular to the plane in which the rotation occurs,
like the axle for the wheels of a cart. In this chapter, we discuss
angular motion, which, like linear motion, is a basic component
of general motion.
Understanding angular motion is particularly important for the
student of human movement, because most volitional human movement
involves rotation of one or more body segments around the joints
at which they articulate. Translation of the body as a whole during
gait occurs by virtue of rotational motions taking place at the
hip, knee, and ankle around imaginary mediolateral axes of rotation.
During the performance of jumping jacks, both the arms and the legs
rotate around imaginary anteroposterior axes passing through the
shoulder and hip joints. The angular motion of sport implements
such as golf clubs, baseball bats, and hockey sticks, as well as
household and garden tools, is also often of interest.
As discussed in Chapter 2, clinicians, coaches, and
teachers of physical activities routinely analyze human movement
based on visual observation. What is actually observed in such situations
is the angularkinematics of human movement. Based on observation
of the timing and range of motion (ROM) of joint actions, the experienced
analyst can make inferences about the coordination of muscle activity
producing the joint actions and the forces resulting from those
Much of the reported description of the developmental stages
of motor skills is based on analysis of angularkinematics. For
example, three developmental stages for kicking among children age
2–6 have been identified (2). In stage 1, the
child kicks using a small ROM of hip flexion, with no coordinated
motion apparent at any other joint. In stage 2, knee extension is
coordinated with hip flexion, and the arms are abducted at the shoulders
to promote balance. Stage 3 is characterized by increased hip flexion
and knee extension, and elbow flexion is present in addition to
shoulder abduction to improve balance. The knowledgeable analyst
can obtain a great deal of information about the ...