After completing this chapter, you
will be able to:
- Discuss the interrelationships among kinematic variables.
- Correctly associate linear kinematic quantities with their
units of measure.
- Identify and describe the effects of factors governing projectile trajectory.
- Explain why the horizontal and vertical components of projectile
motion are analyzed separately.
- Distinguish between average and instantaneous quantities,
and identify the circumstances under which each is a quantity of
- Select and use appropriate equations to solve problems related
to linear kinematics.
Why is a sprinter’s acceleration close to zero in the
middle of a race? How does the size of a dancer’s foot
affect the performance time that a choreographer must allocate for
jumps? At what angle should a discus or a javelin be thrown to achieve
maximum distance? Why does a ball thrown horizontally hit the ground
at the same time as a ball dropped from the same height? These questions all
relate to the kinematic characteristics of a pure form of movement:
linear motion. This chapter introduces the study of human movement
mechanics with a discussion of linear kinematic quantities and projectile
Kinematics is the geometry, pattern,
or form of motion with respect to time. Kinematics, which describes
the appearance of motion, is distinguished from kinetics, the forces
associated with motion. Linear kinematics involves the shape, form,
pattern, and sequencing of linear movement through time, without
particular reference to the forces that cause or result from the
Careful kinematic analyses of performance are invaluable for
clinicians, physical activity teachers, and coaches. When people
learn a new motor skill, a progressive modification of movement
kinematics reflects the learning process. This is particularly true
for young children, whose movement kinematics changes with the normal
changes in anthropometry and neuromuscular coordination that accompany
growth. Likewise, when a patient rehabilitates an injured joint,
the therapist or clinician looks for the gradual return of normal
Kinematics spans both qualitative and quantitative forms of analysis.
For example, qualitatively describing the kinematics of a soccer
kick entails identifying the major joint actions, including hip flexion,
knee extension, and possibly plantar flexion at the ankle. A more
detailed qualitative kinematic analysis might also describe the
precise sequencing and timing of body segment movements, which translates
to the degree of skill evident on the part of the kicker. Although
most assessments of human movement are carried out qualitatively
through visual observation, quantitative analysis is also sometimes
appropriate. Physical therapists, for example, often measure the range
of motion of an injured joint to help determine the extent to which
range of motion exercises may be needed. When a coach measures an
athlete’s performance in the shot put or long jump, this too
is a quantitative assessment.
Sport biomechanists often ...