At the conclusion of this chapter, the student should be able
- 1. Name, define, and use the following terms properly
as they apply to linear motion: force, inertia,
mass, weight, momentum, and impulse.
- 2. Explain what is meant by the terms magnitude,
direction, and point of application
of force, and use these terms properly as they apply to internal
and external forces.
- 3. Explain the effect of specified changes in the magnitude,
direction, and point of application of force on the motion state
of a body.
- 4. Define and give examples of the terms linear
forces, concurrent forces, and parallel
- 5. Determine the magnitude, direction, and point of application
of muscle forces in hypothetical situations in which specific muscles
are considered in isolation.
- 6. State Newton’s laws as they apply to linear motion.
- 7. Explain the cause and effect relationship between the forces
responsible for linear motion and the objects experiencing the motion.
- 8. Name and define the basic external forces responsible for
modifying motion: weight, normal reaction, friction, elasticity,
buoyancy, drag, and lift.
- 9. Draw and analyze simple two-dimensional free-body diagrams
in which all applicable external forces are properly accounted for.
- 10. Explain the work–energy relationship as it applies
to a body experiencing linear motion.
- 11. Define and use properly the terms work,
power, kinetic energy, and potential
- 12. Using the concepts that govern linear motion, perform
a mechanical analysis of a selected motor skill.
Objects start moving when they are pushed or pulled, that is,
when some type of force acts on them. Forces produce motion, stop
motion, and prevent motion. They may increase speed, decrease speed,
or cause objects to change direction. They may push or pull to cause
motion or produce a net effect so that bodies remain stationary. Force is defined as that which pushes or
pulls through direct mechanical contact or through the force of
gravity to alter the motion of an object. It is the effect
that one body has on another. The identification of forces that
act to produce motion of the body or of an object is an important
element of a kinesiological analysis.
The action of a force may be internal or external. Internal forces
are defined as forces exerted by bodies on other bodies within a
defined system, whereas external forces are those exerted by bodies
within an arbitrarily specified system on bodies outside the specified
system. Internal forces cause differences in body shape, and external
forces cause displacement of the body. In kinesiology, the system
under consideration is the human body. Internal forces are therefore
usually classified as muscle forces that act on the various structures
of the body, and external forces are those outside the body. The
best-known external force is weight, or gravitational force. Wind
or water resistance forces, friction, or forces due to other objects
acting on the body are also external forces.