Uses of Motors
Many machines and devices contain electric motors that may not be
as obvious as the motor that turns the blades of a fan, for example.
Even though the motion produced by the motor is circular, motors
can move objects in any direction. For example, electric motors move
power windows in a car up and down.
Motors can be very large, such as the motors that
power an object as large as a subway train. They draw
electric current from a third rail on the track or wires
overhead that carry electric current. A car uses an
electric current to start the engine. When the key is
turned, a circuit is closed, producing a current from the
battery to the motor. Other motors are very small, like
the battery-operated motors that move the hands of
a wristwatch.
Motor B moves
a laser across
the CD.
These gears change
the rotational motion
of the motor into a
straight motion.
laser
Motor A
turns the CD.
Check Your Reading
The illustration on the left shows the
two small motors in a portable CD player.
Motor A causes the CD to spin. Motor B
is connected to a set of gears. The gears
convert the rotational motion of the
motor into a straight-line motion, or
linear motion. As the CD spins, a laser
moves straight across the CD from the
center outward. The laser reads the
information on the CD. The motion
from Motor B moves the laser across
the CD.
Explain the function served by each motor in a CD player.
KEY CONCEPTS
CRITICAL THINKING
1. Explain how electric current and
magnetism are related.
4. Contrast How does an
electromagnet differ from
a permanent magnet?
2. Describe three uses of
electromagnets.
3. Explain how electrical energy
is converted to motion in
a motor.
542 Unit 4: Electricity and Magnetism
5. Apply Provide examples of
two things in your home that
use electric motors, and
explain why they are easier to
use because of the motors.
CHALLENGE
6. Infer Why is it necessary
to change the direction of
the current in the coil of an
electric motor as it turns?