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Technology: Engineering Our World
Gears, like pulleys, are modified levers. They transmit rotary motion.
They increase or decrease speed, change the direction of motion, or
transmit a force. See Figure 8-36. This force, known as torque, acts at a
distance from the center of rotation. To understand this concept more
easily, think of torque as a measure of turning effort. It is similar to using
a wrench to tighten a bolt. See Figure 8-37 and Figure 8-38.
An effort (E) is applied at a distance (R) from the center of the nut.
The torque on the nut is calculated by multiplying the effort (E) by the
distance (R). The applied force is mea sured in pounds (newtons) and the
distance from the center of rotation is measured in feet. Therefore, torque
is measured in ft.-lb. In the metric system, the applied force is measured
in newtons, the distance from the center of rotation is measured in meters,
and torque is measured in newton-meters
(N•m).
As you look at a gear, you can consider the center of the gear to be like
the nut. Consider the end of the gear tooth to be like the end of the wrench.
Effort
Radius
Torque
gure 8-37. Torque is force applied to a
radius.
E
gure 8-38.
wrench turning a nut. How is the gear similar
to the wrench?
gure 8-36. Gears are similar to pulleys, except they have teeth that
prevent them from slipping.