Chapter 8 Machines
243
Gears
Gears are not classified as one of the six simple machines. They are
similar to pulleys in that their motion is usually circular and continuous.
However, gears have an advantage over pulleys. They cannot slip.
Many bicycles have gears to help make pedaling as effortless as
possible. See Figure 8-35. When climbing hills, the cyclist selects a low
gear to make pedaling easier. When descending a hill, the cyclist uses a
higher gear that provides a high speed in return for slower pedaling.
A mechanical clock contains many different sized gear wheels. They
are arranged so that they rotate the clock hands at different speeds.
gure 8-34. Screw threads are used
on vises and C-clamps. They convert
rotary motion to straight-line motion.
gure 8-35. Notice how gears
are used in this bicycle. What is the
advantage of using gears instead
of pulleys?