5
Education
®
1. You used a crude measurement to compare the input and output speeds of the gear
wheels in the experiment you just performed. What you discovered was a simple
Gear Ratio.
2. A more accurate approach is to compare results by counting the number of teeth on
each gear wheel.
For example: 14/84 gives a gear ratio of 1/6 or 1:6
3. A 1:6 gear ratio means that for every complete revolution of the driver gear, the
driven gear makes 6 complete revolutions. Or, said another way: the output speed
is faster than the input speed.
4. (a) Now remove the fan blades from your crank fan and set aside.
(b) First, use the large gear as the driver gear and the small gear is the driven gear.
(c) Second, use the small gear as the driver gear and the large gear is the driven
gear.
NOTE: Do not to
disassemble your fan.
Simply attach the crank to
the appropriate shaft. (See
diagrams below.) In order to
watch the speed of rotation
of the second gear in the
gear chain, you should
attach a yellow connector to
the end of that gear’s axle.
(This connector replaces the
blades that, if used on the
lower axle, will strike the
tabletop unless the model is
pushed to the very edge.)
EXTENSION ACTIVITY: Gear Ratios
Number of teeth on the driven (follower) gear
Number of teeth on the driver gear
Gear Ratio =
Set-up one:
Crank on upper axle. Put the
yellow connector on the end of the lower axle.
Set-up two:
Crank on the lower axle. Put the
yellow connector on the end of the upper axle
where the blades used to be.
