Math of Bicycles: Gearing Up (Grades 710)
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 "Wheel" Figure This Out
 Gearing Up

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The other factor
that influences the bike is the relationship between how one turn of
the pedal effects the turn of the wheel.
1. Look at the tricycle.
Stand the tricycle upside down, with the wheels pointed up so you can
watch what happens. One complete turn of the pedal produces how many
complete turns of the wheel? Why?
2. For the tricycle,
you have a pedal to wheel ratio of 1:1. This means that one complete
revolution of the pedals creates 1 complete revolution of the wheel.
At this point, do not worry about the size of the wheel, just the number
of times it goes around.
3. Now look at a
standard bike. Gently place the bike so the wheels are up in the air.
Start with a pedal at top of its turn and the valve stem on the wheel
at the top of the wheel. Very slowly turn the pedals one complete revolution
and watch how far the wheel turns. Do not keep the wheel spinning or
coast after you have stopped turning the pedals. One turn of the pedal
produced how many turns of the wheel? What is the pedal to wheel ratio
for this bike? Why do you think the ratio is different from that of the
tricycle?
4. Set one of the
bikes with multiple gears upside down. Count the number of teeth in the
largest gear attached to the pedals. Count the number of teeth in the
smallest gear attached to the wheels. How many of the small wheel gears
would it take to have the same number of teeth as the large pedal gear?
5. Now shift the
bike so the chain is on the large pedal gear and the small wheel gear.
In this setting, one turn of the pedals produces how many turns of the
wheel? How does this compare with the comparison of the number of teeth
in each gear? Why? What is the pedal to wheel ratio for this setting?
6. Now count the
teeth on the largest wheel gear. How does it compare with the number
of teeth in the largest pedal gear? Estimate the pedal to wheel ratio
for this setting. Shift the bike so the chain is in this setting, and
test out your estimate.
7. What setting
has the smallest pedal to wheel ratio? Why?
8. What would have
to be true for the pedal to wheel ratio to be the same as that of the
tricycle?
