Pedals on a Bicycle
Balance an ordinary bicycle upright without restraining its motion in any way.
Position the pedals so that they are top-and-bottom. Standing on the ground
alongside the bike without mounting it, grasp the top pedal and push it
forwards (in the normal direction of travel). The pedal moves forward and
so does the bike of course.
Now, reposition the pedals as before, but this time grasp the lower
pedal and push backwards.
(Try to solve this puzzle in your head before referring to an actual bicycle.)
- Which way does the bike move?
- Which way does the pedal move?
Source: Reader Peter Bentley, citing someone named "Jellio".
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