A quick bicycle experiment

If you ask a dozen physicists this question you won't get agreement. So try it, it'll only take a couple of minutes.

1. Turn a bicycle upside down so that it is resting on the handlebars and the saddle.
2. Wind the pedals round by hand and get the back wheel spinning.
3. If the cycle starts bouncing up and down on the saddle springs then try:
   • Spinning faster to break the resonance
   • Let the wheel come naturally to rest. Add a bit of plasticine or putty to the TOP rim. After a couple of goes the wheel should be balanced.
4. Jam on the brakes.
5. Question:
   Are the saddle springs...
   1. Compressed (Bicycle pushes down)
   2. Relaxed (Bicycle tries to take off)
   3. Not affected
   4. Something else happens

The fun of this experiment is that once you know, you can ask a physicist and get an answer along the lines of a dressed-up guess: "I think it should ...". See how much money you can wager on it. Be subtle and hustle!

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