Bicycles
Bicycle cranks have dead centres at approximately 12 o'clock and 6 o'clock where simple pushing down of the pedal will not turn the chainwheel, but the rider's leg is able to apply tangential force at the pedal to overcome it. Fixed-gear bicycles (without a freehub) use the momentum of the bicycle and rider to keep the chainwheel turning even if the rider makes no attempt to pedal in a circular motion.
Read more about this topic: Dead Centre
Famous quotes containing the word bicycles:
“Holland is a dream, Monsieur, a dream of gold and smoke—smokier by day, more gilded by night. And night and day that dream is peopled with Lohengrins like these, dreamily riding their black bicycles with high handle-bars, funereal swans constantly drifting throughout the whole country, around the seas, along the canals.”
—Albert Camus (1913–1960)