# Rotational force problem

1. Jun 28, 2009

### aliaze1

Hello everyone,

My brother and I are designing an electric motor for a bicycle (just for fun). Assuming a 200 lb person rides the bike, there is a normal force on each wheel of 100 lbs. We forgot the formulas related to rotational motion and power (watts, horsepower, torque) for this situation (finding the wattage required to turn the wheel at a certain rate carrying a person of that weight). Thanks!

2. Jun 28, 2009

### Andrew Mason

The normal force is not really an issue.

If you want it to duplicate the power output of a human, you will need an electric motor that will have a power output similar to a human. A physically fit human can produce about 200 watts on a sustained basis and much more in a sprint. See: http://en.wikipedia.org/wiki/Human-powered_transport

AM

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