Pulleys

Hello, I am an orthopaedic resident in Colombia SA, my question is rather simple but I haven´t found the answer. Does the radius or diameter of a pulley affect in any way the work it does? Does a smaller pulley work more that a bigger pulley? What is the relationship between the raduis or diameter of a pulley with the work it does? Thanks
- juancho (age 30)
bogota, colombia

In the standard approximation, where we don’t worry about ay energy required to get the wheel turning, the radius doesn’t matter. The key property of pulleys is that one end of the rope moves more or less than some other point. That allows you to either amplify the motion or amplify the force- like with levers. The wheel radius may be picked to be convenient for whatever rope or cable is being used. Something too small would lead to problems if the rope couldn’t bend sharply enough, or if there were a lot of internal friction in the rope when it bent sharply.

Mike W.

(published on 10/22/2007)