I have to make a compound machine that has an input force of 2N and an output force of 8N-10N. So far this is what I've got. Its a wheel and axle connected to a block and tackle. img130.imageshack.us/img130/4974/physicsbo6.png[/URL] How much bigger will I have to make the wheel than the axle in order to get an output force at least 4x bigger? If it was a frictionless environment the wheel would have to be 2x bigger than the axle or more right? How much should I compensate for friction? I am using metal pulleys I bought that have bearings(or w/e they are called) in them but they do seem to have some friction. I can only get them to make about 3-4 revolutions before they stop.