When does a wheel and axle have a mechanical advantage greater than one?

Great question!

mechanical advantage is the factor of which a machine multiplies the force put into it. For example, if a simple machine has a mechanical advantage of 3 it means that it made the work you did 3 times easier or you only had to put in 1/3 the force you would have if you didn’t have the simple machine.

To calculate the mechanical advantage of a wheel and axle you must divide the radius of the wheel by the radius of the axle. Therefore larger wheels means that the speed of the wheels is faster than the speed of the axle and for each rotation the axle makes the wheels are making multiple rotations. A mechanical advantage of 5 means that the wheels are moving 5 times faster than the axle.

F = MA = radius of wheel/radius of axle, this is 1 when the radius of both the wheel and axle are the same, and greater than one when the radius of the axle is less than the radius of the wheel.