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Question:

How is mechanical advantage of wheel and axle found?

My science teacher gave me homework about simple machines. I can not find the formula in my book or online.

Answer:

Normally we think of the axle driving the wheel, so it is actually a mechanical DISadvantage and a speed advantage. You have to know the radius of the applied force on the axle, which often involves a gear or pulley. But if you are told the torque force at the surface of the axle, then you take the ratio of the axle diameter to the wheel diameter - for example, a 2.4 inch axle with 100 pounds of torque at the surface would have a 1:10 disadvantage (or 1/10 advantage) to a 24 inch wheel and would apply 10 pounds of force at the rim of the wheel. If you are given the torque in inch-pounds or foot-pounds then you have to take the two different radii into account to get actual force.
If the advantage is more than one (1), you need less effort.

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