How To Calculate Actual Mechanical Advantage

Mechanical advantage is the ratio of force output from a machine divided by the force input into the machine. It therefore measures the machine's force-magnifying effect. Actual mechanical advantage (AMA) can differ from the ideal, or theoretical, mechanical advantage when friction is taken into account. For example, the actual mechanical advantage from a lever will not be significantly less than the theoretical mechanical advantage, because there is no significant mechanism for losing energy through friction. On the other hand, a rope-pulley system may lose a lot of energy through friction in the pulley wheels.

Step 1

Attach a Newton scale (it measures force instead of mass) to the input end of the machine in question. For example, for a pulley system, you'd tie one end of the scale to the pulling end of the tackle, or line.

Step 2

Exert enough force through the scale to hold the load static and then take a reading. For example, you'd pull the tackle of a pulley system out a few inches just to lift the load completely off the ground, and then take a take a force reading off of the scale. This is your Force In.

Step 3

Weigh the load directly with a Newton scale, attaching the load at one end and lifting the load by the hook on the other end of the scale. Take a reading when the load is static. This is your Force Out.

Step 4

Divide Force Out by Force In. This is your actual mechanical advantage.