As the moment arm decreases, what happens to mechanical advantage?

• A. It becomes unpredictable
• B. It increases
• C. It stays the same
• D. It decreases

Answer: (B)

The moment arm concept here is about the two lever arms around a pivot: the effort arm (distance from the pivot to where you apply force) and the load arm (distance from the pivot to where the load acts). Mechanical advantage is the ratio of those arms, roughly described as MA = effort arm / load arm.

If the load arm becomes shorter, the denominator shrinks while the effort arm stays the same. That makes the ratio larger, so you get more output force for the same input force. In other words, mechanical advantage increases. Keep in mind that shortening the load arm improves force output but can reduce speed and range of motion at the joint.