In a lever system, which location describes a third-class lever where the effort is applied?

• A. Between the fulcrum and the load
• B. On the same side of the fulcrum as the load
• C. On the opposite side of the load from the fulcrum
• D. At the fulcrum

Answer: (A)

In a lever system, the class is defined by the order of the three elements—fulcrum, load, and where you apply the effort. A third-class lever has the effort applied between the fulcrum and the load. This arrangement lets you move the load quickly and through a larger range of motion, though it requires a greater effort (mechanical disadvantage). A familiar example is a bicep curl: the elbow is the fulcrum, the hand with the weight is the load, and the muscle applies force somewhere between the elbow and the hand. If the effort were on the opposite side of the fulcrum from the load, you’d have a first-class lever (fulcrum between effort and load). If the load were between the fulcrum and the effort, that would be a second-class lever (load between fulcrum and effort). If you apply effort right at the fulcrum, there’s little to no movement.