Identify the simple machine shown: a long rigid bar balanced on a fulcrum with effort on one end and load on the other.

• A. Inclined plane
• B. Pulley
• C. Wheel and axle
• D. Lever

Answer: (D)

Using a lever means using a rigid bar that pivots on a fulcrum to trade force for distance. The bar sits on the pivot, with effort applied at one end and the load at the other. The key idea is the distances from the fulcrum: the longer the effort arm, the smaller the input force you need to lift a given load on the load arm, in an ideal system. The lever also lets the direction of the force change, depending on where you push.

This setup specifically is a first-class lever, where the fulcrum is between the effort and the load. The other options describe different simple machines (an inclined plane, a pulley, and a wheel and axle) that don’t fit the picture of a bar rotating about a pivot with forces on opposite ends.

So the best identification is a lever.