What defines a first-class lever?

A first-class lever is defined by the arrangement of the fulcrum, load, and effort. In this type of lever, the fulcrum is positioned in the middle, with the load on one end and the effort applied at the opposite end. This configuration allows the lever to change the direction of the effort applied, which can facilitate the lifting or moving of heavy loads with less force.

When the effort is applied at one end, it can create a mechanical advantage, allowing a smaller input force to lift a larger load. Common examples of first-class levers include seesaws and crowbars, where the fulcrum allows for efficient movement and balance.

The other options do not accurately represent the characteristics of a first-class lever. They suggest different arrangements where either the effort and load are placed in a way that does not conform to the definition of this type of lever.