What is the principle of the lever?

The principle of the lever is indeed that it amplifies an input force to lift a load, with the effect dependent on the distances from the fulcrum to where the input force and the load are applied. This is often referred to as the mechanical advantage of the lever, which allows a smaller applied force to lift a larger load when the distance from the fulcrum where the force is applied is greater than that of the load.

In mechanics, the lever operates on the basis of the equilibrium of torques. The formula for the lever states that the torque produced by the input force at one end must equal the torque produced by the load at the other end for the lever to balance. Therefore, if you apply a force farther from the fulcrum than where the load is placed, you can lift heavier loads with less force.

This principle is crucial in various applications, from simple tools like crowbars and seesaws to complex machinery. The effectiveness of a lever comes from both the force applied and the distances involved, making the option that highlights amplification of the input force and the role of distance from the fulcrum the most accurate representation of a lever's principle.