Final answer:
A lever is a simple machine consisting of a rigid bar pivoted at a fixed point called the fulcrum. There are three different classes of levers: first-class levers, second-class levers, and third-class levers.
Step-by-step explanation:
A lever is a simple machine consisting of a rigid bar pivoted at a fixed point called the fulcrum. There are three different classes of levers: first-class levers, second-class levers, and third-class levers.
In a first-class lever, the fulcrum is located between the input force and the output force. See figure 1 in the reference materials. Examples of first-class levers include a seesaw and a pair of pliers.
In a second-class lever, the fulcrum is still located at one end of the lever, but the output force is between the fulcrum and the input force. An example of a second-class lever is a wheelbarrow.
In a third-class lever, the input force is applied between the fulcrum and the output force. Examples of third-class levers include a broom and tweezers.