According to Ohio University, there are three main classes of levers. These are distinguished by the relative locations of the load, effort and fulcrum along the lever. A second-class lever is one in which the load, or the item being lifted, is found between the effort and the fulcrum, or pivot point.
First-class levers are those which have the fulcrum placed between the load and the effort. Examples of first-class levers are the seesaw and crowbar. On a seesaw, for example, the person on the higher end of the plank acts as the effort, applying a downward force to the end of the lever. The person on the other end is the load, and the point at which the plank pivots is the fulcrum.
Ohio University lists the wheelbarrow as an example of a second-class lever. The effort is applied to the handles, the axle of the wheel acts as the fulcrum or pivot point, and the load is found in the middle.
Third-class levers are those in which the load and fulcrum are located at opposite ends of the lever with the load placed between them. An example of this class of lever is the hammer. When used to pound a nail into a board, the user's wrist is the fulcrum, the point at which the hand contacts the hammer is the effort, and the resistance of the wood to pounding is the load.