A lever is a rigid bar that rests on a fulcrum (a fixed point.) Something or someone must put force (push or pull) on a lever to make it work. The farther the force is from the fulcrum, the easier it is to work the lever. Levers may change the direction as well as the amount of force. There are three classes (kinds) of levers.

A class-1 lever has its fulcrum located somewhere between the effort and the load. The direction of force is changed with this type of lever. Applying effort downward moves the load up and applying effort upward moves the load down. Examples of class-1 levers that you may be familiar with are the playground seesaw, a crowbar, scissors, and pliers.

A claw hammer is a class-1 lever. The handle and the claw of the hammer work as the lever arm. The fulcrum is the top of the hammer head. It rests against the wood. The nail you are trying to pull out of the wood is the load. Although you push the handle for a greater distance than the claw moves, you don't need as much effort to pull the nail from the wood.

With a class-2 lever, the fulcrum is at one end, the effort is at the other end and the load is in the middle. With this kind of lever, the direction of effort is not changed. Pushing up on the lever arm pushes up on the load.

A wheelbarrow is a class-2 lever. Effort is applied to the handles of the wheelbarrow and the wheel is the fulcrum. The load sits close to the fulcrum. Other common examples of class-2 levers are a screwdriver, a catapult, a nutcracker, and a stapler.

Another arrangement of the lever can be found in a class-3 lever. The fulcrum is at one end and the effort is applied between the fulcrum and the load. With this kind of lever, the direction of effort is not changed. The load moves in the same direction as the effort.