Levers are objects that pry things loose. Levers pivot against a fulcrum. An example of a lever is the end of a hammer that has the claw. When pulling up a nail, the arm rests on a point, and when rotated, the arm pries the nail out. A load is the object moved by the lever; in this case, the nail is the load. Objects are easier to move when located close to the fulcrum. Crowbars and bottle openers are also examples of levers.
When a level plane is slanted, or inclined, it can help move an object across a given distance. Inclined planes help move objects from lower to higher places. One of the most widely used versions of an inclined plane is a ramp.
The wheel and axle is another version of the lever. When an axle turns, the wheel moves, making it easier to move objects from place to place. Obvious examples of wheels and axles are on automobiles. The body of a car rests on the axles; when they move, the whole car moves. Other known devices that use wheels and axles are clocks and doorknobs.
Wheels that move axles can also rotate ropes. A pulley is in the same family as the wheel and axle. Ropes or cords fit over a wheel and are attached to a load at one end. The load moves when the other end of the rope or cord is pulled over the wheel. Pulleys make moving heavy loads an easier task. Pulleys are used in flagpoles, clotheslines and sailboats.
A wedge is an extension of the idea of an inclined plane. The pointed edge of an inclined plane can be used to push, or wedge, things apart. Examples of wedges are axes, nails and knives.
A screw is also another version of the inclined plane. If an inclined plane is wrapped around a cylinder, a screw is formed. Work is done by moving a material up the inclined plane; as this happens, the screw digs deeper into a given material. Screws are used to raise and lower objects as well as hold things together. Spiral staircases, lids on jars and light bulbs all use the screw simple machine in their construction.