Humans use simple machines every day, possibly without even noticing. A car, for example, uses its axles and wheels to make moving easier by redistributing the force caused by its bulk onto more mobile surfaces, and parts of a car are held together by screws or tightened or loosened by a wrench, an applied use of leverage. In short, simple machines change the way force is applied to an object, mostly in beneficial ways — only a poor tool would make things harder. The fundamental simple tools — each which has a long history of human use — are listed below.
An inclined plane is, quite simply, a ramp. One end of the plane is low and the other is high. The downward slant allows you to move heavy or cumbersome objects with the aid of gravity. If you have ever rolled a large box down the ramp of a moving van, you have used an inclined plane.
Wheel and Axle
A wheel is a circular object, and an axle is a long cylinder. When combined, the axle allows the wheel to rotate 360 degrees. Wheels make traveling long distances or moving heavy objects easier. Cars, bicycles, and dollies use the wheel and axle, and the gears that control a watch or clock are merely modified versions of the same machine.
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A lever can be as simple as a long bar of metal. Levers are used to magnify force, making it easier to lift or separate objects. For instance, when you pry open a door with a crowbar, the crowbar is acting as the lever in that situation. Shovels and the part of a hammer that removes nails are both examples of levers at work.
Pulleys are variations on the wheel and axle. A pulley is usually stationary and wrapped with rope or chain. When you pull the rope, the wheel rotates. The more pulleys you have, the less force needs to be exerted to lift an object. Flagpoles, cranes and window blinds all operate with pulleys.
A screw is a modified version of an inclined plane. If the inclined plane is wrapped around a cylindrical object, it becomes a screw. When you turn a screw, the inclined plane is called into effect to separate wood or other materials. Screws are very hard to remove because the plane around their body creates tooth-like roots in the wood.
Wedges are another simple machine that use an inclined plane as their foundation. A wedge is the sharp edge of an inclined plane and can be used for a number of purposes. Wedges are used to hold doors open, separate surfaces and even out structures. Knives, axes, and other sharp objects are also wedges, but their handle makes them a wedge/lever combination.