Inclined planes, wedges and screws

Inclined planes, wedges and screws are related types of force multipliers. They all reduce the force necessary to move an object by increasing the distance the object is transported.

Inclined planes

An inclined plane, commonly referred to as a ramp, is an even surface that is tilted at an angle. It helps reduce the force necessary to move an object by increasing the distance it must be moved. Picture a vertical wall two metres (m) tall. You would have to apply a lot of force to lift a 10 kilogram (kg) object over the wall. Now picture a 5 m ramp leading up to the top of the wall. It would be far easier to move the 10 kg object up the ramp than it would be to lift the object straight up. Ramps are used this way in many applications. They allow people with physical disabilities to move up to another floor in a building, for example, and they help to move objects into a truck.

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Inclined planes work because energy is always conserved. Since work is equal to force times distance, if the distance the object travels is increased, the force necessary to move it decreases. The same amount of work is being done in both cases, but the force necessary to do that work decreases when using a ramp.

Inclined planes have been used for thousands of years by human beings. The Egyptian pyramids, for example, are believed to have been built using inclined planes. When large, heavy slabs of rock had to be moved up the side of a pyramid, it is believed that the Egyptians used ramps to help move the rocks to a higher level.

Inclined planes are also used in road building. On roads travelling down the sides of steep mountains, for example, roads tend to wind up the mountain instead of going straight up. These are called hairpin turns. This way, cars do not have to exert as much force to move up the mountain.

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Wedges

Wedges are a type of inclined plane. Instead of being stationary and having work done upon it, however, the wedge is an inclined plane that is moved through something else. As a wedge is forced into a space in an object, it exerts force to widen the space.

An example of a wedge is an axe. Axes are used to split logs. As the axe is forced into a space in the wood, it pushes the two parts of the log apart. Many other types of cutting implements are also wedges, including knives, scissors, and teeth.

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Another example of a wedge is a nail. As the nail is pounded into a piece of wood, the bottom part of the nail opens up a large enough hole for the shaft of the nail to move through.

Screws

Screws are inclined planes that travel in a circle around a central point. Screws reduce the force necessary to move an object through another object or substance by extending the distance necessary to move the object. In addition, the motion is rotational, which means it spins around a central point.

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An example of a screw is a woodscrew. Woodscrews are used to fasten pieces of wood together. A woodscrew is an inclined plane wrapped around a central shaft. To demonstrate the power of a screw, try to use a hammer to pound a woodscrew into a piece of wood. The wood will resist the screw, and it would take a lot of force to push the screw into the wood. If you turn the screw with a screwdriver, however, it will be a lot easier to push the screw into the wood. Screws like this are used in many applications. A wrench, for example, uses a screw to adjust its size. Screws are also used in water taps. When you turn the tap, it pulls a screw up, allowing water through the faucet.

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Another type of screw is a propeller. These screws consist of multiple inclined planes around a central point. Propellers are used to move objects like aeroplanes, submarines and boats through air or water.

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