Simple Machines

And how they work

What's a Machine?

A machine is something that makes work easier (in most cases ). What it does is it lowers the size or changes the direction of the force you apply.

How this works is by decreasing the input force ( the force that you put into the machine) , and increasing the output force ( the force that the machine applies to do the task), in most cases.

Simple Machines


A lever has a bar that rotates at a fixed point, which is called a fulcrum. The force applied to the lever is called the input force. The object the lever is working on is called the load. What the lever does is apply force to the load. There are three classes of lever, all of which have different locations for the fulcrum, the load, and the input force on the bar.

Types Of Levers

In first class lever, they have the fulcrum in between the input force and the load, as shown in the figure below.

In second class levers, the load is between the fulcrum and the input force, as demonstrated in the diagram below.

Lastly, third class levers, the input force is between the fulcrum and the load, as shown below.

Force -Distance Trade Off

What the lever does is make work easier (in most cases). It does this by decreasing the force you apply to the lever, by increasing the distance at which the force is applied.

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A pulley is a simple machine with a grooved wheel that holds a rope or a cable. Once again, the object being lifted is the load, and the input force is applied to one end of the cable. The load is attached to the other end of the rope or cable.

Fixed Pulleys

A fixed pulley is connected to something that doesn't move, hence the word fixed ( as in fixed position). To use a fixed pulley, you pull down the rope to lift the load. The direction of the force changes. Since the size of the output force is the same as the input force, the mechanical advantage (MA) is 1.

Movable Pulleys

These types of pulleys are connected directly to the object that is being moved, which is the load. The direction does not change, but the size of the force does. The mechanical advantage (MA) of this pulley is 2. This means less force is needed to move a heavier load.

Block and Tackles

If you combine a fixed pulley and a movable pulley, you form a pulley system, know as a block and tackle. The mechanical advantage (MA) of this simple machine is equal to the number of sections of rope in the system.

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Wheel and Axle

The wheel and axle is basically what its called, a wheel and an axle. It is a simple machine that is made up of a wheel and axle that move together, the wheel being the larger object and the smaller object being the axle.
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Inclined Plane

An inclined Plane is a simple machine that has a flat, slanted surface. An example of an inclined pane is a ramp. When using an inclined plane, the input force is smaller that the objects weight. The same amount of work is done, but it happens over a longer distance.

If the length of the inclined plane is much greater than the height, the mechanical advantage is large. This means that an inclined plane with a gradual slope needs less force to move objects than a steep sloped one.

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A wedge is made of two inclined planes that move.Similar to an inclined plane, a wedge needs a small input force over a large distance The output force of the wedge is much greater than the input force.

A wedge has a greater mechanical advantage if it is long and thin. This means there is a smaller input force over a longer distance.

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A screw is basically an inclined plane that is wrapped around a cylinder. In order to turn a screw, a smaller force over a long distance is needed. The screw applies a large output force over a short distance.

To find the mechanical advantage of A screw, you have to find the length and the width of the inclined plane that is wrapped around the cylinder. ( This is just calculating the
MA of an inclined plane). The longer the spiral on a screw and the closer the threads, the greater the screw's mechanical advantage.

Compound Machines

Most machines used are known as compound machines, which are made of more than 1 simple machines. A real life example of a compound machine is an ax. The handle is the lever, and the top part of the ax is a wedge, which is made up of 2 inclined planes.

Mechanical Efficiency

Most compound machines have a very low mechanical efficiency ( measures the ratio of work output to work input in a machine).Because there are various parts moving in a compound machine, the efficiency is low due to the fact that more parts are moving and are making contact with each other. This means more friction, which lowers the output force.

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