How Do Pulleys Work?

Pulleys work by redirecting and increasing the force applied to the load, making it easier to move. Pulleys can either be fixed, mobile, or a combination of the two.

When you increase the distance, like having a longer handle on a screwdriver, you reduce the amount of force needed. Pulleys are a simple machine which increase mechanical advantage. The more pulleys you use, the bigger your advantage. This is why you will see systems of pulleys.

A bulldozer is a good example of a pulley. When you put two or more wheels together, and run a rope around them, you have created a pulley and a great lifting machine. If there are four wheels, you can lift four times as much. If you put two or more pulleys together, you have a block and tackle.

Machines Increase Force

Pulling and pushing actions require force. The more force you can exert, the stronger you are and simple machines allow you to be stronger by helping you use more force.

A machine is anything that increases force. This can be a hammer, whisk, knife, or thumbtack. If there is something you cannot do by hand, then anything that helps you perform that action is a machine.

Simple Machines

In addition to pulleys, there are five other simple machines:

Levers
Wheel and axles
Ramps
Screws
Wedges

In all simple machines, the force you produce is greater than the force you apply.

Levers

Levers include pliers, scissors, see-saws, wheelbarrows, and tongs. Not all of these levers work in the same way, so there are three classifications of levers.

Class 1 levers have force applied on the opposite side of the fulcrum, or pivot point. On a see-saw, the farther away from the fulcrum you sit, the bigger the force you can produce. This is why it is easier to use a tool with a long handle. Scissors and pliers are examples of a class 1 lever.
Class 2 levers have the fulcrum at one end, like wheelbarrows, nail clippers, and nutcrackers.
Class 3 levers also have the fulcrum at the end, but you exert force in the center and the higher force is produced at the tips, as in tweezers and tongs.

Wheels and Axels

Wheels and axles were invented over 5000 years ago and made a huge impact on transportation. It became much easier to push a heavy cart or box. On cars and bicycles, the bigger the wheel the faster you can go with the same amount of force that you apply. Wheelbarrows combine levers and wheels and are extremely useful machines. A clock is another example of a wheel and axle.

Ramps

A ramp is an inclined plane where you lift or lower something slowly at an angle rather than straight up or down. Even though the object travels farther, the effect is the same and less force is used. When walking up a hill, you will sometimes zig zag because that takes less energy even though you walk farther.

Screws

A screw is kind of like a ramp wrapped in a circle. Screw heads work like a wheel or lever, so less force is needed to do the job. The job is also made a little easier by the cone shape of the screw, with the tip being smaller and needing less force as well.

Wedges

Wedges are sometimes not included in a list of simple machines, because they are really two ramps or inclined planes. The head of an axe is a good example as it forces wood apart using a wedge. The handle of the axe is a lever, applying more force to the task. Examples of wedges are knives, the tips of forks, nails, and door stops.

Simple Machines Expand Capabilities

The human body is limited in the amount of force it can exert, so simple machines help it pass beyond that limit. You can make the job easier by adding a simple tool to the task.