Simple machines

The word machine often conjures up an image of a big, complicated device powered by electricity. Machines actually come in all shapes and sizes. The very essence of a machine is to make life easier; the word’s origin is both Greek and Roman, meaning “makes work easy” and “trick.”

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Spoked wooden wheel with iron rim.Heritage Transport Museum

Used for thousands of years, Archimedes first described simple machines 2,000 years ago. A total of 6 simple machines have been recognized: inclined planes, wedges, levers, pulleys, screws, and the wheel and axle. 

Wheel and Axle

All simple machines work by changing a force, either by transferring it, magnifying it, or changing its direction. Simple machines are often used as building blocks to produce more complicated machines. 

For example, you can find 3 simple machines within a bicycle: levers, pulleys, and the wheel and axle.

Development

Prior to the wheel, large items were placed on log rollers. As the object was moved forward logs were taken from the back and moved to the front. Another method of transportation was to have animals drag heavy objects along the ground.

History

Around 5,000 years ago, a wheel was placed on an axle and changed the world. The technology first appeared in Poland and was independently invented by the Chinese soon after. 

Physics

A wheel attaches to a straight rod called an axle. These 2 parts rotate together to reduce friction between the wheel and the ground. Friction that occurs at the point where the wheel and axle meet can be decreased by the addition of bearings.

Significance

Considered to be one of the most significant inventions in the history of humanity, the wheel and axle allowed humans to move large objects over great distances. It accelerated the spread of trade as goods were transported with ease to faraway markets. 

Force

As with all simple machines, the wheel and axle combination multiplies force. This means it takes very little effort to create a large amount of force. And the bigger the wheel, the easier it is to push as it works like a big lever.

Levers

To achieve the needed multiplication of force, simple machines apply force over a much longer distance or period of time. Inclined planes, screws, and levers increase the distance over which a reduced force acts, allowing us to push or pull with smaller effort. 

History

The invention of the lever is lost in time. Humanity has probably been using levers since our common ape ancestors. Many animals like apes, otters, and crows also use levers. 

The Device

A lever is a long, straight rod that is balanced on a fulcrum, or pivot, that does not move. The fulcrum can be placed at various points along the lever in order to produce different effects. 

First Class Lever

There are 3 different types of levers. A first class lever has the fulcrum in the middle of the rod and the load placed at 1 end. Resistance applied on 1 end of the lever lifts the load at the other end. 

Second Class Lever

A second class lever’s fulcrum sits at 1 end of the lever. Resistance is then placed at the other end and the load is in the middle. The wheelbarrow is an example of a second class lever.

Third Class Lever

A third class lever has the fulcrum at 1 end of the lever, resistance is placed in the middle, and the load is at the other end. Many of the musculoskeletal systems in the human body are third class levers.

Wedge

Simple machines are useful because they allow us to perform tasks beyond our physical capability. Some simple tools have been used by humans (and animals) for around 200,000 years. 

Many monuments built thousands of years ago were built using simple machines such as inclined planes, pulleys, and wedges. 

History

The wedge has been used by humans for around 200,000 years. Rocks were sharpened into the shape of a wedge and then used as axes or to scrape animal skins. 

The Device

A wedge is a tool with at least 1 inclined edge. Both of its edges work together to increase force, in order to either separate something or hold something together. 

Forces

A wedge like an axe is used to change the direction of force. A downwards force is applied but the resulting force splits into 2 sideway forces, breaking wood apart. 

Inclined Plane

Simple machines (with the exception of the wheel and axle) only need 1 part in order to work. Although simple machines were described some 2,000 years ago it wasn’t until the Renaissance in the 17th century that the physics behind these machines were studied.

Galileo was the first scientist to describe the mathematical similarity of the machines in 1600.

History

The inclined plane, also called a ramp, was not considered a machine until the Renaissance. This is mainly because inclined planes have no parts that move in order to change force. 

The Device

 An inclined plane is basically a sloping surface. Inclined planes are commonly used to either move objects from a lower point to a higher point or the other way around. 

Forces

Objects increase force when they are rolled down an inclined plane. This rate can be changed based on the angle of the inclined plane. Moving an object up an inclined plane takes less force than lifting the same object straight up. 

Cost

The cost of moving an object to a higher area using an inclined plane is the distance needed to move the object. The steeper the angle, the more force is needed. To make the work easier, some inclined planes need to be quite long.

Screw

Simple machines reduce friction, they do not eliminate it entirely. There is always some power lost to heat. Some simple machines can be used in either direction, such as levers, but others can be self–locking.

Self–locking means that it is extremely difficult to get the machine to work in the other direction. An excellent example of a self–locking simple machine is a screw. Once the screw is in place it is almost impossible to pull it out. 

History

Believed to have originated in either ancient Greece or ancient Egypt, the screw helped lift water to use in irrigation and possibly remove bilge water from ships. Ancient Greeks and Romans used screws to extract oil from olives and juice from grapes.

The Device

A screw is an inclined plane wrapped around a cylinder. Screws are used to hold things together, make holes, and move air and water (in the case of propellers) as well as help lift heavy objects. 

Forces

A screw converts rotational force (spinning) to linear force (moving up or down). As with all simple machines, little resistance (turning the screw) is needed in order to magnify the force. 

Inclined Plane

Adding more thread makes a screw easier to turn, but it takes longer to achieve the desired result. Like a longer inclined plane, it will be easier to push the load up, but it needs a greater distance.

Pulley

Even though each simple machine works differently mechanically, mathematically they work in a similar manner. In every machine a force (Fin) is applied and a load is moved (Fout). 

As simple machines do not contain energy themselves, the output of force can only be changed by the input. 

History

The pulley’s origins are relatively unknown. Evidence exists of pulley use in Mesopotamia from 3,500 years ago, used to hoist water. Archimedes may have used a block pulley to pull a warship filled with people over 2,000 years ago.

The Device

A pulley is made up of a grooved wheel which turns inside a frame, or block. A rope runs through the block and over the wheel’s groove. Similar to a wheel and axle, the rope acts like an axle, being rotated by the wheel.

Forces

When 1 end of the rope is pulled, the load at the other end is raised. A pulley only changes the direction of the force applied. Adding more wheels decreases the force needed to lift heavy objects, but increases the length of rope needed. 

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