Six Simple Machines

In the last lesson you learned that a machine is a device that helps us do work more easily and effectively.

All machines are constructed from six basic components, and each of these components is actually a simple machine. The six simple machines are:


In this lesson we look at each of these six simple machines.

The Lever

A lever is a machine consisting of a rigid bar that rotates freely around a pivot point called a fulcrum. This bar and fulcrum arrangement can be used to lift a heavy weight (the load force) with a smaller effort force.


The diagram below shows the three classes of levers and some examples. Study these carefully. Are you surprised to learn that your arm is also a lever?

The Inclined Plane

An inclined plane, often called a ramp, is a sloping surface that can be used to raise a load. Using an inclined plane allows you to exert less force, and that makes the job easier for the worker.

Imagine that you have to lift one of those two-wheeled shopping carts up a curb to the sidewalk. This requires a considerable amount of effort, especially if the cart is full. If you were able to use a curb cut, which is a type of ramp or inclined plane, the task of raising the cart would be much easier.

We use inclined planes just about everywhere. for example, some roads in mountainous areas are designed as switchbacks, which are a series of inclined planes that let cars move up the mountain. Lifting loads is easier with an inclined plane.

The Wedge

A wedge is a machine shaped like an inclined plane, but it does work by being pushed into or up against an object. Axes, chisels, and doorstops are all examples of wedges.

Wedges are used to split or separate objects. For example, an axe splits a log by being driven into it with great force. The triangular shape of the wedge helps drive the segments apart.

Wedges also prevent objects from moving on a horizontal surface. The tire chocks you may have seen on a ferry are wedged tightly against the car's tires to prevent the car from rolling.

Wedges work to multiply the effort force. The longer and gentler the slope of the wedge, the less force is needed to push it into an object. An axe can have a thick wedge shape because you expect to drive it into a log with a forceful swing. A knife, which is a long, thin wedge, requires only a little force to slice meat or peel an apple.

The Screw

Screws are common items used in all kinds of furniture and machinery. They are also simple machines. They multiply force to make work easier.

A screw is a long inclined plane that has been wrapped around a rod. A screw does work by being pushed into an object -- sometimes right through one object into another.

The inclined plane on a screw is very long, giving this machine a large mechanical advantage. Because of this, we can sink screws into hard substances like wood and metal with a small effort force.

Bolts, clamps, and vises also make use of this pulling power. A corkscrew can be used to remove a cork from the opening of a bottle. A drill is a screw that moves through material, hollowing out a cylinder the same size as the drill bit.

The Pulley

Pulleys are ingenious wheel-and-cable systems that allow us to lift or move heavy loads by spreading the load force among the various parts of the machine system. Pianos are heavy instruments -- it takes two or three people to lift a Baby Grand. Yet one person can haul a piano up three stories. How? With the aid of pulleys.

There are several types of pulleys as shown below.

A fixed pulley cannot move from its position. This kind of pulley often hangs from a ceiling or other support. It does not reduce the effort force needed to lift a load; it simply changes the direction in which the effort force is acting. When a movable pulley is used, the strands of the cable share the load force and each exerts an equal portion of the effort force needed to lift the load.

The Wheel-and-Axle

The wheel-and-axle is a simple machine made of a small diameter rod or shaft (the axle) that is firmly fixed to a large diameter wheel. The wheel will not rotate unless the axle also rotates. In many wheel-and-axle machines, the wheel and the axle are made from one piece of material. Some examples of wheel-and-axles include a hand drill, a steering wheel, and a doorknob.

Wheel-and-axle machines can increase the effort force or the speed/distance, making a dual-purpose machine.

When you apply force to the larger-diameter wheel of a wheel-and-axle, the force is transferred to the small-diameter axle, which bears the load force. Believe it or not, a screwdriver is an example of this type of wheel-and-axle. We can exert a small force on the large diameter handle, which translates into a large force on the small diameter shaft. The effort force is transferred to the shaft (the axle) and acts on the load force of the screw.

What happens if you apply force to the small-diameter axle? The force is transferred to the large diameter wheel. Moving the axle through a small distance will move the wheel through a large distance. Here, the mechanical advantage is one of speed/distance, not force, because turning the axle requires a lot of force. We use a wheel-and-axle this way when we pedal a bicycle.

Guided Practice Activity 2