Simple Machines

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Slide 1

Our lives are made easier by the use of machines. Machines are energy or force converters. They convert energy of one kind into another, more useful one. The things like cars, dishwashers and sewing machines that we think of as machines today are made up of less complex machines called simple machines. Even back in the days of the Ancient Egyptians, simple machines were used to help labourers move massive blocks of granite. In this presentation we’re going to explore simple machines and their six basic types. We’ll talk about the ways they transform applied forces into forces of more useful size and in more useful directions. In other words, we’ll talk about the ways that simple machines transform energy to make our lives easier.

Slide 2

We’ll start by describing exactly what simple machines are, then look at some examples of simple machines and how they work. We’ll finish off by talking about the advantages of simple machines.

Slide 3

Simple machines are mechanical devices that change the direction of magnitude of a force. This helps us to accomplish our tasks more quickly or easily. They have few or no moving parts. Although they aren’t as complex as modern machines, they still have wide-ranging applications in everyday life. You use simple machines every day. They improve our efficiency by increasing the amount of work done by an applied force. They transform energy from one form to another.

Slide 4

When a force moves an object through a distance, work is done. We define work to be the product of the force applied and the displacement of the object produced by the application of this force. So, the formula for work is given by W = F times d.
Machines reduce the amount of work required to perform a task by either transferring a force from one place to another, changing the direction of the force, increasing the size of the force or increasing the distance or speed over which a force is applied.

Slide 5

We like to think of six different basic simple machines. These are the lever, the wheel and axle, the inclined plane, the wedge, the pulley and the screw. Some of these machines are related to each other, such as the wheel and the pulley. But each has a specific role to play in doing work.

Slide 6

The lever is a very useful simple machine. It is a bar or board that rests on a support called a fulcrum. If you apply a downward force to one end of a lever, it results in the transfer and increase of that force to give a force in an upward direction at the other end of the lever. Depending on the position of the fulcrum, this allows a small force to lift a heavy weight – even a camel or an elephant!

Slide 7

The location of the fulcrum determines the amount of upward force that the lever can produce. If the fulcrum is closer to the object being lifted, then it is easier to lift the object. If the lever is longer, then the object can be lifted higher.

Slide 8

Levers can be classified into three classes, depending on the position of the fulcrum in relation to the load and the effort (or the downward force). If the fulcrum lies between the effort and the load, we have a first class lever. If the situation is as shown in the middle picture (the load lies between the effort and the fulcrum), we have a second class lever. Finally, if the effort is applied between the load and the fulcrum, we have a third class lever. You might think that only the first class lever (and possibly the second) would be useful, but in fact we can find uses for all three classes of levers.

Slide 9

Here are some examples of levers that you might have seen in your house and used in your body! Scissors, hammers and your jaw are all examples of first class levers. Wheelbarrows, nutcrackers and your foot are examples of second class levers. Tweezers, a fishing rod and your forearm are examples of third class levers. Why not have a look around your house and see how many different levers you can find. What types of levers are they? You’ll be surprised how commonly levers appear in everyday objects.

Slide 10

The wheel has always been considered the major invention in the history of mankind. However, it might interest you to know that the Ancient Egyptians actually managed to move the enormous blocks of granite they used to build the pyramids without wheels. But the job would have been easier if they’d used wheels and axles! Indeed, a wheel would not work as well as it does if it didn’t have an axle. The axle is a rod or pole that runs through the centre of the wheel that allows the wheel to turn freely around it. The wheel spins around the axle in a balanced circle to perform the required task. Obviously, we have wheels and axles on cars and bicycles, but many of our modern machines contain gears. Gears are a form of the wheel and axle.

Slide 11

This slide shows some more examples of wheels and axles. The ferris wheel spins around an axle that passes through the centre of the star. The spokes supporting the cars radiate from the axle. A door knob is also another example of a wheel and axle. The handle is a wheel that rotates around an axle that joins the knob to a face plate. Some other examples of wheels and axles are gears (note the axles passing through their centres in the picture). How many wheels and axles can you see on the bicycle? (there are more than 2)

Slide 12

The third basic type of simple machine is the inclined plane. This is nothing more complicated than a ramp. One end of the ramp is higher than the other end. It is likely that the Ancient Egyptians used gangs of workmen to drag huge granite blocks up long sloping ramps. These ramps allow things to go from a low point to a higher point or vice versa much more easily than simply lifting the blocks. It takes the same amount of work, but lest force, to move an object up a ramp than to move it vertically as the distance the object must be moved over is greater. It is, of course, much easier to move an object down, rather than up, a ramp because of gravity.

Slide 13

Inclined planes (or ramps) occur in many different places, even in other simple machines as we shall see later on. They’re used in skateboard parks, wheelchair ramps and boat ramps, and to get heavy equipment into and out of the back of trucks. A modified version of a ramp is also found in stairs, escalators, ladders, slippery dips and walking paths.

Slide 14

We usually use inclined planes to lift a load. Wedges are basically inclined planes put to a different use. Often they are made up of two different inclined planes joined together. We can use wedges to hold things open, or to push things apart. Wedges can also be used to keep things together or to stop things from moving.

Slide 15

Again, we can find wedges all over the place. Some wedges that are used for separating parts of objects (like pieces of wood) are shovels, axes, knives, pick axes, saws, needles, scissors and ice picks. Wedges such as staples, tacks, nails, doorstops and shims (objects used to fill in space) are used to hold things together.

Slide 16

A pulley is a version of the wheel and axle that is combined with a rope or other cord to allow movement of an object up and down or back and forth. The amount of work required to move the object can be reduced by combining two or more pulleys to do the job. Pulleys can also be used to increase the distance from which a force may be applied, and to change the direction of a force. For example, you raise a flag on a flag pole by pulling down on the rope. The pulley at the top of the pole reverses the direction of the force and raises the flag.

Slide 17

There are three main types of pulleys: fixed pulleys, moving pulleys and compound pulleys. Fixed pulleys change the direction of the applied force while moving pulleys reduce the amount of force that must be applied by a factor of one half. However, when lifting objects, they would still require the force to be applied in an upward direction. For many jobs, compound pulleys are the best choice as they combine the advantages of both fixed and movable pulleys. The force required is halved, and you can continue to apply the force in a downward direction when trying to lift an object.

Slide 18

Pulleys have many uses both in the household and in industry. They are used to raise and lower blinds and curtains, and to close and open them. They are also used on sailing ships to raise and lower sails. In industry, they are used at dockyards to raise and lower heavy cargo, and on building sites they can be used on cranes to move construction equipment and other building materials. Finally, lifts use pulleys to move the lift car up and down from floor to floor.

Slide 19

The screw is made out of an inclined plane that is twisted. This allows the movement of a screw from a higher to a lower position in a circle. This means that it will take up less horizontal space to achieve the same upward or downward movement. Screws are often used to pull things together in carpentry, or to push them apart, for example when we use a car jack to raise a car. Some other examples of screws are jar lids, drills, bolts, screw-in light bulbs, bottle caps and ball point pens. Spiral staircases are another example of a screw.

Slide 20

Let’s summarise the things we’ve learned about in this presentation. Simple machines are mechanical devices that have few or no moving parts. They allow us to accomplish tasks more quickly or better. They reduce the required force by changing its magnitude or direction, transferring the force or increasing the speed or distance over which the force is applied. We’ve studied six basic simple machines and their uses. These are the lever, the wheel and axle, the inclined plane, the wedge, the pulley and the screw.