All simple machines help us to do work. They make work easier, and they do it by changing the direction of force. Force is the effort and pushing that we do. Simple machines take that force and redirect it to make it work better.
They also increase the distance. When we increase the distance, we decrease the effort that we need to use to do work. There are four simple machines we will learn about: levers, pulleys, wheels and axles, and inclined planes. Two other simple machines, screws and wedges, are also included in this page, but will not be studied as much in class. A simple machine just has one of these parts. Complex machines are made up of two or more simple machines put together. |
Force, effort, and work. What's the difference?
Force is the strength or power needed to do something. The force I need to push a small, light box is much less than the force I need to push a large, heavy box. The small box gives me less resistance (pushing back), so it is easier to move. The large box has more resistance, and needs more force. If I increase the distance of the work I do, it decreases the force I need to do the job. Force is changeable.
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Effort is the activity of trying hard to do something. It's how hard we have to try. Effort and force go together. Effort is how much we have to try, and force is how much strength and power we need. Effort can be decreased if we increase the distance. It makes the job easier. Effort is changeable.
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Work is the actual job you have to do. I have to get the box to the top of the building. I can carry it straight up, or use simple machines. The job stays the same, so the work stays the same. If I increase the distance, I decrease the effort, but I don't decrease the work. I am doing the same job, but it takes longer. Work is not changeable.
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Levers
Pulleys
Wheels and Axles
Inclined Plane (Ramp)
Screws
Screws are an inclined plane that is wrapped around a pole and goes up and down. Screws are used to dig holes, to hold things together, and lift things. Screws are stronger and have more holding power than nails.
The parts of a screw that stick out are called threads. The strength of a screw depends on how wide and far apart the threads are. The wider and closer together, the stronger the screw, but it is also harder to push it in. If the threads are farther apart and thinner, the screw has less strength, but is also easier to push in. In the picture below, notice the difference between the three screws. Which one do you think is strongest? Weakest?
When screws were first invented, they were mostly used to lift things up or push things down. They could be used to lift water; this is called an Archimedes screw. They could also be used to push apples, grapes, or other fruits to push out the juice. You could walk around the outside, pushing a bar, and the screw would push down on the fruit. Below, on the left is a picture of an Archimedes screw lifting water. On the right is an example of a fruit press.
Today, we mainly use screws in construction, or building. We use them to hold walls together, to build bookshelves, and hold the covers on our computers shut.
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Wedges
Wedges are two inclined planes put together, to make a shape that is wide at one end, and narrow at the other. The force is pushed at the wide end, and the narrow end pushes things apart. This is different from a regular inclined plane, where we use it to help move things higher. Some examples of wedges are knives and shovels.
A short, thick wedge will break things apart faster, but you will have to use more force. A long, narrower wedge will be easier to push in, but will take longer to split something.
Wedges were one of the earliest simple machines people used. We even have it in our bodies: teeth! Our teeth are narrower on one end, and we use them to cut through food as we eat. People also used wedges to make axes, which cut trees and meat off of animals for food.
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Activities with simple machines:
Videos from School Tube (www.schooltube.com)
A video on how simple machines were used in Egypt to build the pyramids:
A video on how simple machines are used in skateboards
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Bill Nye - Simple Machines
Simple Machines song from Bill Nye the Science Guy's video on Simple Machines
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