What Are Simple Machines? - Definition, Types & Examples

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  • 0:02 Machines Change Forces
  • 1:30 Work Input Equals Work Output
  • 4:33 Other Simple Machines
  • 7:13 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

If you need to move or lift a heavy object, it would be wise to use a simple machine. Though these devices are far from fancy or high-tech, they are extremely helpful for getting work done.

Machines Change Forces

Last weekend, I received a really large package in the mail. It was quite heavy, and I could have tried to pick it up myself, but I didn't really like the idea of potentially hurting my back doing this. So, I called a few friends to help, but no one was available, so I was still out of luck. My third option was to use a simple machine, a non-powered device that either multiplies or changes the direction of a force.

You might be wondering what the heck multiplying or changing the direction of a force has to do with moving that package into my house. Well, according to Sir Isaac Newton, in order to move a stationary object, we need to apply a force to it. And when that force is applied over a given distance, we do work on that object. More simply, we can define work as force x distance. So, in order to get that box into my house, I had to apply a force and move it from outside to inside - I had to do some work!

And this is where simple machines come in. Multiplying the force or changing its direction helps us do work. It's important to remember that the law of conservation of energy still applies here - less work isn't actually being done, even though it may feel like it. No machine can create energy - it just transfers or transforms it. The work input will always equal the work output.

Work Input = Work Output

Let's see how this works with one of the simplest machines around - the lever. A lever is a beam that rotates on a support point. This lever support point is called a fulcrum. Ever been on a seesaw at the park? That's a lever! Scissors are also levers, as is the flush handle mechanism in your toilet tank.

If you want to lift something on a lever, you put the object on one end of the beam and push down on the other. You do work on your end because you apply a force, which is exerted through the distance of the beam to the fulcrum.

But work is also done on the other end of the beam as the object is lifted up from the other side of the fulcrum. And what's key here is that the work done on both ends is the same. The product of force and distance on both ends is equal. But this doesn't mean that the forces or the distances are equal on both sides. In fact, making them different is the key to effectively using a simple machine!

Say, for example, that your fulcrum, or support point, is under the middle of your lever beam. The distance on both sides of the fulcrum is the same, which means that the force will be the same on both sides. You will need to apply the same amount of force on your end as it will take to lift the object on the other end.

But if you move your fulcrum so that it's closer to the object you want to lift, you have increased the distance your force is applied over. This means that while the products of the two sides are still equal, the individual components are not. Since the distance you apply your force over is greater, the force you need to apply must decrease to compensate. On the other end of the beam, the distance has decreased, which means the output force must increase to compensate.

Here, the same amount of work is done as before when our fulcrum was in the middle, and the same amount of work is done on both ends of the lever. But simply moving the fulcrum toward the object you want to lift changes the amount of force involved in that work - on both ends.

For the same reason it would not be wise to move the fulcrum toward you and away from the object you want to lift, when the fulcrum is closer to you, the distance your force is applied over is lessened, meaning you need to apply more force. But on the other end, the distance from the fulcrum has increased, meaning there's a decrease in output force to compensate. You've just made it harder to lift the object instead of easier!

It's all about that relationship between force and distance. In all three situations, the work you did was the same. But the difficulty of that work changed depending on how you utilized the relationship of the work components - the force and the distance.

Other Simple Machines

Levers are wonderful, but they certainly aren't the only type of simple machine. Nor are they always the best simple machine to use. It all depends on the work you want to do.

A wheel and axle is a simple machine where two components rotate together to transfer force from one to the other. Think of your car or bike wheels or even a round doorknob, and you'll get the idea of this machine.

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