What is a Compound Machine? - Definition & Examples

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  • 0:01 Compound Machines and Work
  • 0:25 What Are Simple Machines?
  • 1:58 Simple Machines…
  • 3:18 Examples of Compound Machines
  • 4:18 Lesson Summary
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Lesson Transcript
Instructor: Rachel Tustin

Dr. Rachel Tustin has a PhD in Education focusing on Educational Technology, a Masters in English, and a BS in Marine Science. She has taught in K-12 for more than 15 years, and higher education for ten years.

In this lesson, you will learn how to identify simple machines. In addition, you will learn what differentiates a simple machine from a compound machine. Several examples of compound machines will also be discussed.

Compound Machines and Work

At any point in history, humans have endeavored to find ways to make it easier to do work. Not work in the sense of having a job, but the scientific meaning of work. When force is applied to an object, and it moves in the same direction, it is doing work. For example, if a child applies a force to the pedal on a bicycle, and the gears turn the tires in the same direction, the bicycle is doing work.

What are Simple Machines?

Before getting into compound machines, consider what makes something a simple machine.

Simple machines have no (or just a few) moving parts - hence their name. They do not amplify the force you apply. Instead, they simply change the direction of the force. For example, the curved edges along the screw increases the distance the force travels, allowing you to use less force to do the same task. Mechanical advantage, or MA, measures how easy it is to do work. This is the measurement of the force gained by using the simple machine. In a simple machine, the mechanical advantage, or the magnification of the force, is only one. However, because it changes the direction of the force, it makes work feel easier.

The six simple machines are levers, pulleys, wedges, wheels & axles, inclined planes, and screws. For example, a set of stairs or ramps is an inclined plane. The cutting edge of your dinner knife is a wedge. Skateboards work thanks to their two sets of wheels and axles.

Consider some of the work simple machines do. Imagine simply pushing on the top of a screw to try to get it into a piece of wood. Pushing down straight through the screw would be difficult. However, when the screw is turned, the direction of the force changes, and follows along the curved edges so that the screw can go into the wood. Or, think about pushing on one end of a stick while the other is wedged under a rock. Forces applied at one end, and the object moves at the other end of the stick.

Simple Machines Working Together

A compound machine is two or more simple machines working together. Most of the machines in the world are compound machines. Whereas a simple machine does not always increase the mechanical advantage, a compound machine can. With a compound machine, a smaller amount of force can be used to move objects.

This happens because it can multiply the force that is applied, whereas a simple machine usually cannot. This is because the mechanical advantage of a compound machine is the product of all the simple machines working together.

There are a few terms to know in order to calculate mechanical advantage. The measurement used for the weight of an object someone is trying to move is called Newtons (N), and referred to with a capital letter N. The weight of that object is called the load, or sometimes it's called the resistance force. The actual force you apply to the machine is the effort force.

Mechanical advantage = Resistance Force/Effort Force

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