# Understanding the Efficiency of Compound Machines

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• 0:01 Compound Machines
• 1:12 Examples
• 2:22 Efficiency
• 4:20 Lesson Summary

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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Compound machines are made up of two or more simple machines. When you combine simple machines, you increase the mechanical advantage, but might have to sacrifice some efficiency. Learn about compound machines and see examples.

## Compound Machines

Every spring I spend a lot of time getting my garden ready for the growing season. It's a lot of hard work. One item that I rely on to make my work a bit easier is my wheelbarrow. Now, when you look at a wheelbarrow, you probably think of it as a pretty simple piece of gardening equipment. After all, it's nothing more than one wheel, a large bucket and a couple of handles. However, as far as science is concerned, a wheelbarrow is a compound machine. It qualifies as a compound machine because it's a machine that consists of two or more simple machines.

You might recall that simple machines are things like levers, pulleys, wheels with axles, screws, wedges, and inclined planes. A wheelbarrow consists of two simple machines. The wheel and axle is one simple machine, and the long handles that are supported by the fulcrum over the wheel make a second simple machine called a lever. In this lesson, we will look at some additional examples of compound machines and describe their efficiency as well as their mechanical advantage.

## Examples

The truth is that compound machines are all around you, and you use them to make tasks easier. For example, when I want to prune the shrubs around my yard, I use gardening shears, which look like a huge pair of scissors. Gardening shears, like scissors, are an example of a compound machine. When we look at the shears, we see two types of simple machines. The bars of the shears crisscross at the center, which acts as the fulcrum of the levers. The blades of the shears are a different type of simple machine known as wedges. Wedges are considered simple machines because they help to push things apart.

Some compound machines consist of hundreds, or even thousands, of simple machines. The lawnmower that I use to cut grass is an example of a compound machine that is made up of multiple simple machines. For example, the spinning blade underneath the mower is a wedge. The wheels and axles help you push the mower through the yard. The long handles pivoting on the back wheels create a lever, and even the gas cap is an example of a simple machine, called a screw.

## Efficiency

Compound machines can help you get your work done, but because they contain more moving parts than simple machines, they lose some efficiency. Efficiency is defined as the ability to do work with the least waste of energy.

Compound machines lose efficiency due to the increased friction caused by all of the moving parts. Friction is the resistance that is created when one object tries to move over another object. In highly complex compound machines, like your car, friction can become quite intense, resulting in heat that could damage your engine. To reduce friction in your car and similar machines you use lubricants, like oil and grease. These lubricants help reduce friction and keep heat, as well as wear and tear, to a minimum.

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