# Simple Machines

## Introduction to six different devices that make work easier by changing a force.

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Building Coral Castle

### Building Coral Castle

Credit: Keith Yahl
Source: http://www.flickr.com/photos/yahl/4327056748/

You probably recognize these massive structures as Egyptian pyramids. You can tell how big they are by comparing them with the tiny human figures at the left side of the photo. The pyramids have long been recognized as amazing feats of engineering. One of them, the pyramid of Giza, was one of the “seven wonders of the ancient world.” Most of the pyramids of Egypt were built at least 4,000 years ago, when the only tools were simple tools that depended on human or animal power. How were the ancient Egyptians able to perform such marvels of construction?

#### Amazing But True!

• You can get an inkling of the way the Egyptians built the pyramids with the video below. It’s about Coral Castle, a structure in Florida that was built completely of huge chunks of coral.
• Credit: Milan Boers
Source: http://www.flickr.com/photos/milanboers/3507464026/

The courtyard of Coral Castle in Homestead, Florida [Figure2]

• What’s amazing about Coral Castle is that it was built by a single, very small man using only simple machines! How did he do it? Watch the video to find out. You’ll see two teens explore Coral Castle and then use simple machines to try to move a boulder. http://pbskids.org/dragonflytv/show/coralcastle.html

#### What do you think?

Use the interactive activity at the link below to learn more about each of the simple machines the boys in the video used. Then answer the following questions.

1. How much does all the coral at Coral Castle weigh?
2. The two boys in the video first tried to move a boulder over the ground. What type of simple tool did they use? Describe this tool and how it made their work easier. Were they able to move the boulder?
3. The two boys next tried to raise the boulder off the ground. What type of simple tool did they use? Describe this tool and how it made their work easier.
4. The boys’ first attempt to lift the boulder off the ground was a failure, so the boys decided to estimate its weight. How did they make their estimate? How much did they estimate the boulder to weigh?
5. The boys added a winch in their second attempt to lift the boulder off the ground. Which simple tools made up their winch? How did the winch help them lift the boulder?
6. After seeing how simple tools can be used to move a boulder, do you have a better idea of how the pyramids might have been built? What do you think?

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