Gears are used to increase or decrease force, change direction, or change one type of motion to another. They have enabled people to build devices that increased their ability to accomplish many tasks. Gears have a long history. A complex gear-driven device has been found on an ancient sunken ship near a Greek island. Researchers estimate that the device may have been used around 80 B.C. In order for the device to be made, however, people must have developed an understanding of gears long before that.
During the Middle Ages, waterwheels were combined with gears in early mills. This enabled millers to use the power of moving water to turn the millstones. More grain could be ground with less human effort. When gears were combined with the chain and sprocket on bicycles, riders didn’t have to sit right over the wheel in order to turn it. They could sit in the middle of the bike for better balance. Their pedaling efforts were also more efficient.
Most gear mechanisms are toothed wheels attached to an axle. They come in several types and are made from many different materials. Today, engineered materials are often used to make gears so that they are lighter, quieter, and more durable.
Gears usually work in groups. Their relationship is described using a ratio. When one turn from the driver gear causes a driven gear to make one turn, there is no change in output force or speed. The gears are said to have a ratio of 1:1. However, if the gears are of different sizes, there is a change. You can figure out the gear ratio by counting the number of teeth in both gears and inserting the numbers into this formula:
Number of output teeth : Number of input teeth
Transferring force from a larger to a smaller gear increases force but decreases speed. This arrangement might be used to give a tractor its pulling power. Transferring force from a smaller to a larger gear increases speed but decreases force. This arrangement might work for a fast automobile. Can you think of other ways in which gears are used?
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For this WebQuest, your job is to investigate gears. To demonstrate what you have learned, you will answer the questions included here. You will also complete one of the activities described at the end of this WebQuest.
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Read through the following questions. Then research the Internet resources that are provided for you. As you explore the sites, look for answers to the questions. Keep a record of any sites where you find answers by noting the title and URL (Internet address). For example:
(title) Technology Student Association
(URL) www.tsaweb.org
- Name at least three types of gears.
- What are two or more gears working together called?
- Which type of gear has only one continuous tooth?
- What was the purpose of the Antikythera Device found on a sunken ship near a Greek island?
- From what material were most of the earliest gears made?
- The gears in early mills were not precisely made. What problems did this cause?
- What was responsible for the sudden increased use of metal gears in the eighteenth century?
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Visit the Web sites listed here to find information that will enable you to answer the questions. You may use additional sites if you wish. Be sure to keep a record of any sites you use.
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Several activities are described below. Complete one of these activities (your choice) to demonstrate the understandings you’ve gained by going on this WebQuest.
- Make a drawing of your own Rube Goldberg-type invention in which gears play an important role.
- Research and write a report about a different mechanism, such as the cam and follower. Cover its history and important uses.
- Create a poster explaining the gear system in a simple, one-speed bicycle. Label the gears and show with arrows how the force is transmitted.
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