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Project Summary

Difficulty	4
Time required	Very Short (a day or less)
Prerequisites	None
Material Availability	Readily available
Cost	Low ($20 - $50)
Safety	No issues

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Sponsored by a generous grant from Seagate

Abstract

Objective

In this experiment you will count the number of teeth on gears and figure out how to calculate gear ratios by putting the gears together.

Introduction

What exactly do gears do? They crank, mesh, pump, push, pull, tug, and grind. All of which turn out to be very useful for doing work. Many mechanical contraptions and gizmos use them, but how do they do work? The LEGO Education Connection explains:

Moving gears (Public Domain).

"A gear is a wheel with teeth on its outer edge. Gears rotate on a central axis and work with other gears to transmit turning force. The teeth of one gear mesh with — or engage — the teeth of another gear.

"The rotating force produced by an engine, windmill, or other device often needs to be transferred or changed in order to do something useful. For example, as you pedal a bicycle, you cause the sprocket to rotate. But in order to make the bike move, this rotating energy must be transmitted to the rear wheel.

"Gears are used to transmit turning force. They can also change the amount of force, speed, and direction of rotation." (LEGO, 2007)

Gears are generally used for one of four different reasons (Brain, 2000):

• To reverse the direction of rotation
• To increase or decrease the speed of rotation
• To move rotational motion to a different axis
• To keep the rotation of two axes synchronized

All of this, of course, depends on how the gears fit together. The most important thing to consider when putting two gears together is the gear ratio. This is a way of expressing the size of one gear relative to another. For example, LEGO makes gears in the following sizes: 40-tooth, 24-tooth, 16-tooth, and 8-tooth. An example of how to figure gear ratios follows (Genalo, 2000):

Line the first set of gears in front of you. Make a ratio of the number of teeth in the first gear against the number of teeth in the second gear. For example, if you have a 24-tooth gear and an 8-tooth gear: 24:8 = 3:1 The ratio would be 24:8. Find the greatest common denominator of this ratio and use it to simplify the ratio. The simplified ratio would be 3:1.

In this experiment you will use a set of toy gears to figure out an alternate way to determine the gear ratio. You will also try to figure out how the gear ratio will affect the revolutions per minute of two gears that are meshed together. After figuring this out your inventions will only need a dab of imagination!

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• gear ratio
• driver
• follower
• gear up
• gear down

• How do gears work?
• What does a gear ratio tell you?
• How can gears be used for making things work?

Bibliography

• A very nice site explaining how gears work from LEGO Education:
  LEGO, 2007. "Connections: Gears," LEGO Education: LEGO Group. [accessed February 3, 2007]
  http://www.legoeducation.com/content/item.aspx?CategoryID=100&art=3
• This site describes gears in more general terms and has a nice animation of two gears turning:
  Brain, Marshall, 2000. "How Gear Ratios Work ," HowStuffWorks.com [accessed February 2, 2007]
  http://www.howstuffworks.com/gears.htm
• Genalo, L., 2000. "Challenge Corner," Toying With Technology News, Iowa State University, volume 2, issue 1. [accessed February 3, 2007] http://www.eng.iastate.edu/twt/Pixandnews/newsletters/news/newsf00.pdf

Materials and Equipment

• a set of toy gears that fit together and come in a variety of sizes; Here are a few good ones that are available at national retailers like Amazon, Toys-R-Us, or Target:
  • LEGO gear and building sets (best)
  • Gears!Gears!Gears!® Gizmos by Learning Resources
  • Kaleidogears by Quercetti Georello
  • Gearation by Tomy
• different colored stickers or tape
• black permanent marker
• partner to help count

Experimental Procedure

1. For this experiment you will need a data table to write all of your numbers:

   	Smallest <============> Largest
   Gear:	A	B	C	D	E	F
   Teeth of the Gear
   Teeth of Gear A
   Ratio of Teeth
   Turns of the Gear
   Turns of Gear A
   Ratio of Turns

2. Sort through your gear set to find a series of gears in different sizes that all fit together.
3. Put the gears out on the table in order from smallest to largest.
4. Place a small sticker or piece of colored tape next to ONE tooth of each gear, choosing a different color for each gear to help you keep track. Label each sticker with a letter (A, B, C, D, etc.) that you will use to identify that particular gear in your data table.
5. Using a permanent black marker, color that SAME TOOTH black so that it stands out and is easy to see. Don't worry about the marker being permanent, you can wipe it off later with some rubbing alcohol.
6. Count the number of teeth on each gear and write the numbers in your data table.
7. To calculate a ratio, divide the number of teeth for each gear (found in the 1st data row of your table) by the number of teeth on Gear A (found in the second data row of your table). Write your answer in your data table (in the 3rd data row of this table).
8. Check your math. Your ratio for Gear A should be 1:1, or 1.0 if you are using a calculator. If it is not be sure to check your math to be sure you are doing it right.
9. Starting with the smallest gear (A), attach it to the next larger gear in size (B) using the connectors in your toy gear kit.
10. Rotate until the two teeth marked with black permanent marker are directly next to each other. This will be your starting point.
11. Now rotate the smallest gear slowly in one direction until the two marked teeth touch together at exactly the same point as before. Count the number of rotations of both gears as you go from start to finish. There may be a lot of turns to count! You can either find a volunteer to count the other gear for you (best way) OR you can complete this step twice, counting one of the gears each time from start to finish (most tedious way). Write the number of turns that each gear makes into your data table.
12. Repeat this step with each of the larger gears (D, E, etc.) connected to the smallest gear (A) counting the number of revolutions for both gears each time.
13. Again, calculate a ratio by dividing the number of turns of each gear (found in the 4th data row of your table) by the number of turns of Gear A (found in the 5th data row of your table). Write the answers in your data table (for example, the last row of this sample data table).
14. Compare your two ratios. Are they similar or different? What does this tell you about how revolutions per minute are related to gear ratios?

Variations

• In this experiment you used the number of turns to calculate a gear ratio, by simplifying a fraction. Can you use the number of teeth in the two gears to get another fraction that will simplify the same way? Will this also calculate the gear ratio?
• In this experiment you tested the smallest gear against each of the larger gears. A more advanced project is to test all possible combinations of gears. Here is one way to make a table to help you figure out what all of the possible combinations are:

  	A	B	C	D	E
  A	AA	AB	AC	AD	AE
  B	-	BB	BC	BD	BE
  C	-	-	CC	CD	CE
  D	-	-	-	DD	DE
  E	-	-	-	-	EE

• Attention gear-heads! If you like gears and bikes, then this might be of interest to you. You can count the number of teeth on each gear of your bike and see if it relates to the rpm of your wheels. Just prop up your bike and crank the pedals with your hand at a constant speed. Then have someone help you count the number of turns the wheels make in a minute to get the rpm's. Check out a short description in the Additional Projects section on the Applied Mechanics interest area page.
• More advanced students can order specialized gears and calculate more complex gear ratios. You can also calculate how gearing up or gearing down will change the revolutions per minute. How is this useful for applied mechanics?

• For more science project ideas in this area of science, see Mechanical Engineering Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2007-04-03 22:00:00

Career Focus

If you like this project, you might enjoy exploring careers in Mechanical Engineering.

Mechanical Engineer Mechanical engineers are part of your everyday life, designing the spoon you used to eat your breakfast, your breakfast's packaging, the flip-top cap on your toothpaste tube, the zipper on your jacket, the car, bike, or bus you took to school, the chair you sat in, the door handle you grasped and the hinges it opened on, and the ballpoint pen you used to take your test. Virtually every object that you see around you has passed through the hands of a mechanical engineer. Consequently, their skills are in demand to design millions of different products in almost every type of industry.

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