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Project Summary

Difficulty	6
Time required	Average (about one week)
Prerequisites	You must be able to ride a bicycle and have access to a bike path.
Material Availability	You must have access to a multi-speed bicycle and bicycling safety gear.
Cost	Low ($20 - $50)
Safety	Minor injury possible. Wear all necessary bicycling safety gear, especially a helmet. Adult supervision is recommended.

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Sponsor

Sponsored by a generous grant from Seagate

Abstract

Objective

To determine which gear ratio setting on a bicycle will result in the highest speed.

Introduction

One of the first bicycles built was called a penny-farthing bicycle. It had a huge front wheel with pedals connected to it, and a smaller back wheel. In order to make the bicycle worthwhile to ride, the front wheel had to have a large diameter. Unfortunately, the issue with this design was that it was unsafe to ride.

Figure 1. An example of a penny-farthing bicycle. (Wikipedia, 2008.)

Click here to watch "Kart Racing by Ali and Paige." This video was produced by DragonflyTV and presented by pbskidsgo.org.

At the turn of the century, the penny-farthing bicycles were being replaced by the safety bicycle. The safety bicycle had two wheels of equivalent size. The design of the bicycle has not changed, in terms of essential parts, from that time until now. The bicycle is made of the following parts: the frame, a seat, the handlebars, two wheels of equivalent size, the brakes, the crank and pedal, and the chain and the gears.

The set of gears connected through a crank to the pedals is called the chain wheel and the set of gears connected to the rear wheel is called the free wheel. (You can see additional bicycle parts labeled in Figure 2, below.) The idea behind multiple gears is to allow the cyclist to change the distance the bicycle moves forward with each rotation of the pedal. For example, a low gear means the pedals rotate much faster than the wheels, making it easier to climb up hills. A high gear is the opposite, allowing the wheels to rotate more quickly than the pedals, which enables better cycling down hills. The distance that the bicycle moves forward depends upon the ratio between the chain wheel and the free wheel gears. To learn and understand how to calculate the gear ratio, refer to the Science Buddies science fair project Gears Go Round. You can calculate the gear ratio by counting how many teeth each gear has and dividing the number of teeth on the chain wheel by the number of teeth on the free wheel.

Cyclists adjust the gear ratio according to how fast they want to move, the type of path they are on, and the conditions of the path. Click the DragonflyTV link on the right to learn how two kart racers, Ali and Paige, investigate how gear ratio affects racing speed. Once you have watched the video, it will be your turn to apply what you saw! Find a good bike path on which to experiment with the gears and gear ratio of your bicycle. Remember to wear all of your safety gear, especially a helmet, during this science fair project.

Figure 2. This diagram shows the components of a standard bicycle. (Wikipedia, 2008.)

Terms, Concepts and Questions to Start Background Research

• Gear
• Gear ratio

Questions

• What is a gear?
• Where are other places, besides bicycles, that gears are used?

Bibliography

• Wikipedia Contributors. (2009, January 5). Penny-farthing. Wikipedia: The Free Encyclopedia. Retrieved January 5, 2009, from http://en.wikipedia.org/w/index.php?title=Penny-farthing&oldid=260052407
• TPT. (2006). Kart Racing by Ali and Paige. DragonflyTV, Twin Cities Public Television. Retrieved November 21, 2008, from http://pbskids.org/dragonflytv/show/kartracing.html

The following website describes the parts of a bicycle and how bicycles work:

• Brain, M. (2000, April 1). How Bicycles Work. Retrieved November 21, 2008, from http://adventure.howstuffworks.com/bicycle.htm

This website gives a good tutorial on gears:

• Brain, M. (2000, April 1). How Gear Ratios Work. Retrieved November 21, 2008, from http://auto.howstuffworks.com/gears.htm

Materials and Equipment

• Access to a bike path
• Multi-gear bicycle
• Bicycle speedometer or bicycle computer; both available online at www.amazon.com
• Adult volunteer
• Bicycle helmet and safety gear
• Lab notebook

Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies receives no consideration, financial or otherwise, from suppliers for these listings. (The sole exception is any Amazon.com or Barnes&Noble.com link.) If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

1. To start this science fair project, you should become familiar with the bicycle that you are using. You should know how and when to change the gear ratio.
2. Open the speedometer package. Read the operating instructions and learn how to mount it onto your bicycle. Test the speedometer or bicycle computer to see if it is accurate. Ride your bike a known distance and see if the reading you get is that distance. Do this a couple of times to make sure that you are getting accurate readings.
3. Find an appropriate bike path on which to do your testing.
   1. You want to make sure that there aren't a lot of people around, so you may have to do your testing at a time when the path is least likely to be busy, such as at daybreak. Have an adult volunteer accompany you to the bike path.
   2. Do not perform this experiment at sunset or in the dark.
   3. The path should have a curve, followed by a straightaway.
   4. The path should be long enough that you can see a difference when you test. Ride the path a few times to make sure that it takes 30–40 seconds to ride, and to familiarize yourself with the path.
   5. Note down in your lab notebook what the path is made of and the conditions of the path. For example, is the path rocky or slippery? These are the kinds of conditions that affect speed.
4. Start the testing. Put on all of the safety gear, especially the helmet. Find a comfortable pedaling rate. Try 60 rotations per minute (RPM). If this is too slow, then increase it until you find a level with which you are comfortable. Make sure that you are not pedaling so fast that you spin out on the curve. It's very important that you try to stick to this pedaling rate for the entire project so your results are accurate.
5. The speedometer should be cleared and ready to measure. Start at one end of the curve. Note the gear ratio in your lab notebook. Ride the path until you reach the end of the straightaway. Record the speed from the speedometer in your lab notebook.
6. Repeat step 5 two additional times. Record all data in your lab notebook. Make sure you take breaks in between each trial so that you're just as energetic for each one.
7. Change the gear ratio four more times and repeat steps 5–6 for each change. Try to choose gear ratios two above the original setting and two gear ratios below your original setting. Record all data in your lab notebook.
8. Plot your data on a bar graph.
9. How fast were you able to go? Which gear ratio proved to be the best?

Variations

• How does changing the pedaling rate affect speed and the gear ratios required?
• Try a different path. For example, if you did the original testing on a paved track, try riding on a dirt path. How does the path material affect speed and the gear ratios?
• Take a look at these other Science Buddies projects if you are interested in learning more about gears:
  1. Gears-Go-Round!
  2. Hey Gear Heads! The Physics of Bicycle Gear Ratios

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

Credits

Michelle Maranowski, PhD, Science Buddies

• This project is based on the following DragonflyTV episode: TPT. (2006). Kart Racing by Ali and Paige. DragonflyTV, Twin Cities Public Television. Retrieved November 21, 2008, from http://pbskids.org/dragonflytv/show/kartracing.html

Last edit date: 2009-01-04 10:14:00

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.			Mechanical Engineering Technician You use mechanical devices every day—to zip and snap your clothing, open doors, refrigerate and cook your food, get clean water, heat your home, play music, surf the Internet, travel around, and even to brush your teeth. Virtually every object that you see around has been mechanically engineered or designed at some point, requiring the skills of mechanical engineering technicians to create drawings of the product, or to build and test models of the product to find the best design.
	Precision Instrument and Equipment Repairer One of the basic truths in the universe is that objects tend to go from a state of higher organization to a state of lower organization over time. In other words, things break down, and when those things are precision instruments or equipment, they require the services of very specialized technicians to restore them to their working order. Precision instrument or equipment technicians often combine a love of music, medicine, electronics, or antiques with delicate mechanical repair work.

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