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Name of Activity Bicycle Unit: Bike Gears
Author STOMP
Keywords bicycle, gear ratios, gears, gearing up, gearing down, teeth, cogs, drive gear, follower
Subject Non-LEGO
Grade Level 4, 5, 6
Time 1 Hour Total
Brief Description Students will be introduced to gears using a real bike as an example. Students will use this knowledge to do an activity about gear ratios.
Lesson Objectives: - To relate the concepts of gears, gear ratios, and gearing up and down to actual bikes.
Materials Needed: - At least one road bike.
- As many trainers as bikes.
- Measuring tape.
- Activity worksheets.
Preparation and Set Up: - Set up the bike(s) on the trainer(s).
- Place a mark on the rear wheel using tape or chalk.
- Make enough worksheet copies for each student.
- Arrange students in groups if there is more than one bike to look at.
Necessary Background Gears are wheels with teeth, or cogs. These teeth come in contact with each other and interlock so that when one gear turns the other gear also turns. Interlocking gears of different sizes turn at different rates. The gear that is manually turned is called the drive gear. The other gear is connected to a wheel or axle that needs to be turn; this is called the driven gear or follower.

On a bike, gears are connected by a chain. The driver is the gear connected directly to the pedal. The back wheel of the bike is connected to the pedal by a chain. Usually there is a mechanism on the handle bars that changes the gear ratio; in other words, moves the chain to gears of different sizes on the driver and driven gears.

Gear ratios are a set of two numbers that tell how fast one gear will spin in relation to the other gear. A gear ratio is a direct function of the number of cogs on each gear. To calculate a gear ratio, count the number of teeth on the drive gear and divide it by the number of teeth on the driven gear.

Bicyclists gear up and down depending on the conditions of where they are riding. Gearing up is when a bicyclist chooses a high gear ratio; there are more teeth on the drive gear than then driven gear. This means that you go very far on one pedal, but can be good when you want to climb hills. This is because with one pedal, the wheel on the back gear spins several times. Gearing down is when a bicyclist chooses a low gear ratio and there is a lower gear ratio closer to 1:1. This means that for each pedal the rear wheel turns a lot; a bicyclist can not go far, but each pedal provides more power. Gearing down is good for going uphill, or just starting out.

Vocabulary:
Gears
Cogs
Teeth
Gear Ratio
Drive Gear
Driven Gear
Gear up
Gear down

Procedure
  1. Choose the large gear in the front, and the small gear in the back.
  2. Have the students count the number of cogs on both gears.
  3. Slowly turn the pedal one time and see how many revolutions the rear wheel makes (using the marker on the rear wheel to see the revolutions).
  4. Calculate the gear ratio by dividing the number of cogs on the front gear by the number of cogs on the rear gear.
  5. Based on the fact that circumference = 2*pi*radius determine how far the bike would have gone in one revolution of the pedal
    1. Measure the radius of the wheel.
    2. Multiply the radius by 2*pi (6.28).
    3. Multiply this number by the number of revolutions that the wheel made for one pedal.
  6. Have students fill out the attached worksheet for different gear ratios.
  7. Demonstrate cadence and ease of pedaling for each setting.
  8. When the students have completed the worksheet, bring the class together for discussion. Ask students:
    1. What happened to teh gear ratio as the rear gear got larger adn larger?
    2. Did that make it easier or harder for the cyclist to pedal?
    3. Which of the tested gear ratios would you want to use to climb a big hill?
    4. Which of the tested gear ratios would you want to use to go down a hill really fast?
Extensions or Modifications: - Have students calculate how far a person’s feet travel in one rotation (circumference of the circle that you foot would make in the air using the length of the pedal as the radius).

- Have students use the gear ratios to calculate how far a bike can go with one pedal in a high gear ratio (e.g. 1 to 4, or a low gear ratio 1 to 1).

Reference 1 http://sites.tufts.edu/stompactivitydatabase/files/formidable/gear1.pdf
Reference 2 http://sites.tufts.edu/stompactivitydatabase/files/formidable/gear2.doc
Reference 3 http://sites.tufts.edu/stompactivitydatabase/files/formidable/gear3.pdf
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