Brief Description:

Students learn about gears through hands on exploration and a gear worksheet.

Grades: 3, 4, 5, 6, 7, 8

Time: 1 hour

Keywords: gears, gear ratios, driver gear, follower gear, gear train, simple machines, torque, rotation

Lesson Objectives

• Students will learn how gears work as simple machines
• Students will use their knowledge of gears to construct a gear train that can connect the gears on the challenge wall

Materials

• 1 Gear Kit per group:
• (5) 8-tooth gears
• (5) 12-tooth gears
• (5) 16-tooth gears
• (5) 24-tooth gears
• (5) 40-tooth gears
• (1) worm gear
• 10-20 axles pegs
• 20-30 bushings
• Challenge wall (This wall should be a collection of beams with holes. It should be about 4 inches tall and 6–8 inches wide. On the top right corner, attach a gear with an axle and a bushing)
• One gear activity worksheet per group

Procedure

1. Introduce Gears.
1. Gears are simple machines – a device that helps people do work. Gears connect to each other with interlocking teeth.
2. Because the gears are interconnected by these teeth, when one gear is rotated, the others rotate as well. The system of interconnected gears is called a gear train.
3. The drive gear is the first gear in a series of gear. It is the one that is typically connected to a power source. Follower gears are those that are moved by the driver gear.
2. Different sized gears have different numbers of teeth. A gear ratio is the number of teeth on the drive gear compared to the number of teeth on the follower gear. Teeth on drive gear: Teeth on follower gear.
3. Why do gear ratios matter? The difference in the number of teeth means that one turn of a big gear will turn a small gear more than one turn.
1. Gearing up means that for every revolution of the drive gear the follower gear turns more than one revolution. This is useful when you want to make something move faster and give less power to whatever is attached to the follower gear.
2. Gearing down means that for every revolution of the drive gear, the follower gear turns less than one revolution. This is useful for when you want to give more power to whatever is attached to the follower gear but it moves slower.
4. Gears are used to slow down or speed up motors in cars, give bikes more resistance up hills, make watch hands move at different speeds etc.
5. Pass out the gears to the students so they can have a close look.
6. Have students count the number of teeth on each gear.
1. Have students complete the Gear Ratio worksheet (see Resources)
7. Explain to students how when one gear is turned clockwise, the other gear turns counterclockwise.
1. Pass out the ‘Gears Worksheet’ (see Resources)
8. Introduce the Challenge Wall Activity. Students must add gears to the wall so that when you turn a driver at the bottom right, the gear located at the top right will turn.
1. Challenge Wall

Extensions and Modifications:

• Challenge Wall Modifications:

• When rotating the gear in the right corner, tell the students that it must rotate in a certain direction (clockwise or counterclockwise)
• Student must be able to complete the Challenge Wall activity with a certain number of gears

• Hand Mixer (Extension, 1 hour)

• Tell students that in this challenge they will be building a hand mixer.
• Show students different pictures and/or videos of hand mixers, explaining what they do and how they work.
• Tell them the requirements for their hand mixers. For example:
• Must have at least three gears
• Can be a manual or electric hand mixer
• Allow the class to brainstorm different ideas for their mixer design. Have them plan out and draw their design.
• Distribute materials and have students start building.
• After the students finish, review the activity with the class. Have them share their ideas, ask groups to explain what the hardest part of the challenge was, etc.

Resources:

### Tufts Student Teacher Outreach Mentorship Program • 200 Boston Ave. • Suite G810 • Medford, MA • 617-627-5888

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