Toothy: How Are Gears Used to Change Movement From One Direction to Another?

Problem

How are gears used to change movement from one direction to another?

Materials

• modeling clay
• 12 round toothpicks
• 2 pencils

Procedure

1. Slightly flatten two walnut-sized balls of clay to form two wheels.
2. Stick six toothpicks into the sides of each clay wheel. Be sure the toothpicks are evenly spaced around the clay pieces.
3. Form gear A by pushing a pencil through the center of one clay wheel.
4. Hollow out the hole with the pencil so that the clay wheel easily turns around the pencil
5. Form gear B by inserting a pencil through the center of the second clay wheel.
6. Squeeze the clay around the pencil so that the clay piece and the pencil turn together.
7. Place gear A on a table; hold the pencil vertically to keep the gear in place.
8. Hold gear B in a vertical position with its toothpicks between the toothpicks of gear A, as indicated in the diagram. Note: The pencil should be horizontal.
9. Rotate the pencil of gear B in a counterclockwise direction.
10. Observe the direction of movement of gear A.

Results

Gear B rotates vertically in a counterclockwise direction; the teeth of the two gears push against each other, causing gear A to rotate horizontally in a clockwise direction.

Why?

Gears are wheels with teeth around the outer rim. When the teeth of two gears fit together and one gear turns it will cause the other gear to turn. In this experiment, the toothpicks in the clay wheels act as gear teeth. When the gears are of equal size and have the same number of gear teeth, as in this experiment, they both turn at the same speed. Fitting the gears together at an angle changes the direction of rotation of the two gears.

Let's Explore

1. Would the number of toothpicks affect the results? Repeat the experiment, placing four toothpicks in each clay wheel. Repeat the experiment again, this time placing eight toothpicks in each clay wheel. Make an effort to turn gear B at the same speed for each experiment.
2. Would a different number of gear teeth in each wheel affect the results? Repeat the original experiment, placing eight toothpicks in the first wheel and four toothpicks in the second wheel. In order for the gear teeth to fit together, break the four toothpicks used in the second wheel in half; this makes the distance between the gears of both wheels nearly the same. Color one of the toothpicks on each wheel to make it easier to count the turns of each wheel.

Show Time!

1. Construct a model of gears with different numbers of teeth to demonstrate how gears change the speed of parts being moved. Trace the gear wheels in the diagram on a sheet of paper. Glue the paper to a piece of cardboard, and cut out the gears with scissors. Place the gears onto a second piece of cardboard, fitting the gear teeth together. Insert a small nail through the center of each gear, securing the gears to the cardboard so they will turn around easily. Determine the direction that each gear turns and the number of times the small gear turns when the large gear turns once.
2. Use an eggbeater to demonstrate how gears can change the speed and direction of movement. Use a small piece of tape to mark one blade and the wheel so that you can count the turns of each wheel easily.

Check It Out!

There are four major types of gears: spur gears, rack-and-pinion gears, worm gears, and bevel gears. Find out how each gear type regulates the speed and direction of motion.

This article is brought to you by:

From this Book:

Janice VanCleave's Machines
Buy this book »