Lesson 09 – Changing Direction: Worm Gears

Read About Worm Gears


Read the vocabulary terms to understand the reading better.

Bevel Gear

A bevel gear has teeth that are slanted.


Friction is a force created when things rub against each other and slows things down.


A gear is a wheel with teeth around it that slot together with other gears.

Spur Gear

A spur gear has a wheel with teeth around the outside and works when gears are in a straight line.

Worm Gear

A worm gear has just one tooth that spirals along a rod.

Changing Direction: Worm Gears

Spur gears and bevel gears have several teeth. A worm gear has just one tooth. The tooth spirals along a rod that looks a lot like the thread on a screw. A worm gear can be used to make a spur gear turn.

The diagram below shows a motor turning a worm gear. The worm gear makes the spur gear turn. The two gears turn at a right angle to each other. (Notice the direction arrows.)

You can use a worm gear to make a spur gear turn, but you cannot use a spur gear to make a worm gear turn. Friction will stop the gears from turning.

The toy clock below helps children learn to tell time. By turning the knob at the top, you make the clock’s hands move to show any time. This toy uses a worm gear and spur gears.

Now Show What You Know!

Complete some questions about the reading selection by clicking “Begin Questions” below.