A simple machine can be any device that requires only a single force. There are six general types of simple machines: levers, inclined planes, screws, wedges, pulleys and a wheel-and-axle system. These machines appear in many common objects, and they are easy to construct. They also offer a perfect medium for teaching fifth-grade science students about basic forces because they have a simple, easy-to-follow design, and you can easily turn them into a hands-on activity, which is more conducive to learning.

## Lever and Fulcrum

Bring a large, long board such as a 2-by-8 to class. Ask some of your students to lend you their science books, and set them up in an open space to act as a fulcrum. Set your board on top of them so that each arm of the "lever" is equal length.

Set a heavy object, such as another stack of books, on one end of the board -- this is called the "load arm." The other arm is the "force arm."

Have students push on the force arm to get a feel for how heavy it is. Move the lever further away on the fulcrum so that the load arm is longer. Have the students push again and compare the force needed. Move the lever closer so the force arm is longer, and have the students compare again.

## Water Wheel

Using a sturdy pair of scissors make eight slices in the edge of a pie tin, from the top of the edge to the floor of the tin.

Twist these edges to make blades. They should look like the blades of a windmill.

Push a pen through the center of the tin.

Set the water-wheel over a wide pan or sink and slowly pour a pitcher of water over it. Have the students observe how the force of the water moves the wheel. A pinwheel has a similar structure; you can make one from construction paper instead of a pie tin and simply blow on it.

## Inclined Planes

Purchase a set of toy cars and tracks, or have students bring them in if they have any. Make sure the tracks have different levels of inclination. You can also construct your own tracks with cardboard, foam board, plastic piping or stacks of books.

Set up a series of tracks with turns and variations in the level of inclination -- some very steep, and some almost flat.

Send some cars racing down the track, and have the students observe where the cars speed up and slow down. Ask them to pull cars up the track with a spring-scale to observe the different amounts of force needed at different levels of inclination.