All Work and No Play?
By John Cowens

This experiment using a ruler, thumbtack, rubber band and spring weight scale demonstrates how force works.

A machine is a tool that makes our work easier, and compound machines consist of several simple machines that work together. Technically, work is a force that acts on an object and moves it across a distance (Work = Force x Distance). Pushing, pulling and lifting are the main forms of work. Carpenters do work when they build objects out of wood, and gardeners do work when they plant seeds, pull weeds and harvest their crops. Machines make their work easier. For example, gardeners use shovels and hoes to break up weeds. The shovel and hoe are simple machines.

Below, you'll find a simple lesson that demonstrates how machines help us work, an explanation of force and a demonstration of work. The activities are appropriate for grades 2-4.

How machines help us
Machines help us in many ways. A pencil sharpener, the cord to raise and lower blinds and a doorknob are simple machines that have made our lives easier.

Materials

• electric mixer


• whipping cream


• two bowls


• sugar

Procedure

1. Pour the same amount of cream in each bowl.

2. Use a fork to make whipped cream. Have someone else use the electric mixer to whip the whipped cream. After two, four and six minutes, stop and check the progress of the fork and the electric mixer.
3. Add a little sugar to the cream and treat your whole class to some hot chocolate!

Ask your students to compare the results of the whipped cream race to man versus machine stories. You can integrate this activity with Language Arts by reading the books Paul Bunyan by Steven Kellogg (HarperTrophy, 1985, ISBN: 0-688-05800-0) and John Henry by Julius Lester (Puffin Books, 1999, ISBN: 0-140-56622-8).

Explaining force
Have students stand behind their moveable chairs and carefully push and pull them away from their desks. Pushing and pulling are examples of force. Every machine needs a force to make it work.

Materials

• thumbtacks


• rubber bands


• wooden rulers


• spring weight scale (measures grams)

Procedure

1. Lay the ruler on top of a piece of cardboard. Push the thumbtack halfway into the ruler on the left side.
2. Put the rubber band around the thumb tack and push it the rest of the way into the ruler.
3. Use the pulling force to stretch the rubber band 10 cm, 20 cm and 30 cm across the ruler. Use the spring weight scale to measure the force needed to stretch the rubber band. Which used the least amount of force? Which used the greatest amount of force?

Extension
Make a list of 10 things around the house that need force to make them work. List if it takes a push force or a pull force to work (examples: baby stroller, refrigerator door, etc.)

Work = Force x Distance
Work occurs when force moves an object. Ask your students if they think work occurred in these experiments.

Materials

• cotton balls


• pencils


• meter sticks


• masking tape

Procedure

1. Place an "X" on the floor with masking tape.
2. Place a cotton ball on the "X" and blow on it. Use a meter stick to measure the distance the cotton ball moves from the "X."
3. Place a pencil on the "X," flick it with your index finger and use a meter stick to measure the distance it moves from the "X."
4. Push down on the "X" with your feet. Can you measure the distance?

Recommended websites
Simple Machines
Edheads Simple Machines
Simple Machines Learning Site

Excellent books for your library
Simple Machines Starting With Science by Adrienne Mason and Deborah Hodge (Kids Can Press, 2000, ISBN: 1-550-74399-6).
Work & Simple Machines by Jon Richards and Ian Thompson (Copper Beech, 2000, ISBN: 0-761-31159-9).

John Cowens has taught for 26 years. He currently teaches sixth grade at Fleming Middle School in Grants Pass, OR.

January, 2005, Vol.35, No.4