# Rubber Band Science, by John Cowens

They can hold things together in a pinch, but did you know that rubber bands can also be used to teach the force of mass?

Not only are rubber bands great for binding objects together, but they can also be used in a simple science experiment that involves predicting, problem solving, measuring, graphing and experimenting.

Direct proportionality
Within the physical limits of rubber bands, there's a direct proportionality between added mass and rubber band length. The elasticity of rubber bands has a definite limit beyond which it can no longer stretch and eventually breaks.

In the experiment below, students observe the force of mass on a rubber band by adding equal increments of ten pennies. As this is being done, the independent variable (mass) should be graphed on the X-axis and the dependent variable (length) should be graphed on the Y-axis. Students should title the graph and label each axis with data represented and a scale.

Materials:
For each group of three or four students, the following materials are needed:

• one 1/4-inch wide rubber band
• one small plastic cup
• five large (50mm) paper clips
• 150 pennies
• a pencil
• a 12-inch (30 cm) ruler
• chart/graph handouts

Procedures:

1. Tell your students that they're going to test the stretch length of a 1/4-inch rubber band when a mass of pennies is added to it. Discuss the variables in this experiment. The mass applied is the independent variable and the distance stretched is the dependent variable.

2. Ask your students to arrange themselves in groups of three or four. Each group needs a Materials Manager, Recorder, Mathematician and Graph Designer.

3. To make the Mass Cup, students should push three of the large paper clips through the plastic cup equal distances apart at the rim. They then take the fourth paper clip and attach it to the top of each of these three paper clips and hang it across the lower end of the rubber band which will be tested. The fifth paper clip is used as a hook that will be attached to something sturdy, such as the top of a desk. Attach the hook to the top end of the rubber band.

4. Students should measure the length of the rubber band before placing 10 pennies in the Mass Cup. The kids should then record the length of the rubber band on the chart and graph.

5. Ask the Graph Designer in each group to make a chart and line graph for their group's data. They can label each axis on their graph, give each axis a scale and give their graph a title.

6. Students add 10 more pennies to the Mass Cup and record the length the rubber band is stretched. They can also record the data onto the chart and graph.

7. Students continue to add increments of 10 pennies to the Mass Cup, record the length that the rubber band stretches and record the data onto the chart and graph until all 150 pennies have been used.

Evaluation:

1. Did each group work to complete the experiments?

2. Is all the data charted and graphed?

4. What did they learn about proportionality?

5. What happened to the rubber band as increments of ten pennies were placed in the Mass Cup?

Variations:

1. Repeat and double the rubber band.

2. Freeze and/or bake rubber bands before testing.

3. Replicate the test with the same rubber band after it has been stretched to its elastic limit. Does the rubber band recover and respond with the same stretch length in the replicated test?

4. Replace the 1/4-inch wide rubber band with a 1/8-inch or a 1/16-inch wide rubber band and repeat the experiment.

LENGTH of stretched rubber band (mm)

John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.

Science