Introductory Force Experiment

(uses rubber bands, plastic bag, paper clips, measuring strip, which you should have received after purchasing the CD's as directed)

See the Introductory Force Experiment video clip on the GEN 1 CD, then proceed as follows:

Set up the experiment and collect data:

• Use your calibrated rubber band, being careful that it has not yet been stretched out, and under no circumstances allow the rubber band to stretch out to more than its maximum calibrated length.
• Hang the rubber band from a support (e.g., a table edge) as demonstrated on the video clip, using a paper clip bent into an appropriate shape. As shown on the video clip, suspend the plastic bag from the other end of the rubber band using another paper clip. Measure the length of the rubber band.
• Carefully add 1/4 cup of water to the plastic bag, being careful not to spill any, and measure the length of the rubber band from clip to clip. If you don't have a 1/4-cup measuring cup you may use four full tablespoons for 1/4 cup.
• Add another 1/4 cup of water and again measure the length in the same manner.
• Repeat until the rubber band reaches its maximum calibrated length.

Organize and graph your information:

• Make a table of rubber band length vs. number of 1/4 cups of water in the bag.
• In the mini-experiment that goes with this experiment you constructed a graph of force vs. length for your calibrated rubber band.  Using the curve you drew on that graph determine the force exerted by the rubber band as it supports one, two, three, ..., quarter-cups of water.

Think about what's going on here:

• What makes the rubber band stretch?
• Why does the rubber band stretch more when more water is added to the bag?

Submit your results:

Describe any clever things you might have done to obtain accurate results.

Give your table of # of quarter-cups vs. length.

Give the results you obtained from the calibration graph for the forces exerted by 1, 2, 3, ... quarter-cups of water.

The graph shown below depicts force vs. length for a rubber band that was stretched way too far.  Its force characteristics were altered by over-stretching and it will not be useful in future experiments, but the curve is interesting and consistent so it is shown here.