Snappy Science: Stretched Rubber Bands Are Loaded with Potential Energy!

A fun physics problem from Science Buddies

Observations and results
Did the rubber bands stretched to 30 cm launch farther than the other rubber bands? Did you see a linear relationship between the launch distance and stretch length when you graphed your data?

You input potential (stored) energy into the rubber band system when you stretched the rubber band back. Because it is an elastic system, this kind of potential energy is specifically called elastic potential energy. Elastic potential energy (measured in the unit joules) is equal to ½ multiplied by the stretch length ("x") squared, multiplied by the spring constant "k." The spring constant is different for every rubber band, but can be figured out (see "Welcome to the Guide to Shooting Rubber Bands" below). When the rubber band is released, the potential energy is quickly converted to kinetic (motion) energy. This is equal to one half the mass (of the rubber band) multiplied by its velocity (in meters per second) squared.

Using these equations, you can calculate the velocity of the rubber band right when it is released, and find that the velocity has a linear relationship with the stretch length. (Because the amount of time that the rubber band spends in the air is dependent on its initial height and force of gravity, and these factors should not change between your trials, then how far the rubber band flies depends on its initial velocity.) Consequently, after you graph your data, you should see a roughly linear relationship between the stretch length and the launch distance.

More to explore
What Is Energy? from Wisconsin K-12 Energy Education Program (KEEP)
Energy Conversions: Potential Energy to Kinetic Energy from FT Exploring Science and Technology
Welcome to the Guide to Shooting Rubber Bands: The Physics of Shooting by Tim Morgan
Rubber Bands for Energy from Science Buddies

This activity brought to you in partnership with Science Buddies

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1. 1. carpefishus 12:53 PM 4/5/12

Working at engineering firms taught me rubber band survival techniques. Imparting spin by stretching one side more that the other will not only greatly increase the accuracy but also the range.

Also, note that a rubber band at ambient temperature will heat up when stretched and cool down relaxed. If you stretch it and let it loose heat while stretched, it will cool below ambient when relaxed. Fun stuff.

2. 2. AndersenWA@cox.net 09:06 AM 4/7/12

Interesting, but my guess is that the extra range is more due to imparting more potential energy into the rubber band by overstretching one side than you would if you streched both sides evenly. Is there any way to test that?

3. 3. mwl man 01:44 PM 4/7/12

I am 11years old and understand all the physics articles on scientific american yet this is harder than most of them.

4. 4. mwl man in reply to AndersenWA@cox.net 01:53 PM 4/7/12

I agree

5. 5. carpefishus 02:13 PM 4/7/12

I assume that it is the spin that does gives improvement to both the range and accuracy. Rubber band wars bear this out.

Accuracy: Spin give the band a predicable behavior. A non-spinning band flops a bit unpredictably.

Range: One side stretched has about half the potential energy of both sides stretched and even with only half of the energy it will have a much further range. I figure that the spin does aerodynamic tricks analogous to a golf ball spin.

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