Rubber Band Stretch

Students quickly stretch a rubber band and feel it become warm under the nose. After the stretched band returns to room temperature, they release it quickly and feel a brief cooling. The demonstration shows the thermoelastic effect in polymers: rapid stretching aligns chains and releases heat; rapid contraction increases disorder and absorbs heat.

1. Hold a thick rubber band near your upper lip (skin under the nose is sensitive to small temperature changes) to sense its initial temperature.
2. Quickly stretch the rubber band to 2–3 times its length and immediately place it just below the nose without touching the nostrils to feel the warmth.
3. Keep the rubber band held at that stretch for about 20–30 seconds so it re-equilibrates to room temperature while still stretched.
4. Release the tension quickly and place the relaxed band just below the nose again; you should feel a brief cooling.
5. Repeat once or twice to confirm the effect. Compare quick versus slow stretching to note how rate influences the temperature change.
6. Optional measurement: use an IR thermometer or a taped-on fine thermocouple to record the temperature spike on rapid stretch and the drop on rapid release.

• None available

• Compare different polymers (latex rubber band vs thick exercise band vs silicone band) for size of effect at the same stretch ratio.
• Hold at different stretch ratios (e.g., 150 percent vs 250 percent length) and record how the temperature change varies.
• Test rate effects: very fast stretch and release versus slow, steady changes.
• Map temperature with an IR camera if available, or place a tiny piece of thermochromic paper against the band.

• Keep rubber bands away from eyes and face; do not snap against skin. Safety glasses are recommended.
• Do not overstretch; stay within 2–3 times the original length to reduce breakage risk.
• Be aware of latex allergies; provide non-latex alternatives if needed.
• Discard cracked or dried-out bands that may break unexpectedly.
• Clean or replace bands between participants to maintain hygiene.

• Why does the band feel warm when stretched quickly? (Rapid stretching aligns polymer chains, reducing entropy; the material releases heat to the surroundings.)
• Why does the band feel cool when released after equilibrating? (Rapid contraction increases entropy; the material absorbs heat from nearby air/skin, creating a brief cooling.)
• Why is the effect stronger when the stretch or release is fast? (Fast changes are closer to adiabatic, limiting heat exchange with the environment, so the temperature change is larger.)
• How would slow stretching and slow release feel? (Little or no temperature change because heat has time to flow to or from the surroundings.)
• What variables should you keep constant to compare trials fairly? (Initial band, stretch ratio, hold time before release, ambient temperature, and measurement position.)