# Rubber bands give off heat when stretched: how much? **URL:** \ **Category:** Factual Questions\ **Created:** [October 2, 2012, 3:16am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451 "2012-10-02T03:16:23Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [October 2, 2012, 3:16am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/1 "2012-10-02T03:16:23Z")
See subject. For the sake of thread self-sufficiency, I’ve copied a passage from Wiki on [natural rubber](http://en.wikipedia.org/wiki/Natural_rubber) that complexifused me: In most elastic materials, such as metals used in springs, the elastic behavior is caused by bond distortions. When force is applied, bond lengths deviate from the (minimum energy) equilibrium and strain energy is stored electrostatically. Rubber is often assumed to behave in the same way, but it turns out this is a poor description. Rubber is a curious material because, unlike metals, strain energy is stored thermally. In its relaxed state, rubber consists of long, coiled-up polymer chains that are interlinked at a few points. Between a pair of links, each monomer can rotate freely about its neighbour, thus giving each section of chain leeway to assume a large number of geometries, like a very loose rope attached to a pair of fixed points. At room temperature, rubber stores enough kinetic energy so that each section of chain oscillates chaotically, like the above piece of rope being shaken violently. The entropy model of rubber was developed in 1934 by Werner Kuhn. When rubber is stretched, the “loose pieces of rope” are taut and thus no longer able to oscillate. Their kinetic energy is given off as excess heat. Therefore, the entropy decreases when going from the relaxed to the stretched state, and it increases during relaxation. This change in entropy can also be explained by the fact that a tight section of chain can fold in fewer ways (W) than a loose section of chain, at a given temperature (nb. entropy is defined as S=k\*ln(W)). Relaxation of a stretched rubber band is thus driven by an increase in entropy, and the force experienced is not electrostatic, rather it is a result of the thermal energy of the material being converted to kinetic energy. Rubber relaxation is endothermic, and for this reason the force exerted by a stretched piece of rubber increases with temperature. (Metals, for example, become softer as temperature increases). The material undergoes adiabatic cooling during contraction. This property of rubber can easily be verified by holding a stretched rubber band to your lips and relaxing it. Stretching of a rubber band is in some ways equivalent to the compression of an ideal gas, and relaxation is equivalent to its expansion. Note that a compressed gas also exhibits “elastic” properties, for instance inside an inflated car tire. The fact that stretching is equivalent to compression may seem somewhat counterintuitive, but it makes sense if rubber is viewed as a one-dimensional gas. Stretching reduces the “space” available to each section of chain. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [October 2, 2012, 4:08am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/2 "2012-10-02T04:08:19Z")
No idea how much heat it gives off, but who knew that stretching rubber bands would be the answer to reversing entropy? WAG though: I suppose the amount of force being put into stretching the rubber band as potential energy must be proportional to any heat it gives off. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [October 2, 2012, 11:46am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/3 "2012-10-02T11:46:00Z")
Here’s a reference to a paper on the amount of heat generated by stretching butyl rubber: [http://rubberchemtechnol.org/doi/abs/10.5254/1.3546779](http://rubberchemtechnol.org/doi/abs/10.5254/1.3546779) > [@](#): > > S. L. Dart and Eugene Guth (1945) Rise of Temperature on Fast Stretching of Butyl Rubber. Rubber Chemistry and Technology: December 1945, Vol. 18, No. 4, pp. 803-816. > > Abstract > > Study of the rise in temperature by fast stretching of Butyl gum and tread stocks throws considerable light on crystallization, internal friction, and carbon black reënforcement as functions of elongation and other possible variables. For low elongations, the low-heat curves show the occurrence of thermoelastic inversion. They show also that internal friction is much larger in Butyl than in Hevea. For high elongations the high-heat curves enable one to follow the late and abrupt crystallization so characteristic for Butyl stocks. The carbon black reënforcement of Butyl is followed for the whole range of elongations up to the breaking point. Specific carbon-black reënforcement takes place in the range of elongations before crystallization of the gum stock, but the shortening of the breaking elongation by the black excludes to a large extent the added reënforcement through crystallization. Physical measurements of the type reported in this paper serve a manifold purpose. They enable one to establish a correlation between physical properties and chemical structure. Such a correlation is simpler for fundamental physical properties, as the ΔT vs. ε curve, than for more complicated physical tests, as data from flexometer, which were designed to approach service conditions. Comparing different gum stocks with Butyl polymers among themselves and with Hevea or other synthetics, these measurements may guide the development of better Butyl polymers. Finally, comparing tread with gum stocks, they may help to recognize the nature of reënforcing by carbon blacks and the action of other compounding ingredients. Following its references, you get this one on measuring the heat of crystallization for natural rubber: [http://onlinelibrary.wiley.com/doi/10.1002/pol.1968.160061001/abstract](http://onlinelibrary.wiley.com/doi/10.1002/pol.1968.160061001/abstract) > [@](#): > > Rapid stress-induced crystallization in natural rubber > > J. C. Mitchell, > D. J. Meier > Abstract > Stress-induced crystallization in a rapidly stretched natural rubber gum vulcanizate has been studied using thermal techniques to follow the development of crystallinity. A special-purpose analog computer has been assembled and used on-line to process the thermal and mechanical data obtained in high speed tensile testing. Roughly first-order room temperature crystallization kinetics curves were obtained having time constants of 50–60 msec in the range of 400–540% extension. While the rate of this rapid, presumably primary crystallization appears rather insensitive to elongation in this limited range, the extent of crystallization at 400 msec increases smoothly from zero at 340% elongation to around 18% at 540% elongation. It is shown that our high-speed tensile tester can stretch this vulcanizate fast enough that most of the crystallization takes place after extension has been completed. Stress-strain curves obtained at this high rate are compared with those obtained at lower rates where crystallization takes place during the stretching. The articles aren’t available online, unless you have a subscription to the relevant journals. But you can go look them up at a college library. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [October 2, 2012, 11:57am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/4 "2012-10-02T11:57:12Z")
If the rubber were stretched say underwater what would be the volumetric change if say stretched 500%. Also how my hysterisis is measured when a stretched rubber returns to it’s relaxed state? And does the speed of relaxing it or how long it is held in the stretched state affect the hysterisis? ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [October 2, 2012, 3:18pm UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/5 "2012-10-02T15:18:58Z")
Perhaps I can point you in the right direction. The property you are looking for is the “loss modulus”. It’s a measure of how much energy is lost during deformation. Also known as the imaginary modulus, I think it’s similar to resistance and impedance (both only show up under oscillating conditions). It also depends on the type of rubber. Eg for tyres you want a low loss modulus, since they’re constantly being deformed, otherwise they’d waste fuel and heat up. ---
**Author:** ![Enlightening\_Meditation](https://avatars.discourse-cdn.com/v4/letter/e/ecc23a/32.png) [@Enlightening\_Meditation](https://boards.straightdope.com/u/Enlightening_Meditation)\ **Post date:** [October 2, 2012, 4:33pm UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/6 "2012-10-02T16:33:59Z")
I have noticed that tensile test specimens of high strength metal alloys became rather warm during ‘stretching’, i.e. axial loading applied and increased until fracture. I assume that this is a result of friction induced heat that’s generated between the microscope grain boundaries as the grains deform. It typically takes 20,000 to 60,000 pounds to pull a high strength steel tensile specimen to failure depending on the alloy, heat treatment history, and specimen size. So, this metal stretching requires far more power (heavy machinery) compared to that required to stretch rubber bands. Heat given off by a stretched rubber band is probably too negligible to be detected my human hands, but it would not surprise me if heat is given off. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [October 3, 2012, 5:04pm UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/7 "2012-10-03T17:04:17Z")
> [@Enlightening\_Meditation](#): > > Heat given off by a stretched rubber band is probably too negligible to be detected my human hands Possibly true for your hands, but you can detect it if you hold the stretched rubber band against your lips. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 3, 2012, 9:14pm UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/8 "2012-10-03T21:14:17Z")
> [@Xema](#): > > Possibly true for your hands, but you can detect it if you hold the stretched rubber band against your lips. Interestingly, stretched rubber cools down when it is allowed to unstretch. So if you stretch it, then hold against your lip, you will feel the warmth. If you keep it stretched and allow it to equalise with ambient temperature, then let it relax, aand put it against your lip, it will feel cold. One of the items on my project list is to try to make a working refrigeration system using rubber bands as the cooling cycle. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [October 4, 2012, 12:27am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/9 "2012-10-04T00:27:35Z")
> [@Mangetout](#): > > Interestingly, stretched rubber cools down when it is allowed to unstretch. > > So if you stretch it, then hold against your lip, you will feel the warmth. If you keep it stretched and allow it to equalise with ambient temperature, then let it relax, aand put it against your lip, it will feel cold. > > One of the items on my project list is to try to make a working refrigeration system using rubber bands as the cooling cycle. I don’t know if you can get useful refrigeration out of stretched rubber bands (I’ve done the experiment of cooling down the band many, many times), but you can work things the other way, and build a candle-powered (or lamp-powered) 'rubber band motor" that uses the temperature change to change the band tension, making a wheel revolve [![](https://img.youtube.com/vi/OW6aEmOsXv0/hqdefault.jpg "Rubber Band Heat Engine") ](https://www.youtube.com/watch?v=OW6aEmOsXv0) > **[How to Build a Rubber Band Heat Engine](https://www.instructables.com/How-to-Build-a-Rubber-Band-Heat-Engine/)** > > How to Build a Rubber Band Heat Engine: Hello Everybody! Have you ever wanted to impress your friends with a cool physics project? Well you're in luck!! My instructable will teach you how to build the simplest kind of heat engine. This instructable... ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [October 4, 2012, 12:49am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/10 "2012-10-04T00:49:51Z")
I just watched [Feynman on rubber bands.](http://www.youtube.com/watch?v=XRxAn2DRzgI&feature=youtube_gdata_player) He uses the analogy of a stretched string being constantly “bombarded with jiggly things,” to which the stretched part (which is what?) resists, producing heat. These are molecular or atomic? And why do they jiggle? ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [October 4, 2012, 1:29am UTC](https://boards.straightdope.com/t/rubber-bands-give-off-heat-when-stretched-how-much/636451/11 "2012-10-04T01:29:44Z")
I’ve found that the demo works nicely with a balloon, as there’s more area for lip contact.