Exploring the Physics of Stretching a Rubber Band

[abcd8989]

Why a rubber band gets warmer when repeatedly stretched and relaxes? Where does the gained ME comes from? Besides, does rubber band obeys Hooke's Law?

 

[Mapes]

Any temperature increase after stretching and releasing would be due to internal friction, from polymer chains moving past each other. And every solid obeys Hooke's Law for small enough deformations. Take a look at a stress-strain curve for rubber to see how its stiffness changes as you stretch it.

 

[Dickfore]

 

[Oldfart]

Any temperature increase after stretching and releasing would be due to internal friction, from polymer chains moving past each other. And every solid obeys Hooke's Law for small enough deformations. Take a look at a stress-strain curve for rubber to see how its stiffness changes as you stretch it.

I kinda thought it was due at least in part to thermodynamics. Try this: Get a largish rubber band, stretch it tightly (using both hands) while holding it against your upper lip. It will feel warmer right after the stretch. Now move the rubber band away from your lip but keep it stretched, hold it that way for maybe 30 seconds or so. Then hold it aginst your lip again and immediately relax the stretch and it will feel cool. The cooling wouldn't be due to friction, right?

 

[abcd8989]

So what is the true rational behind? And does it have something to do with elastic hysteresis?

 

[Dickfore]

No, and the question you had asked does not correspond to reality. If you relax a stretched rubber band it should cool.

 

[Mapes]

I kinda thought it was due at least in part to thermodynamics. Try this: Get a largish rubber band, stretch it tightly (using both hands) while holding it against your upper lip. It will feel warmer right after the stretch. Now move the rubber band away from your lip but keep it stretched, hold it that way for maybe 30 seconds or so. Then hold it aginst your lip again and immediately relax the stretch and it will feel cool. The cooling wouldn't be due to friction, right?

No, and the question you had asked does not correspond to reality. If you relax a stretched rubber band it should cool.

The original question was about a rubber band that was "repeatedly stretched and relaxe[d]". You're both focusing on the second half, the relaxation, in which the polymer chains are allowed to re-kink and re-coil, increasing their configurational entropy. But over the complete cycle, the configurational entropy is unchanged. Any temperature increase must be due to friction.

 

[Isaacsname]

I can't believe you people have me stretching rubber bands on my lips . What's next ?

" I put some salt in my eye and was wondering... ":tongue2:

I noticed that the faster the stretch, the more heat generated, I understand that, ...the cooling,...I noticed the rubberband , when relaxed against the lip, tends to draw the skin together in tiny folds as it relaxes, might there me some slight loss of heat transfer by conduction, in the form of less surface area contact between lip and rubber band ?

One would think that if the rubber were making surface contact on the relax, like it is when you are initially stretching it, it would generate a slight amount of heat from friction.

If you stretch the band out, let it cool, then draw it across your lip, you will sense the slight rise in temp from friction.

I read somewhere's that our lips are the most temperature sensitive area on our bodies, would they be able to discern such a small difference in temperature ?

Now, excuse while I go find my chapstick, this has been ...taxing