# Weight difference between fully charged and discharged phone

**URL:** https://boards.straightdope.com/t/weight-difference-between-fully-charged-and-discharged-phone/947319
**Category:** Factual Questions
**Created:** [July 26, 2021, 11:49am UTC](https://boards.straightdope.com/t/weight-difference-between-fully-charged-and-discharged-phone/947319 "2021-07-26T11:49:30Z")
**Posts on this page:** 1
**Page:** 3

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### Author: ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)
#### Post date: [August 28, 2021, 1:25pm UTC](https://boards.straightdope.com/t/weight-difference-between-fully-charged-and-discharged-phone/947319/42 "2021-08-28T13:25:12Z")

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> [@CookingWithGas](#):
>
> The heat is a product of the internal friction of the molecules as the band is twisted.

No. If that were true, you’d get heat from “internal friction” when the rubber relaxes. But contraction is endothermic. The stretched state has lower entropy.  
Likewise, rubber contacts when heated and expands when cooled.  
More here, designed for kids:

> **[Energy and Entropy of a Stretched Rubber Band | Energy Foundations for High...](https://highschoolenergy.acs.org/energy-theories/energy-entropy-rubber-band.html)**
>
> An inquiry-based lab investigation from Energy Foundations for High School Chemistry.

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