Neil Pariser asked:
I have a brand new iPod. Itís never been charged and has no data put on it. Will it weigh more after charging the battery and filling it with music and pictures?
It will, Neil, if you fill it with heavy metal (!)
But really, the answerís no. The way in which an iPod works depends on which one youíve got. If youíve got the one which uses solid state memory then all itís doing is storing binary data. Itís using a memory chip which is storing information as digital information. If youíve got the older, bigger iPods that have hard-discs in them, this is magnetic binary data. But in either case itís storing a "1" or a "0" by having something Ė such as a piece of magnetic material - pointing one way or the other.
So it doesnít actually matter whether itís actually got anything stored on it or not, because storing nothing still weighs the same as storing something. Itís not like a cupboard that youíre putting tins into. On our forum, Madidus Scientia put it very well saying, "itís a bit like having a handful of coins and theyíre all either heads or tails." Thatís like the "0" or "1" in digital binary. They weigh the same whether theyíre all showing heads or theyíre all showing tails. So thereís no reason to think there should be a difference in the actual weight.
However, when you charge the battery, you are adding energy and there is a relationship between energy and mass...
As Einstein said E=mc2, so when you boil your kettle or - and this is the best excuse for not doing P.E. at school - when you run, in both cases (the hot kettle or you running) you have more energy. When youíre running faster you have more kinetic energy. Because E=mc2 Ė thatís E, energy, equals m, mass, times the speed of light, c, squared, and since the speed of light, c, doesnít change, if your E, energy, goes up, your mass must go up.
So a hot kettle will weigh more, and when you run in P.E. you will gain something like 10-14g. This is not a prodigious weight-gain but it is nonetheless weight gain due to taking exercise!
Similarly, in your iPod, when you charge it up youíre putting energy into the battery and it will weigh a tiny amount more. In fact, one statistic we did hear is that a thumbprint applied to the front of the iPod in the form of, say, the grease on your thumb will weigh thousands of times more than the increase in the weight of the battery due to charging it...
It would weigh more by the most insignificant tiny unmeasurable amount after it has been charged, but no, the data has no weight. Think of holding a few coins in your hands, 2 showing heads, 1 showing tails. If you flip them all so that they all show tails they still weigh the same, but show different information. Madidus_Scientia, Tue, 15th Jul 2008
From simple physics I can't see that a battery will add weight when charged. If it were true then discharging would reduce its weight. Electrons flow from one plate through the external circuit (although individual electrons don't make the whole trip) and back to the other plate.. The exact same number will return to the battery. The diluted acid in a lead-acid battery will increase its weight when charged..a hydrometer measures this to check on the state of the battery...but the lead plates will lose weight and there will be no overall change. More esoteric physics(such as quantum mechanics) may suggest otherwise.
M-S's argument involves the E = mc2 argument and must be right.
As a firm believer in empirical study I drove to a public weigh station with a non charged and empty ipod.......weight of car plus non charged and empty ipod 1431kg..........I then charged up the ipod and filled it with songs and did the same....the result ? 1431kg....voila !!
I agree with Sophie & M-S. Using E=mc2, if the energy of the battery increases then m must increase to keep the equation balanced. DoctorBeaver, Tue, 15th Jul 2008
And he'd had a dump! DoctorBeaver, Tue, 15th Jul 2008
If the weighbridge was accurate to 1kg, that would correspond to a possible error of 10e17J. The ipod battery would store something like 1MJ. So . . lyner, Thu, 17th Jul 2008
The first time I heard this podcast, I thought your answer of E=MC2 might be wrong. Because charging the battery only move electron from one chemical to another. So the total mass should not change.
There is a difference in weight when downloading music files, especially if you are down loading heavy metal or rock;
Sorry but it's not this the reason. Even if there weren't any electron movements at all the battery's mass would increase the same because of the flux of electromagnetic field (which carries energy). lightarrow, Thu, 18th Sep 2008
Since all chemical electric energy storage (cells and batteries) have some irreversibility, I'd guess mass change (through venting of the cell) would swamp any other effects. Really admired the heads/tails analogy from a previous post. Lawrence Skarin, Wed, 31st Mar 2010
I know this is an older discussion, but this is the second time today I've encountered a mis-aprehension, so I figured I should correct it.
Dan - E=Mc^2 is mass energy equivalence not just mass energy conversion. Lightarrow is correct in his post and you are misunderstanding the majesty of einstein' vision
Surely trapping electrons (1) will amount to mass or weight ? Stu, Wed, 30th Mar 2016