 |
Science QuestionsThe Naked Scientists: Science Radio & Science Podcasts |
|
|||
 Science Questions RSS Feed |
Click here to listen
|
Will an iPod weigh more when it's full of music?I have a brand new iPod. It’s 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? Neil Pariser |
|
It will, Neil, if you fill it with heavy metal (!)
But really, the answer’s no. The way in which an iPod works depends on which one you’ve got. If you’ve got the one which is solid state memory then all it’s doing is binary data. It’s just a memory chip which is storing information as digital information. If you’ve got the older, bigger iPods that have hard-discs in them this is magnetic binary data. In each case it’s either storing a 1 or a 0 by having something pointing in one direction – a piece of magnetism pointing one way or the other, effectively. You can think about it like that. That doesn’t actually matter whether it’s actually got anything stored on it or not because storing nothing still weighs the same as storing something. It’s not like a cupboard that you’re putting tins into. On our forum, Madidus Scientia, put this very well when they said it’s a bit like having a handful of coins and they’re either heads or tails. That’s like the 0 or 1 in digital binary. They weigh the same whether they’re all showing heads or they’re all showing tails. There’s 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, this is the best excuse for not doing P.E. at school, when you run in both cases the hot kettle or you running have more energy. When you’re running faster you have more kinetic energy. Because E=MC2 – that’s E, energy, equals M, mass, times the speed of light, C, squared. Since the speed of light, C, doesn’t 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. You could use this as an excuse for not doing exercise. Similarly, in your iPod when you charge it up you’re putting energy into the battery. It will weigh a rather tiny amount more. One statistic I did hear is that a thumb print 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 weight of the battery will increasing due to charging it! |
|
July 2008 |
|
Neil Pariser asked the Naked Scientists:
If I get a brand new iPod at the store which has neither a charged battery or any data on it, does the iPod weigh the same after charging the battery and filling it with music and assorted pictures?
What do you think?
- Neil Pariser - 15th Jul 08
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 - 15th Jul 08
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. Writing data to 'new' (maybe unformatted) flash memory involves injecting tiny currents so there may be a very very small but finite increase in weight. Deleting may just prepare the memory for over- writing and not remove the charge on the gates of the Mosfets. - Pumblechook - 15th Jul 08
M-S's argument involves the E = mc2 argument and must be right. A similar argument around the memory elements could take you either way - does a 1 correspond to more or less energy than a 0? That has to depend on what logic technology is used. The total system would have to be electrically neutral before and after your 'injection' of currents so there would be no mass added or taken away. I think, basically the answer to the original question is "No". - lyner - 15th Jul 08
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 !! Glad I could help ! - neilep - 15th Jul 08
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 - 15th Jul 08
Neil I dont believe YOU Can i ask ,did you check to see if your car battery was in the same state of charge on both occasions. No i bet you didnt ? This may obvious but in between your trips did you refill your car with petrol so it had the same amounts whilst sitting on the weigh bridge ? Also was it sunny on your second trip , did you look into whether a car weighed more if its body was warmed by the sun. And i bet you didn't remove all those the flakes of skin and hairs that fell off your body in between trips. - ukmicky - 15th Jul 08
And he'd had a dump!
- DoctorBeaver - 15th Jul 08
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 - 17th Jul 08
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. And I thought E=MC2 only works when nuclear reaction taken place. After searching through Wikipedia, I found out that, the formula works even with normal chemical or physics reaction. Physics, for instance, when something speeds up, its would gain more mass. And when you charge the battery, electron moves from a track of an atom to another track of another atom. Then the electron moves faster(probably..), and because it moves faster, it gains weight. That is my explain to this. - ksc91u - 16th Sep 08
There is a difference in weight when downloading music files, especially if you are down loading heavy metal or rock; The equation is quite simple, vis: M + V(ΘΘΨΦδ x ωλ8 ) Σ + #of downloads : XL5 = Bullshit - Don_1 - 17th Sep 08
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 - 18th Sep 08
Do you mean that if we let a current flow over a wire, the weight of the wire would also increase? When a current flow over a wire, electrons are moving faster? than when they are on the track, right? - ksc91u - 18th Sep 08
Do you mean that if we let a current flow over a wire, the weight of the wire would also increase? When a current flow over a wire, electrons are moving faster? than when they are on the track, right? What I mean is that an electromagnetic wave can convey energy as well, you don't need to think about masses or charges exclusively. If you heat the battery with a flame or with a hot lamp, you increase its mass; if you send a light beam inside of it, you increase its mass, and so on. - lightarrow - 18th Sep 08
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 - 31st Mar 10
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. An object has potential energy, including the potential of converting its mass to energy. This is what E=mc^2 means, it is a method of determining the potential energy that would result from completely converting the existing mass to energy, not a formula for indicating that the mass changes when energy does. Increasing an object's energy using other techniques (gravitational, electric, thermal, chemical, whatever) does not convert said increase into mass. Mind you, it is possible that some of these increases might add mass, but only by the expedient of adding something material to the system. For chemical it might be atoms pulled out of the air, for electrical it might be additional charge carriers. In neither case is the mass increase related to the E=mc^2 forumla. Unless you have a nuclear (or anti-matter) reaction occuring there is no conversion between energy and mass, and therefore no change in total mass. - DanD - 7th Nov 11
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
See the whole discussion | Make a comment-taken from the original paper that caused all the trouble DOES THE INERTIA OF A BODY DEPEND UPON ITS ENERGY-CONTENT? By A. Einstein September 27, 1905 link here there is also a great wikipedia page on mass energy equivalence linked here with great real world practical examples (coiled spring ha greater mass when compressed, spinning bowling ball has greater mass more etc) and back to the op - there are those that say that the information and entropy involved will also lead to higher and lower energy states which will increase/decrease mass - although that is very debatable and is dependent on the state of the disc before and after - imatfaal - 8th Nov 11
| |
Twitter
Facebook
Del.icio.us
Slashdot
StumbleuponInformation presented on this website is the opinion of the individual contributors and does not reflect the general views of the administrators, editors, moderators, sponsors, Cambridge University or the public at large.
The contents of this site are © The Naked Scientists® 2000-2012. The Naked Scientists® and Naked Science® are registered trademarks.