[thedoc]

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?
Asked by Neil Pariser


                                        Visit the webpage for the podcast in which this question is answered.

[chapter podcast=1093 track=08.07.20/Naked_Scientists_Show_08.07.20_1976.mp3]  ...or Listen to the Answer[/chapter] or [download as MP3]

[Madidus_Scientia]

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.

[Pumblechook]

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.

[lyner]

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".

[neilep]

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 !

[DoctorBeaver]

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.

[ukmicky]

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 !

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.  []

[DoctorBeaver]

And he'd had a dump!

[lyner]

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 . .

[thedoc]

Listen to this question on our podcast by clicking here

[ksc91u]

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.

[Don_1]

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  [)]

[lightarrow]

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.

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).

[ksc91u]

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).

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?

[lightarrow]

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).

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.

[Lawrence Skarin]

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.

[DanD]

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. 

[imatfaal]

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

The mass of a body is a measure of its energy-content; if the energy changes by L, the mass changes in the same sense by L/9 × 1020, the energy being measured in ergs, and the mass in grammes.

-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

[Stu]

Surely trapping electrons (1) will amount to mass or weight ?