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  1. #1
    oleum perdisti
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    Ultimate weight weenie question

    Okay, maybe it isn't the ultimate, and maybe it aint too original, I don't know, but here goes.

    Does the state of charge affect the mass/weight of a battery ?

    In other words, can I lighten my ride by having more or less charge in the battery to my headlight?

    I know that if there is any difference, it would be pretty negligible, but it's been a long time since my college physics days and this thought occured to me during a recent ride, so rather than look it up myself, I thought I'd submit my question here for any resident physics nerds.
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  2. #2
    chips & bier
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    Nope

    Quote Originally Posted by drsam
    Okay, maybe it isn't the ultimate, and maybe it aint too original, I don't know, but here goes.

    Does the state of charge affect the mass/weight of a battery ?

    In other words, can I lighten my ride by having more or less charge in the battery to my headlight?

    I know that if there is any difference, it would be pretty negligible, but it's been a long time since my college physics days and this thought occured to me during a recent ride, so rather than look it up myself, I thought I'd submit my question here for any resident physics nerds.
    It's kinda like clearing your mind before a race. It helps, but not from a weight standpoint.

  3. #3
    oleum perdisti
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    Quote Originally Posted by eric
    It's kinda like clearing your mind before a race. It helps, but not from a weight standpoint.
    Are you sure about that.

    When I discharge a battery via the light, photons are emited.

    As I said, physics was a long time ago, so I can't remember if a photon has any mass or not, but I think an electron does have mass.

    Those photons are created by the passage of electrons through the bulb filament causing it to heat up and give off energy in the form of heat and light (photons).

    These electrons flow from the negative terminal of the battery, through the wires and the bulb and into the positive terminal of the battery.

    In the process, energy is lost. We feel it being lost in the heat of the bulb and see it being lost in the light emitted.

    If I remember correctly, the laws of conservation of energy and matter state that energy and matter can neither be created nor destroyed. Their form can only be changed and mass can be converted to energy and vice versa.

    If our lighting system is losing energy in the form of heat and light being emmited, then using the equation E=MC2 (E=MCsquared), it seems to me that if the E part (energy) gets smaller, then the M part (mass) has to also get smaller in order for the equation to remain balanced.

    Therefore it would seem to me that a fully charged battery should weigh more than a fully drained battery.

    I'm not sure about this though.

    Any physics nerds about?
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  4. #4
    Ole
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    Heard of Einstein?

    Quote Originally Posted by drsam
    Are you sure about that.

    When I discharge a battery via the light, photons are emited.

    As I said, physics was a long time ago, so I can't remember if a photon has any mass or not, but I think an electron does have mass.

    Those photons are created by the passage of electrons through the bulb filament causing it to heat up and give off energy in the form of heat and light (photons).

    These electrons flow from the negative terminal of the battery, through the wires and the bulb and into the positive terminal of the battery.

    In the process, energy is lost. We feel it being lost in the heat of the bulb and see it being lost in the light emitted.

    If I remember correctly, the laws of conservation of energy and matter state that energy and matter can neither be created nor destroyed. Their form can only be changed and mass can be converted to energy and vice versa.

    If our lighting system is losing energy in the form of heat and light being emmited, then using the equation E=MC2 (E=MCsquared), it seems to me that if the E part (energy) gets smaller, then the M part (mass) has to also get smaller in order for the equation to remain balanced.

    Therefore it would seem to me that a fully charged battery should weigh more than a fully drained battery.

    I'm not sure about this though.

    Any physics nerds about?
    Some bicycle dude named Einstein contemplated this a lot, and came up with the little known formula E=mc^2.

    The mass of the battery is slightly higher when charged because it contains more energy, but the change in mass is tiny. Very, very tiny. I doubt there are scales that could measure it.

    Ole.

  5. #5
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    Ha ha Einsteiners. E=mc squared also means that as you increase speed your mass increases. At the speed of light mass is infinite and that's why you can't go any faster. So slow and you'll get lighter, with your discharged battery.

  6. #6
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    Folks this is a chemical reaction, so the physicist can sit this one out. E=Mc^2 shows the relationship between mass and energy.

    Anyway this french chap worked this out before he lost his head in the French revolution. Sorry for the history lesson, but you do not lose mass in a chemical reaction.

    http://en.wikipedia.org/wiki/Antoine_Lavoisier

    In other words if your battery is thermonuclear one its mass will be identical. I have strong doubts you are using a thermonuclear battery.

    Caveat** If it is a lead acid battery it will give off of H2 as it discharges, but it is such a small mass that it is not significant.

    Again this is chemistry not physics. You start out with molecules in a high energy state [charged battery] and end it with ones in lower energy states [discharged battery].

  7. #7
    oleum perdisti
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    Quote Originally Posted by ExtraStout
    Folks this is a chemical reaction, so the physicist can sit this one out. E=Mc^2 shows the relationship between mass and energy.

    Anyway this french chap worked this out before he lost his head in the French revolution. Sorry for the history lesson, but you do not lose mass in a chemical reaction.

    http://en.wikipedia.org/wiki/Antoine_Lavoisier

    In other words if your battery is thermonuclear one its mass will be identical. I have strong doubts you are using a thermonuclear battery.

    Caveat** If it is a lead acid battery it will give off of H2 as it discharges, but it is such a small mass that it is not significant.

    Again this is chemistry not physics. You start out with molecules in a high energy state [charged battery] and end it with ones in lower energy states [discharged battery].
    This is sort of approaching the answer I was expecting, but let me ask you this,

    When the battery is plugged into the wall outlet and charged, exactly what (from the chemistry viewpoint) occurs?
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  8. #8
    Ex-Gunslinger
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    Have you tried checking the weight before and after charging your battery? I would imagine you would save more weight by having a good nose blow before you ride.

  9. #9
    Ole
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    Quote Originally Posted by ExtraStout
    Folks this is a chemical reaction, so the physicist can sit this one out. E=Mc^2 shows the relationship between mass and energy.

    Anyway this french chap worked this out before he lost his head in the French revolution. Sorry for the history lesson, but you do not lose mass in a chemical reaction.

    http://en.wikipedia.org/wiki/Antoine_Lavoisier

    In other words if your battery is thermonuclear one its mass will be identical. I have strong doubts you are using a thermonuclear battery.

    Caveat** If it is a lead acid battery it will give off of H2 as it discharges, but it is such a small mass that it is not significant.

    Again this is chemistry not physics. You start out with molecules in a high energy state [charged battery] and end it with ones in lower energy states [discharged battery].

    Not so. More energy = more mass. Even in chemical reactions. Where else does the energy come from? High energy state = more mass, low energy state = less mass. Look it up.


    Ole.

  10. #10
    oleum perdisti
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    Quote Originally Posted by Laika
    Have you tried checking the weight before and after charging your battery? I would imagine you would save more weight by having a good nose blow before you ride.
    I would agree completely.

    This is really meant as a theoretical fun sort of query, not really intended for any sort of practical application.

    For the amount of weight difference (if any, since that is the question), I'm quite certain that I could never in a lifetime be able to afford the sort of ultrasensitive scale that would be required to make this measurement (if indeed such a precise scale even exists).
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  11. #11
    oleum perdisti
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    Quote Originally Posted by Ole
    Not so. More energy = more mass. Even in chemical reactions. Where else does the energy come from? High energy state = more mass, low energy state = less mass. Look it up.


    Ole.
    I'm not so sure this is exactly right. Hence my reply asking about exactly what goes on during the charging process in a battery.

    My suspicion, and I'm no expert is that extra stout may be right.

    My suspicion is that when you plug your battery into the wall, you are feeding electrons into the negative part of the battery, which ideed does increase the energy state and the mass of the negative part of the battery, but I suspect that you concomitantly remove an equal number of electrons (and mass) from the positive part of the battery, for a net change in mass of zero.

    I'm not entirely sure about this though.

    One thing I don't agree with stout on is his insistance that this is all Chemistry and not physics.

    I personally don't draw a clear distinction between the two. I think they are fairly heavily overlapping disciplines.
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  12. #12
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    Quote Originally Posted by drsam
    My suspicion is that when you plug your battery into the wall, you are feeding electrons into the negative part of the battery, which ideed does increase the energy state and the mass of the negative part of the battery, but I suspect that you concomitantly remove an equal number of electrons (and mass) from the positive part of the battery, for a net change in mass of zero.
    Bingo. It is chemistry. Antoine Lavoisier’s experiments proved the conservation of mass in the 1700’s.
    C + 02 → C02
    Lead acid cells:
    Pb + HSO4- → PbSO4 + H + + 2e -
    PbO2 + 3H + + HSO4- + 2e - → PbSO4 + 2H2O

    Each is a balanced equation, and there is no loss of mass. Think of rechargeable chemical batteries as energy containers. In a nutshell you charge electrons from one electrode and discharge electrons from the other electrode.

    Quote Originally Posted by drsam
    One thing I don't agree with stout on is his insistance that this is all Chemistry and not physics.

    I personally don't draw a clear distinction between the two. I think they are fairly heavily overlapping disciplines.
    I will give you that, and they are related. Since we are talking about reactions in which mass it conserved I called it Chemistry. Long ago, about 100 years ago, Chemistry and Physics were separate studies. However I am not that old.

  13. #13
    Ole
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    You're leaving out the energy

    Quote Originally Posted by ExtraStout
    Bingo. It is chemistry. Antoine Lavoisier’s experiments proved the conservation of mass in the 1700’s.
    C + 02 → C02
    Lead acid cells:
    Pb + HSO4- → PbSO4 + H + + 2e -
    PbO2 + 3H + + HSO4- + 2e - → PbSO4 + 2H2O

    Each is a balanced equation, and there is no loss of mass. Think of rechargeable chemical batteries as energy containers. In a nutshell you charge electrons from one electrode and discharge electrons from the other electrode.



    I will give you that, and they are related. Since we are talking about reactions in which mass it conserved I called it Chemistry. Long ago, about 100 years ago, Chemistry and Physics were separate studies. However I am not that old.
    All the reactions you list above also give out heat in the form of photons. Where does the energy come from? E=mc^2. Is this really so difficult? Time to call up your old physics professor.



    Ole.

  14. #14
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    Quote Originally Posted by drsam

    My suspicion is that when you plug your battery into the wall, you are feeding electrons into the negative part of the battery.
    Kind of, but not really. The electrons are already there, voltage is "pressure", an electron won't necessarily travel in a loop, but when a circut is completed, voltage (pressure) is applied and things start moving.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  15. #15
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    Quote Originally Posted by Baconman
    At the speed of light mass is infinite and that's why you can't go any faster.
    Unless you believe in the existence of tachyons.
    Herro prease

  16. #16
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    I'm just amazed this is even being discused.

  17. #17
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    I thought photons....

    ... were massless. That is what allows them to travel at the speed of light. If they had mass, they would go slower than light according to E=mc^2, right?

  18. #18
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    The chemistry of the battery changes

    Quote Originally Posted by drsam
    This is sort of approaching the answer I was expecting, but let me ask you this,

    When the battery is plugged into the wall outlet and charged, exactly what (from the chemistry viewpoint) occurs?
    I'm not sure what the exact chemistry is, but basically, there is a chemical in the battery (like Sulpheric Acid in a lead acid battery) that reacts with the lead plates to change to another chemical as the electrons move from the negative terminal to the positive terminal. Charging the battery changes the acid back to it's original form, more of less (apart from battery wear). Something like that. My electronics teacher (high school, 20 years ago) used to hammer home on us that batteries do not contain energy, they contain chemicals that react and create potential energy.

    Oh, and Sealed Lead Acid batteries don't loose anything.

  19. #19
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    True

    Quote Originally Posted by drsam
    I'm not so sure this is exactly right. Hence my reply asking about exactly what goes on during the charging process in a battery.

    My suspicion, and I'm no expert is that extra stout may be right.

    My suspicion is that when you plug your battery into the wall, you are feeding electrons into the negative part of the battery, which ideed does increase the energy state and the mass of the negative part of the battery, but I suspect that you concomitantly remove an equal number of electrons (and mass) from the positive part of the battery, for a net change in mass of zero.

    I'm not entirely sure about this though.
    You're actually sucking electrons from the positive terminal and stuffing them back in the negative, as in a closed circuit. A battery won't give up any electrons outside of itself, basically. It will give one up if it gets one back.

  20. #20
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    This is a chemical reaction, the acid and lead in the battery remain in the same quantity, therefore there is no loss or gain of mass.

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    Quote Originally Posted by Ole
    All the reactions you list above also give out heat in the form of photons. Where does the energy come from? E=mc^2. Is this really so difficult? Time to call up your old physics professor.



    Ole.
    I don't think E=mc^2 applies here. Chemical reactions rely on the difference in energy of bonds between atoms, not bonds between nuclear particles (protons and neutrons). A chemical reaction that gives off energy goes from a loosely bound molecule to a more tightly bound molecule. Kind of like dropping a mass in a gravitational field.

  22. #22
    Ole
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    Here's some reading.

    Quote Originally Posted by EMeister
    I don't think E=mc^2 applies here. Chemical reactions rely on the difference in energy of bonds between atoms, not bonds between nuclear particles (protons and neutrons). A chemical reaction that gives off energy goes from a loosely bound molecule to a more tightly bound molecule. Kind of like dropping a mass in a gravitational field.
    Why is the energy in energy bonds excluded from E=mc^2? The difference between breaking apart an atom core, and breaking apart two atoms, is that the latter produces A LOT less energy than the former. So you'll also a lot lower mass change, but it's still there.
    After breaking the bond, you still have exactly the same atoms, but with one low frequency photon added, giving heat. This photon gets it's energy according to E=mc^2, and thus reduces the mass of the now un-bonede atoms accordingly.

    Here's a link that explains it. As I first said, it's very small mass, but it's there:
    http://www.newton.dep.anl.gov/askasc.../chem03534.htm

    Photons do have mass, but not in the classical sense: It has zero resting mass, but since it's moving at C, it has relativistic mass:http://math.ucr.edu/home/baez/physic...oton_mass.html



    Ole.
    Last edited by Ole; 10-21-2005 at 03:24 AM.

  23. #23
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    Quote Originally Posted by snaky69
    This is a chemical reaction, the acid and lead in the battery remain in the same quantity, therefore there is no loss or gain of mass.
    Chemical bonds don't just decide to break and rearrange, energy is required to break them and must wind up somewhere. Since mass and energy are one in the same if the battery contains more potential energy then by definition it is more massive as well.

    You probably think things can't be in 2 places at the same time, the cat can't be both alive and dead at the same time, something can't be both a particle and a wave, God doesn't play dice, and how you view an entangled particle won't effect it's brother on the other end of the universe either.

  24. #24
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    Quote Originally Posted by Ole
    Why is the energy in energy bonds excluded from E=mc^2? The difference between breaking apart an atom core, and breaking apart two atoms, is that the latter produces A LOT less energy than the former. So you'll also a lot lower mass change, but it's still there.
    After breaking the bond, you still have exactly the same atoms, but with one low frequency photon added, giving heat. This photon gets it's energy according to E=mc^2, and thus reduces the mass of the now un-bonede atoms accordingly.

    Here's a link that explains it. As I first said, it's very small mass, but it's there:
    http://www.newton.dep.anl.gov/askasc.../chem03534.htm

    Photons do have mass, but not in the classical sense: It has zero resting mass, but since it's moving at C, it has relativistic mass:http://math.ucr.edu/home/baez/physic...oton_mass.html



    Ole.
    Thanks for those links. The first one was very interesting. One person said that all systems that experience a change in energy will experience the addition or subtraction of a small amount of energy, but then several other people said the opposite, that only in nuclear reactions is the mass energy equation valid. So which one am I supposed to take as the truth?

    I am actually believing you are right just because I like that idea more. It's so nicely symmetric.

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