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Author Topic: Would my weight change if I ate a burger while standing on some scales?  (Read 4540 times)

Abbas Dhanani

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Abbas Dhanani  asked the Naked Scientists:

If I stood on weighing scales while holding a big juicy burger. Would my total weight change if I ate the burger? I always thought I'd get lighter but I can't reason why.

What do you think?
« Last Edit: 16/06/2015 17:04:23 by Georgia »


 

Offline Supercryptid

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The scale would measure your weight as the same both before and after you ate the burger. The scale doesn't care whether the burger is in your stomach or in your hand; you weigh the same when added together either way.
 

Offline faxof

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Hey

Thanks for replying, but what about longer term?

Will I stay the same weight for the whole period of time between eating the burger and 'voiding' the burger?

i.e. does the chemical breakdown effect weight?

-Abb
 

Offline Supercryptid

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For dieting purposes, no, chemical breakdowns don't change the weight of the chemicals in question. A hamburger takes several forms after being digested: carbon dioxide gas which is exhaled from the lungs, fat that is stored in the body, liquid and solid waste, plus perhaps other things like sweat. Add the weights of all of these things together and you will get the same weight as the original burger (plus the oxygen used to "burn" the calories in it).
 

Offline thedoc

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Hear the answer to this question on our show
« Reply #4 on: 16/06/2015 16:00:39 »
We discussed this question on our  show
Chris - I would argue that, actually, the burger is already mass in your hand on the scales and therefore, if you put it into your mouth, it just turns into mass in your body.
There would then be some metabolism, obviously, because youíve got to exert some energy to work the muscles of mastication to chew up the burger. And to produce some saliva; youíve got to warm your body which means you're burning some energy doing that as well and you presume the burger is going to be a bit lower than body temperature probably by the time youíve done your experiment.
So there's a little bit of a loss of energy there. So, that means you're going to lose a little bit of mass. Metabolism thatís going to carry on as you digest the burger as well, because you got to break it down into its component parts and absorb it. I reckon in the short term, no change. In the long term, thereíd be a modest small reduction in mass...
Max - How accurate your bathroom scale is?
Chris - Well, that was going to be my bottom line, if you excuse the pun, because I was going to say that actually, you're talking about trivialities. Once the burger goes in, the burger becomes part of you. There will be some losses to the toilet though and so, a certain amount will be absorbed and a certain amount won't be absorbed. And so, you won't get all of the energy turning into mass. But letís assume that none of the burger is wasted. It would all get converted either instantly into sugars that you would burn or fat that you would store, so your body mass would reflect the increase in weight gain owing to the burger...
Click to visit the show page for the podcast in which this question is answered. Alternatively, listen to the answer now or [download as MP3]
« Last Edit: 01/01/1970 01:00:00 by _system »
 

Offline Maizie

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I swear my stomach and thighs get bigger by every bite!
 

Offline PmbPhy

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I swear my stomach and thighs get bigger by every bite!
I don't understand this. I tried quoting some of the posts above and it gave me a message saying
Quote
An Error Has Occurred!
 
The post you are trying to quote either does not exist, was deleted, or is no longer viewable by you.

When you eat, the matter breaks down in the process which means that chemical bonds are broken. During this process energy is converted to heat and that heat is radiated out of the body in various forms thus decreasing the mass of your body. However if we don't get that precise then in all chemical processes mass is conserved so that your bodies mass won't change unless you perspire or your body expels waste.
 

Offline alancalverd

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Quote
So there's a little bit of a loss of energy there. So, that means you're going to lose a little bit of mass.

I think not. Digestion is not a nuclear reaction! You are converting the potential energy of e.g. sugar bonds, into kinetic energy. No nuclei are transformed by

3nO2 + 2(CH2)n → 2nCO2 + 2nH2O + heat

so the final mass is the same as the starting mass plus the mass of oxygen you inhaled to oxidise your food.

Were it not so, the universe would have disappeared into a burst of photons a long time ago.
« Last Edit: 25/06/2015 08:05:54 by alancalverd »
 

Offline PmbPhy

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Quote from: alancalverd
I think not.
Ummm. I think so.

Quote from: alancalverd
Digestion is not a nuclear reaction!
Obviously. But so what? You don't really think that E = mc2 only applies to nuclear reactions, did you?

Quote from: alancalverd
You are converting the potential energy of e.g. sugar bonds, into kinetic energy.
That's right. And as I said above
Quote from: PmbPhy
During this process energy is converted to heat and that heat is radiated out of the body in various forms thus decreasing the mass of your body.
I should have said that During this process the potential energy in chemical bonds is converted to kinetic energy which manifests itself as heat. etc

Quote from: PmbPhy
No nuclei are transformed by

3nO2 + 2(CH2)n → 2nCO2 + 2nH2O + heat
Again, so what? Why do you keep talking about nuclei? The reason that energy is released in nuclear transformations is because the potential energy in the nucleus from the strong force and the electric force is converted into the kinetic energy of the daughter nuclei and that's where nuclear energy comes from. In the case of digestion, if your equation is right (I don't know about the chemical processes in digestion) then there is potential energy in the chemical bonds of the sugars. That change in potential energy ends up being a change in the mass of the molecules.

Quote from: PmbPhy
so the final mass is the same as the starting mass plus the mass of oxygen you inhaled to oxidise your food.
Wrong. Again, you're confused. For some strange reason you don't know that mass changes in nuclear transformations happen for the exact same reason as mass changes in molecules. In the case of the former the potential energy is in the nuclear bonds between nuclei and the later the potential energy is in chemical bonds. The later is simply and insignificantly smaller than the former.

Quote from: PmbPhy
Were it not so, the universe would have disappeared into a burst of photons a long time ago.
Not at all. The energy released in nuclear reactions is not just in the form of photons. It's also in the form of kinetic energy.

Again, I'm extremely surprised that you didn't know this. It's very small though. To see this go to:
https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence
Quote
The more common association of mass–energy equivalence with nuclear processes derives from the fact that the large amounts of energy released in such reactions may exhibit enough mass that the mass loss (which is called the mass defect) may be measured, when the released energy (and its mass) have been removed from the system; while the energy released in chemical processes is smaller by roughly six orders of magnitude, and so the resulting mass defect is much more difficult to measure.
See? There is energy released in chemical processes. It's six orders of magnitude smaller, but it's there.

I'm beginning to think that you didn't know that the energy released in chemical reactions!? That's not true. Tell me that's not true!!  [xx(]
« Last Edit: 25/06/2015 14:57:57 by PmbPhy »
 

Offline David Cooper

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You are losing weight all the time (ignoring the mass of air being breathed in and out which causes fluctuations up and down if you include it), but if you eat the burger you will lose weight a bit faster as you munch and swallow it, even before you start digesting it. Some of the energy will be lost as sound and other vibrations (in addition to heat), but all of that lost energy starts as energy released from the rearrangement of bonds between atoms where a process similar to combustion is going on.
 

Offline PmbPhy

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Quote from: David Cooper
You are losing weight all the time (ignoring the mass of air being breathed in and out which causes fluctuations up and down if you include it), but if you eat the burger you will lose weight a bit faster as you munch and swallow it, even before you start digesting it. Some of the energy will be lost as sound and other vibrations (in addition to heat), but all of that lost energy starts as energy released from the rearrangement of bonds between atoms where a process similar to combustion is going on.
 

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