> Mass cannot be converted to energy except through nuclear reactions
This is wrong enough to make me stop reading.
This is wrong enough to make me stop reading.
EDIT/replying:
I'm inclined to continue to believe that it can't in any other way.
1. Not through a chemical reaction; energy can be released in a chemical reaction, but the total mass/atoms involved remains the same.
2. Not through kinetics; energy can be produced, but mass remains the same as well.
cf. some interesting caveats here http://en.wikipedia.org/wiki/Conservation_of_mass
Q is the released energy. If you weigh the molecules before and after very carefully, you will notice that they lose weight (or mass if you are being pedantic about it). That mass loss corresponds exactly to the Q-value (through E=mc²).
Any mass gained or lost will be due to changes in bond energies, and the corresponding emission or absorption of photons that change the energy states of the electrons in the bonds.
If you measure the mass of a quantity of water accurately enough, the mass will be lower than the mass of the equivalent amount of hydrogen and oxygen gas. The difference would be so small that our most sensitive instruments would not be able to detect it.
Likewise, in a nuclear reaction, the only thing changing is the nuclear binding energies of the protons and neutrons. However, since the energy involved is many orders of magnitude higher, our instruments are sensitive enough to detect the difference in mass.
If you walk up a flight of stairs, you will be heavier at the top. If an electron changes orbital, its mass changes as well, making it heavier or lighter.
Let's calculate it. A 90 kilogram man walks up a flight of stairs, one story (3.3 meters). The expression "m * g * h" gives us the gravitational potential energy of mass "m" ascending height "h". Evaluating the formula we get 2910 joules. So how much heavier has the man become? Given E=mc^2, then m = E/c^2. As you can see, we'll be dividing by c^2, which is a very big number. The resulting increase of mass is 3.24 E-14 kg, or too small to be noticeable, but still very real: A 90 kg man ascending a 3.3 meters gains 0.00000000000003 kilograms of mass.
Chemical potential energy changes result in mass changes as well. These changes in mass are insignificant at the scale of chemical reasons, but are indeed taking place. So while it may be reasonable to simplify a discussion of chemistry by saying that chemical reactions don't change mass, in reality the changes do take place, just at a very small scale. A starting point for further research:
"Whenever any type of energy is removed from a system, the mass associated with the energy is also removed, and the system therefore loses mass. This mass defect in the system may be simply calculated as Δm = ΔE/c^2"
https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalenc...
Someone else can calculate the decreased buoyancy in thinner air ;)
Edit: Notice I put mass in quotation marks. I am not trying to break the law of conservation of mass. Fat cells consumed will produce energy through some kind of biological process.
This is only approximately true. It would be hard to measure the difference, for sure. Relativity gives a lot of seemingly bizarre results:
* If you carry something uphill, it gains mass as you go. (Kind of... consider that it is part of a system which includes the Earth.)
* If you compress a spring, it gains mass.
* If you charge a battery, it gains mass.
* If you fire a laser into space, it will have a longer wavelength when it gets there.
* If you hook a shaft from the ground into space and turn it, it will turn faster at the bottom and slower at the top.
We live in the "middle ground" which is well approximated by Newton's laws. Strictly speaking, Newton's laws are false.
Does a block at rest sitting on the top of a hill have more mass than a spinning block at the bottom of a hill (assuming the rotational kinetic energy equals the difference in potential energy)?
Since the energy can end up anywhere and the energy has mass, the mass can end up anywhere, too.
If you take a block of steel from the top of a hill to the bottom of the hill and convert all the potential energy to kinetic energy (without loss), why would the mass of the block be altered? It may well be true, but arguments based on applying the mass-energy equivalence is not the answer.
Likewise, if you start with some pool of molecules and rearrange the constituent atoms and bonds, energy must be balanced via kinetics (i.e. translational and rotational energy of and within molecules on both sides of the reaction)--why should anyone expect the overall mass to change from such chemical reactions?
Note: this amount of mass is very small and so is typically left out of introductory chemistry courses.
For example, a person consumes approximately 2000 kcal/day of food. The calculation is more complicated, because not all the energy is used. But for the sake of the argument, let's assume that the person just use all the 2000 kcal and they are lost as heat, work (lifting a heavy object , moving the air, moving the water while swimming, ... )
Using the famous E=mc^2 equation we have that m=2000 kcal/c^2 = 9E-8 grams = 3E-9 ounces. That's very small and is not useful for a diet, but it's not zero.
That's the kind of thing that might make people want to stop reading.
Example:
You have some fissible material that undergoes a nuclear reaction in a closed system and the reactants turn into products with lower mass.
The mass of the system doesn't actually go down until/unless the system cools down.
edit: The above commenter is still being pedantic though
Yes, it's quite true that in physics, mass cannot be turned into to energy. But the article's not talking about physics; it's talking about biology, and in biology, fat can be turned into energy --- that's why your body makes it.
Yes, of course it's not a nuclear process. The fat's metabolised into energy and waste products, which are excreted mostly through the lungs. Also via the skin, urine, faeces and any other bodily fluid --- one byproduct is water.
'It's turned into energy' is actually the right answer if you're thinking about biology. It's just not a complete one. The article would have done much better to have instead said 'you're right, but' and then gone on to explain, rather than just saying 'if you think this you suck'.
The picture changes when you're down to those last few pounds. To get those off, you have to keep up the reduced caloric intake, and you also have to exercise. If you slack off on the former, you'll gain weight back. If you don't exercise, you won't lose any fat.
Building habits and willpower is a journey that takes at least a year and involves changing your relationship with food. To a large extent, we see food as entertainment, it takes a long time before our subconscious minds' adjust to thinking about it as fuel. Inherent in this is replacing that hole left in our psyches where food entertainment used to be with something else as entertainment.
It was a whole year after I started dieting before I started looking at salads as a perfectly acceptable lunch, perfect for getting a feeling of fullness without blowing up the calorie meter. For a long time I played this game of trying to get the most value out of my calorie budget, still mind thinking of food as entertainment.
I did intermittent fasting, which was effective at helping me lose weight but not at keeping it off because it didn't solve the food-as-entertainment issue. Once I got down to a more reasonable weight I stopped, and before I knew it I was fat again, though not nearly as fat as before. I hadn't stopped thinking of food as something to cure boredom with.
I eat better than I ever have, and look more youthful at 31 than through most of my twenties. Ironically, I feel I also enjoy food a lot more than I used to. I taste it better, I find it more interesting. In a Buddhist non-attachment sort of way.