Explain E = MC2

USArmyParatrooper
Science 11 Mar '10 16:32
1. 11 Mar '10 16:32
I was wondering if someone can explain this theory and tie it into the formula.... in layman's terms.
2. AThousandYoung
West Coast Rioter
11 Mar '10 17:041 edit
Originally posted by USArmyParatrooper
I was wondering if someone can explain this theory and tie it into the formula.... in layman's terms.
Atoms are made of protons, neutrons, and electrons. The protons are positively charged, yet they are all stuck together very close. The electrical repulsion is very powerful.

When you ping the nucleus with a neutron, it breaks up that stability (if the nucleus is larger than iron's) and you get a nuclear fission reaction.

Now, if you measure the mass of the pieces that are left of the nucleus and compare them to the nucleus before it was broken up, you will find some mass has "disappeared" and more energy is released than expected than one would expect from simply the elecrical repulsion between protons.

One can calculate how much more energy is "created" if one knows how much mass is "missing" via that formula (though that formula assumes there's no motion, it's a little bit longer than that if the object is moving).
Baby Gauss
11 Mar '10 17:36
Originally posted by USArmyParatrooper
I was wondering if someone can explain this theory and tie it into the formula.... in layman's terms.
look out in this forum because I'll bump this thread with what I hope to be an answer to your question.

In the meantime here's an excellent not so layman's explanation to E=mc^2:
http://terrytao.wordpress.com/2007/12/28/einsteins-derivation-of-emc2/
4. 11 Mar '10 19:52
In laymen's terms, you can make mass "disappear" by turning it into energy. Vice versa you can turn energy into mass. The c² determines how much mass you get from a certain amount of energy and vice versa - e.g. if you turn 1 kg of mass into energy you get 1 kg * (3*10^8)^2 m²/s² = 9*10^16 J of energy.
5. 11 Mar '10 19:59
E = mc² is not really a "theory" however, it's just an equation, which can be derived from special relativity theory.

Relativity theory is pretty simple, conceptually. It means two things:

1. For all observers, the speed of light is the same, c.
2. In all intertial frames of reference (i.e. an observer who is not accelerating), the laws of nature are the same.
6. AThousandYoung
West Coast Rioter
11 Mar '10 21:32
Originally posted by KazetNagorra
In laymen's terms, you can make mass "disappear" by turning it into energy. Vice versa you can turn energy into mass. The c² determines how much mass you get from a certain amount of energy and vice versa - e.g. if you turn 1 kg of mass into energy you get 1 kg * (3*10^8)^2 m²/s² = 9*10^16 J of energy.
That's oversimplified. You can only do this under very specific circumstances in a very limited way. You can't use a chair to recharge your car battery!
7. 12 Mar '10 09:56
Originally posted by AThousandYoung
That's oversimplified. You can only do this under very specific circumstances in a very limited way. You can't use a chair to recharge your car battery!
Sadly, the laymen's explanation is always oversimplified. But it will suffice to say that there are certain conditions under which it works.
8. AThousandYoung
West Coast Rioter
12 Mar '10 14:442 edits
Originally posted by KazetNagorra
Sadly, the laymen's explanation is always oversimplified. But it will suffice to say that there are certain conditions under which it works.
I don't think my less simplified version is too hard for the layman. I think yours however tends to lead laymen to false understanding.

I often see people quoting journalists who oversimplify scientific ideas until they're so simple they are actually no longer correct. I think this is a poor idea.

Your assertion that mass can be changed into energy is a bit misleading to the layman I think.

Our audience is an intelligent military man. He probably knows what a proton and a nucleus are, and he's familiar with the concept of nuclear fission I imagine.
9. 12 Mar '10 20:07
Originally posted by AThousandYoung
That's oversimplified. You can only do this under very specific circumstances in a very limited way. You can't use a chair to recharge your car battery!
You could if you had an anti chair!
10. AThousandYoung
West Coast Rioter
14 Mar '10 00:579 edits
I may have misspoken about the nuclear energy being "more than" the electric repulsion of protons.

All I know for sure is that the only time you can really use this formula that I know of is calculating how much energy you will get when you break up a large atom in nuclear fission. You do this by carefully measuring masses of the uranium atom's nucleus (or plutonium etc) and those of the two atoms is breaks up into. There will be some mass missing; the two small nuclei added together don't make up the total mass of the uranium atom. Using E = mc^2 the energy released from this reaction can be predicted by the change in mass.

The reason this is only useful for nuclear reactions is that so much energy is released that you can actually measure the mass difference. Any time you put energy into something (stretch a rubber band, wind up a clock) you increase it's mass proportionally to it's energy by that formula but only by an unmeasurable, tiny, tiny amount. You can only measure it in nuclear reactions but there is a mass change any time energy is stored or released in an object.

Oh, also - if matter meets antimatter, the mass disappears and energy is released as per that formula.
11. sonhouse
Fast and Curious
15 Mar '10 00:36
Originally posted by KazetNagorra
In laymen's terms, you can make mass "disappear" by turning it into energy. Vice versa you can turn energy into mass. The c² determines how much mass you get from a certain amount of energy and vice versa - e.g. if you turn 1 kg of mass into energy you get 1 kg * (3*10^8)^2 m²/s² = 9*10^16 J of energy.
That last # is in Joules, a unit of energy. One joule spread out over one second is one watt-second, that # is almost 1 with 17 zeros behind it, (0.9 with 16 zeros actually but close enough for government work) so one Kg (2.2 pounds) can power a 100 watt light bulb for 30 million years I believe is the usual way of putting it. Also that means that you could have 30 million watts going continuously for 100 years or 300 million watts for 10 years or 3 billion watts for 1 year. If you actually are generating 3 billion watts (3 gigawatts) you run out of your 1 kg fuel in one year. So the US generates about 3000 billion watts, 3 odd Terawatts, so if you were converting mass to energy with 100 percent efficiency you would use 1,000 Kg of fuel per year for the whole USA, about one ton per year for everyone in the US, that is a far cry from the millions of tons now used to get that same amount of energy from burning stuff.
12. 15 Mar '10 04:59
why does the speed of light turn up in this formula?
13. 15 Mar '10 05:13
It's merely a conversion factor. You could work in the so called "natural units" where E=m.
14. 15 Mar '10 10:07
Originally posted by sonhouse
That last # is in Joules, a unit of energy. One joule spread out over one second is one watt-second, that # is almost 1 with 17 zeros behind it, (0.9 with 16 zeros actually but close enough for government work) so one Kg (2.2 pounds) can power a 100 watt light bulb for 30 million years I believe is the usual way of putting it. Also that means that you could ...[text shortened]... far cry from the millions of tons now used to get that same amount of energy from burning stuff.
Well, if you look at nuclear plants they have a pretty decent efficiency, about 20% or so, and it works by the same principle.
15. 15 Mar '10 11:49
Originally posted by KazetNagorra
Well, if you look at nuclear plants they have a pretty decent efficiency, about 20% or so, and it works by the same principle.
I think you're using different ideas about efficiency here. If nuclear power stations have 20% efficiency, that will mean that 20% of the energy released from the atoms is output as electrical energy. There's no way, though, that they are converting 20% of the mass into energy.