Understanding E=mc^2: Explained in Plain English | Junior's Dilemma

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    E=mc^2
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Discussion Overview

The discussion revolves around the equation E=mc², focusing on its meaning and implications, particularly in relation to energy and mass. Participants explore the equation's significance, its connection to nuclear technology, and the quantitative aspects of energy derived from mass.

Discussion Character

  • Conceptual clarification
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant expresses difficulty in understanding the meaning of E=mc² and requests a plain English explanation.
  • Another participant provides a description of the equation, stating it represents an equivalence between energy and mass, emphasizing that a small amount of mass can yield a large amount of energy, as demonstrated by atomic bombs.
  • A participant questions the relativity of "small" in the context of mass, specifically asking about a 3lb mass.
  • Another participant suggests converting 3lb to kg and calculating the energy using the equation, providing historical context with energy values from the atomic bombs dropped in Japan.
  • Several participants express curiosity about the underlying reasons for the equation, particularly why the speed of light is involved.
  • One participant explains that the energy obtained from mass is proportional to the square of the speed of light, providing a quantitative example of energy derived from 1 kg of mass.
  • Another participant offers a link to a Wikipedia article for further reading on the derivation of the equation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the understanding of the equation, with some expressing confusion and others providing explanations. Multiple viewpoints on the implications and interpretations of E=mc² remain present.

Contextual Notes

Participants mention the need for clarity on the terms used, such as "small" in relation to mass, and the significance of the speed of light in the equation, indicating potential gaps in understanding and assumptions about prior knowledge.

linux kid
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I have read the wikipedia article on this but my mind just can't seem to comprehend the meaning of this equation. I maybe unconsciously thinking too hard...but I'm still junior...

Someone please explain the meaning to me in plain English. :)

PS: BTW, did this equation lead to the discovery of nuclear technology?
 
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I'm not sure what wiki article you read, but here is an easily understood description:

E = mc^2 is an important and well-known equation, which states an equivalence between energy (E) and mass (m), in direct proportion to the square of the speed of light in a vacuum (c2).
http://en.wikipedia.org/wiki/E=mc²

Essentially, this means a small amount of mass, will give us enormous amounts of energy. For example the atomic bomb, which is e = mc^2 in action.
 
ranger said:
I'm not sure what wiki article you read, but here is an easily understood description:

E = mc^2 is an important and well-known equation, which states an equivalence between energy (E) and mass (m), in direct proportion to the square of the speed of light in a vacuum (c2).
http://en.wikipedia.org/wiki/E=mc²

Essentially, this means a small amount of mass, will give us enormous amounts of energy. For example the atomic bomb, which is e = mc^2 in action.

But "small" is a relative term. :confused: What about a 3lb mass?

PS: that is the one I read.
 
You should have all mass in kg. Why don't you try converting 3lb to kg and plug it in the equations and see what numbers you get. To give you can idea of the scale you are dealing with, the atomic bombs dropped in Japan were 63 TJ (Hiroshima) and 84 TJ (Nagasaki), Encyclopedia Americana. And by todays standards, these are small.
 
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I know the equation. I just don't know why/how it works. Why the speed of light?
 
Because that's how much energy you get out of each bit of mass. So if you convert 1 kg of mass (= 2.2 lbs) to energy... you'll get
1 kg * c^2 of energy.

That's 1 kg * (3.0*10^8 m/s)^2 = 9 * 10^16 J of energy, or 9000 TJ. Compare that with those bombs.

To put that into perspective: most humans weigh more than 50 kg.

What e=mc^2 means is that mass is a form of energy and energy is a form of mass. They're different forms of the same thing.

Are you looking for how that equation was obtained? If so, here's the one from the Wikipedia article. I think we did it a simpler way in class, but it's in my pencil-and-paper physics notes.

http://en.wikipedia.org/wiki/E=mc2#Derivation
 

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