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Energy Formula

Date: 10/02/2002 at 09:48:52
From: Jordan Bates
Subject: Energy formula

What does e=mc^2 mean, and why?

Date: 10/02/2002 at 11:27:38
From: Doctor Ian
Subject: Re: Energy formula

Hi Jordan,

It means that mass can be converted to energy, and vice versa. 

It helps to look at the dimensions on the right side of the equation:

  energy = mass * (length/time)^2

         = (mass * length/time^2) * length

         = (mass * acceleration) * length

         = force * length

And this is how energy is defined. 

A practical application of the formula would be in describing what 
happens in a nuclear reactor. In such a reactor, you start with atoms 
of fissionable uranium, and you bombard them with neutrons, in order 
to break them apart - sort of like throwing rocks at light bulbs. 

When you break apart a uranium atom, the protons and neutrons 
re-organize themselves into smaller atoms (and some of the neutrons 
fly off to hit other uranium atoms, which is what keeps the reaction 
going). But if you add up the masses of all the parts, it turns out 
that the sum is less than the mass of the original uranium atom!  

What happened to the missing mass? It's not missing at all - it's just 
been converted to heat. How much heat?  To compute the amount, you use 
the equation e = mc^2. 

Does this help?

- Doctor Ian, The Math Forum 
Associated Topics:
High School Physics/Chemistry

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