On Saturday, November 12, 2005 at 1:00:33 PM UTC-7, Doink wrote:
OK, Energy = Mass X Speed of Light Sq.
I understand the principle, that this translates to a BIG number and thus a lot of energy is contained in matter. Yes, matter is essentially frozen energy. Stipulated.
By I'm thrown by the SPEED of light thing. If something has a mass of 10 grams and I multiply it by 386,000 mph it doesn't make sense. Is there a scientific conversion from speed to some other unit????? How do you
multiply mass times speed? Or is it just representational? Can the explanation be simplified?
E = mc^2 is indeed consistent from the point of view of the use of units.
One unit of energy is the foot pound. That is the amount of energy you
use to lift an object that weighs a pound by a foot.
However, that is not a unit of energy if you consider the pound to be a
unit of mass. The pound is being lifted against the force of gravity, which
is implied - unless you instead use the pound as a unit of force.
So in the metric system, the basic unit of energy, the Watt, is equal to
one Newton - metre. The work required to move something one metre,
against an opposing force of one Newton.
And what other units can be used to express a Newton?
A Newton is the force which, when acting on a mass of one kilogram
(not a gram, as the SI is basically a slight modification of the MKS
system of units, where the metre, the kilogram, and the second are
fundamental; the other old metric system was CGS, where the
centimetre, the gram, and the second were fundamental; in that system,
the unit of force is the dyne, and 100,000 dynes make a Newton) will
cause its motion to accelerate at the constant rate of one metre per
second... per second. So after a second, its velocity increases by
one metre per second.
So one Newton is one kilogram times one metre divided by one second
squared. Therefore, one Watt, which is a Newton-metre, is one kilogram
times one metre squared divided by one second squared.
Therefore, energy is measured in units that are equivalent to mass
times velocity (one metre divided by one second) squared. E = mc^2,
therfore, is dimensionally correct.
John Savard
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