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Dumb question? E=mc2

Dumb question? E=mc2 - Physics Forum

Dumb question? E=mc2 - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 12-11-2007, 09:31 AM
Andrewr1
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Default Dumb question? E=mc2



How in the hell does this magical formula E=mc2 work with units of measure
that have were previously thought of before the concoction of this formula?
(ie Joules, Kilograms, Kilometers-per-second?) Some miraculous coincidence
of science?


--
"They that can give up essential liberty to obtain a little temporary safety
deserve neither liberty nor safety."
-Benjamin Franklin


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  #2  
Old 12-11-2007, 01:02 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Dumb question? E=mc2

Dear Andrewr1:

"Andrewr1" <[Only registered users see links. ].com> wrote in message
news:475e588c$0$6950$[Only registered users see links. ]...

Imperial units were made in conformity with SI units around 1900,
before the formula was derived.

For what it is worth, like with any other attempts at
thermodynamic measurements in imperial units, you become familiar
with the slug. This energy formula describes "internal energy".

There are good free units converters on the internet...

David A. Smith


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  #3  
Old 12-11-2007, 01:02 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Dumb question? E=mc2

Dear Andrewr1:

"Andrewr1" <[Only registered users see links. ].com> wrote in message
news:475e588c$0$6950$[Only registered users see links. ]...

Imperial units were made in conformity with SI units around 1900,
before the formula was derived.

For what it is worth, like with any other attempts at
thermodynamic measurements in imperial units, you become familiar
with the slug. This energy formula describes "internal energy".

There are good free units converters on the internet...

David A. Smith


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  #4  
Old 12-11-2007, 04:20 PM
Ernie Sty
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Default Dumb question? E=mc2


"PD" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

What I don't understand is, how can you multiply mass by velocity? And how
do you know what units to use?

For example, for mass should I use kilos or pounds? For velocity should I
use miles per second, furlongs per annum, or what? And whatever I should
use, why?


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  #5  
Old 12-11-2007, 04:20 PM
Ernie Sty
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Default Dumb question? E=mc2


"PD" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

What I don't understand is, how can you multiply mass by velocity? And how
do you know what units to use?

For example, for mass should I use kilos or pounds? For velocity should I
use miles per second, furlongs per annum, or what? And whatever I should
use, why?


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  #6  
Old 12-11-2007, 07:38 PM
Ernie Sty
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Default Dumb question? E=mc2


"PD" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

Huh. I've never heard of kinematics and I made it all the way to college.
You must have had a good high school!



So, velocity is a form of energy, right? And inertia, which is kinetic
energy (hmmm... kinetic, kinematics, are they the same?) is mass times
velocity (or mass times something times velocity?)


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  #7  
Old 12-11-2007, 07:38 PM
Ernie Sty
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Default Dumb question? E=mc2


"PD" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

Huh. I've never heard of kinematics and I made it all the way to college.
You must have had a good high school!



So, velocity is a form of energy, right? And inertia, which is kinetic
energy (hmmm... kinetic, kinematics, are they the same?) is mass times
velocity (or mass times something times velocity?)


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  #8  
Old 12-11-2007, 08:59 PM
dlzc
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Default Dumb question? E=mc2

Dear Ernie Sty:

On Dec 11, 9:20 am, "Ernie Sty" <[Only registered users see links. ]> wrote:
....

[Only registered users see links. ]
[Only registered users see links. ]

The units on each side of the equals sign should equate also... just
as if they were x, y, or z unit vectors.

David A. Smith
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  #9  
Old 12-11-2007, 08:59 PM
dlzc
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Default Dumb question? E=mc2

Dear Ernie Sty:

On Dec 11, 9:20 am, "Ernie Sty" <[Only registered users see links. ]> wrote:
....

[Only registered users see links. ]
[Only registered users see links. ]

The units on each side of the equals sign should equate also... just
as if they were x, y, or z unit vectors.

David A. Smith
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  #10  
Old 12-29-2007, 02:08 AM
Tani Jantsang©
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Default Dumb question? E=mc2


"Ernie Sty" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ] ...

1/2 mass times velocity equals momentum. It's just a way to calculate. You
can use whatever units of measurement you want, so long as you are
consistent. You can be 50 make up a word, 50 oooks. Two oooks equal one
pound. That makes you 100 pounds. You still weigh the same, tho.


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