question about mass-energy equivalence

[dragonstar57]

E=mc^2

where

E=energy

M=mass

c= the sped of light

so the equation is really

E=M*C^2

and sense we know what C is why do we put it to the second when we can just figure out what C^2 is and make that the constant?

why not just put the value in the equation from the start?

[Mr Skeptic]

Three reasons:

1) From a theoretical aspect, the equation is more meaningful this way

2) There's no need to make new constants to keep track of and have to measure independently.

3) If anyone wants to do a lot of these calculations they can easily make the substitution you suggested.

[ajb]

I expect if you put the numerical value in for the speed of light from the start then its significance would quickly get lost.

 

The same goes for Planck's constant, Newton's constant, the electron charge etc...

[swansont]

E=mc^2

where

E=energy

M=mass

c= the sped of light

so the equation is really

E=M*C^2

and sense we know what C is why do we put it to the second when we can just figure out what C^2 is and make that the constant?

why not just put the value in the equation from the start?

 

In practice, we do use c^2 as a constant: ~931.5 MeV/amu

[netrat]

In physics we find building blocks of universe. Building blocks are called Fundamentals. Fundamentals are entities which either are never-changing constants or which cannot be broken down any further.

Speed of light © is fundamental just like length(L) and time (t).

c appears in many equations.

c is manipulated in many equations by multiplying, dividing, adding, subtracting other values to it.

in case of E=MC^2

 

C is manipulated just by putting the power of 2. But fundamental still remains C.

 

But U are not restricted, U can make C^2 as constant. Only the simplicity of equation (also called beauty) will turn into complexity by introduction of new constant because now you have to remember another constant, and physicists love to use as less brain as possible:lol:.

[dragonstar57]

I don't mean another constant i just mean using the value of c^2 rather than figuring it out EVERY time you use the equation!

[losfomot]

I don't mean another constant i just mean using the value of c^2 rather than figuring it out EVERY time you use the equation!

If you are doing these types of equations frequently, then you will probably have a good calculator. Good calculators have letters that you can assign value to. I imagine most physicists have the value of c assigned to the letter c on their calculator. It is much easier to punch c^2 into your calculator than to figure it all out ahead of time and punch the actual long number in.

[dragonstar57]

oh.. I get in now!

[swansont]

If you are doing these types of equations frequently, then you will probably have a good calculator. Good calculators have letters that you can assign value to. I imagine most physicists have the value of c assigned to the letter c on their calculator. It is much easier to punch c^2 into your calculator than to figure it all out ahead of time and punch the actual long number in.

 

I type in 3e8 for c, and 931.5 for c^2.

[Mr Skeptic]

Or if you put it into Google Calculator, it will know the value of c and of c^2.

[dragonstar57]

anyway to make Google to the whole equation?

and the mass and energy in E=mc^2 what units do they use?

is the mass measured in grams and the energy measured in newtons ?

and how do you multiply by 8.98755179 × 1016 m^2 / s^2?

Edited September 4, 2010 by cipher510

[Mr Skeptic]

You can use any of the correct units. Newton is a unit of force, not of energy. For mass you can use stones, pounds-mass, grams, kg, ounces, etc. For energy you can use Joules, ergs, foot-pound, etc. Some units Google calculator does not know, but many it does.

 

Eg like so:

http://www.google.com/#hl=en&source=hp&q=1+kg+*+c^2&aq=f&aqi=&aql=&oq=&gs_rfai=CGN-YKYCCTMW4Iae-zgSht9GLBQAAAKoEBU_QkE0w&fp=e2c546720953fc59

or

http://www.google.com/#hl=en&q=1+stone+*+c^2&aq=f&aqi=h1&aql=&oq=1+stone+*+c^2&gs_rfai=&fp=e2c546720953fc59

And for great fun:

http://www.google.com/#hl=en&q=c+in+furlongs+per+fortnight&aq=1&aqi=h1g1&aql=&oq=c+in+furlong&gs_rfai=&fp=e2c546720953fc59

[dragonstar57]

so if 4 million lbs on matter were annihilated how much energy would be released?

(in megatons)

[Mr Skeptic]

Calculate it with E=mc^2, and then convert to megatons TNT.

[swansont]

anyway to make Google to the whole equation?

and the mass and energy in E=mc^2 what units do they use?

is the mass measured in grams and the energy measured in newtons ?

 

Energy in in Joules or electron-Volts. Most calculations using E=mc^2 will use the latter, and the mass will be in atomic mass units (where C-12 has a mass of exactly 12)

 

and how do you multiply by 8.98755179 × 1016 m^2 / s^2?

*

9

Exponent

16

= (or next function)

 

Assuming you aren't using a calculator that uses RPN.

[vuquta]

What value should we use with the earth's rotational sagnac since it is not provably not c.

 

In fact, under that context, how would we interpret energy since by GPS it is direction based.

[swansont]

What value should we use with the earth's rotational sagnac since it is not provably not c.

 

In fact, under that context, how would we interpret energy since by GPS it is direction based.

 

!

Moderator Note

What does this have to do with mass-energy equivalence? Do not hijack threads.