Question about e=mc2

[ridgey]

In the famous equation, how is c the velocity of light expressed?

How do you express velocity, without a refrence to distance or time?

[NeonBlack]

Short answer: C is invariant.

This basically means that the speed of light is the same in all reference frames.

[ridgey]

ok, But what is the number?

how do we express velocity?

[insane_alien]

C=~300000000m/s

[ridgey]

Thanks. The next question is, how do we express m (mass)

is it just in grams?

[NeonBlack]

velocity in meters per second and mass in kilograms gives you energy in joules.

[ridgey]

thank you very much

[ridgey]

Is this correct?

the amount of energy contained in 1kg of matter 1*(300000000*300000000)=90000000000000000joules.

[Severian]

Yes. It would be nice to write 9x10¹⁶J though.

[ydoaPs]

it's not completely right...momentum...

[Dave]

I think we can safely assume that the block is stationary in this case.

[ydoaPs]

stationary relative to what?

[ydoaPs]

[math]E^2=(mc^2)^2+({\rho}c)^2[/math]

[Kniteli]

Now how to tap to tap all that energy, oh the wonders..

[ydoaPs]

fission, fusion, matter/antimatter anhialation

[insane_alien]

pogos just imagine that the block is in a universe all by its self and is stationary relative to the universe(assume its a universe where you canfind the centre easily)

[danny8522003]

Is this correct?

the amount of energy contained in 1kg of matter 1*(300000000*300000000)=90000000000000000joules.

 

In nuclear weapons, only a very very tiny amount of the actual material used in the bomb is converted to energy. Im not sure of the exact figure but i think it was only a few grams.

[JSKrimmel]

In nuclear weapons, only a very very tiny amount of the actual material used in the bomb is converted to energy. Im not sure of the exact figure but i think it was only a few grams.

 

I did some rough calculations and using estimates of energy yields, determined approximately the amount of mass that was converted into energy for both the Little Boy dropped on Hiroshima and the Fat Man dropped on Nagasaki.

The Little Boy was composed of uranium-235 and although the critical mass, or the mass needed to sustain a chain reaction, for U-235 is 50 kg, only approximately 0.6043 grams were converted to energy.

The Fat Man, made of plutonium-239, had a critical mass of only 10 kg yet only between 0.9297 and 1.162 grams of plutonium were actually converted to energy.

[danny8522003]

Ah i remember now - that sounds about right.

 

That's not a lot of mass considering the size of the explosions :\

[JSKrimmel]

Living in a world so advanced in technology and so overwhelmed with conflict makes those numbers seem even smaller.

 

An extension of the calculations above using rather conservative death toll estimates shows that on the average it took only 7.470 micrograms (10^-6 g) to kill a single person in Nagasaki and just 4.316 micrograms per individual with the more efficient uranium bomb dropped on Hiroshima. (To put it in perspective, each fragment of a paperclip cut into one million pieces would weigh one microgram.) One can only imagine what 60 years of scientific advancement has done to those figures.

[swansont]

Living in a world so advanced in technology and so overwhelmed with conflict makes those numbers seem even smaller.

 

An extension of the calculations above using rather conservative death toll estimates shows that on the average it took only 7.470 micrograms (10^-6 g) to kill a single person in Nagasaki and just 4.316 micrograms per individual with the more efficient uranium bomb dropped on Hiroshima. (To put it in perspective' date=' each fragment of a paperclip cut into one million pieces would weigh one microgram.) One can only imagine what 60 years of scientific advancement has done to those figures.[/quote']

 

60 years of scientific advancement hasn't changed the speed of light...

[danny8522003]

Lol i think he means the amount of mass used up in the explosions. It's efficiency i think.

[swansont]

Lol i think he means the amount of mass used up in the explosions. It's efficiency i think.

 

The efficiency of how much energy you get from a set amount of mass is given by c²

 

OTOH, you could become more efficient by converting a higher fraction of the bomb's mass to energy, but those relevant numbers aren't the ones that were quoted, as far as I can tell.

[JSKrimmel]

Naturally I meant that the mass converted into energy would be increased by 60 years of scientific advancement.

 

For example, I know that separating U-235 isotopes was a major challenge. 60 years of advancement would allow for more pure samples of U-235 to be separated, potentially making a more destructive bomb by increasing the amount of mass converted to energy.

 

Also, a bound on the size of the atomic bomb was the weight allowance of the airplane used to transport it. Today's larger bombers obviously have larger payloads and would be able carry approximately 3 times more weight than the Enola Gay. A bigger bomb would allow for more mass to be converted to energy, making the bomb deadlier still.

 

The point that I was trying to make is that there are many scenarios we can come up with that would allow for more mass to be converted to energy. I apologize for not being more explicit.

[jcarlson]

You forgot to mention the ICBMs on Subs... each sub can hold up to 24 ballistic missiles with up to 10 warheads on each, with each warhead capable of leveling a city.

 

Did you know that if a SSBN was its own country, it would be the third largest nuclear power in the world? (after the US and Russia)