# E=mc2

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Is E=mc2 only appied on the earth?

I thought the gravity provide potential energy which is different from other planet.

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it applies everywhre but it depends on where u conduct ur experiment.say on earth if u wanna get a kilogram weighin object all of its potential energy u can have 9x10^16 joules of energy.but take that same object to sun(just assume u can)i believe u could get twenty eight times more energy than u could possibly get on earth.in short it is gravity ,yes.

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Weight doesnt really come into it, as it is gravity dependant and therefore subject to change. Mass on the other hand (as indicated in the formula) remains a constant when stationary, regardless of the pull by gravity

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Weight doesnt really come into it, as it is gravity dependant and therefore subject to change. Mass on the other hand (as indicated in the formula) remains a constant when stationary, regardless of the pull by gravity

Ding ding ding.

Weight =! Mass. Weight is the force caused by mass being acted upon by the force called 'gravity'. For the simple version, F = GmM/d^2 (I can't be having with these crazy 'proper equations'), combined with F = ma. F is the force, G is the Gravitational Constant (gravitational constant = 6.67300 × 10-11 m^3 kg^-1 s^-2, thank you google), m is the object's mass, M is the mass of the big object (the earth in this case) and a is the acceleration, in this case the value 'g' (acc. due to gravity).

F = mg

Therefore mg = GMm/d^2

g = GM/d^2.

This shows the accel due to gravity is independent of the mass of the object, as famously demonstrated by Galileo.

Back to the topic at hand, energy,

Work done = Force x distance

= mgd (height moved x force due to gravity)

= GMm/d.

E = mc^2, on the other hand, has little to do with gravity, and is more of an equivilency when you're changing between 'mass' and 'energy', most usually when you're talking about nuclear binding energy in atomic reactions (well, that's when I've used it the most anyway.)

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That equation works anywhere, gravity has no part it in, just what you see.

Uh, but I think you may be reffering to potential energy from your last sentance or two. If you are, gravitational potential energy is the potential energy something has on planet Earth for example. If an object is suspended in the air, it has potential energy because it can fall.

This equation is E=mgd where E is energy in joules, m is mass, g is acceleration due to gravity and d is distance from the refference point. The refference point would usually be the surface of the Earth, so you could find how much energy something would gain by being dropped to the ground. At sealevel on earth, gravity is 9.8m/s. On other planets this would be different.

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all along i've bn thinkin like mass would not change in a sense that ,we humans for example made of 44% oxygen so that where ever in space we've made of exactly the same amount of oxygen .That's mass. but to get the potential energy from a substance

we mention mass in relation to gravity.as long as we refer mass as kilogram or something in relation to gravity potential energy we derive from them would be dependent of gravity.where i went wrong?

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Well, a kilogram always has a mass of one kilogram, though its weight changes depending on local gravity. When someone weighs themself and says "Oh my god, I weigh XXX kilograms", they're actually measuring weight, but the scale is calibrated for Earth's gravity so it can give a measurement of your mass in kilograms. So weight, being a force, is what changes in gravity, not mass.

E = mc2 doesn't relate to potential energy due to changes in weight though. In this case, E is just the energy in total terms of what's put out during, say, a nuclear reaction (heat, sound, light, kinetic, etc.), and the m is the mass, but not weight. So E = mc2 is basically just a relationship between energy and mass, and since mass is constant regardless of gravity, E = mc2 applies anywhere.

EDIT: My god. I notice over a month later that I wrote "it" instead of "its weight", thereby suggesting that mass changes with gravity (even though I said it didn't lower down). I can't believe nobody laughed at me for that.

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• 1 month later...

$E=mc^2$ only applies to a particle at rest.

If it is moving it should by $E^2=m^2 c^4+p^2c^2$ where the 'p' is momentum. (Setting p=0 gives $E=mc^2$ again.)

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• 1 month later...

E= mc^2 means the following:

A body of mass m is equivalant to energy E or The energy equivalent of a body with mass m is equal to its mass multiplied by a constant (=c^2),where c is the velocity of light.The logical conslusion drawn from this equation is that mass and energy are interconvertible.

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Universal

(Is it a postulate or has it been solved?- I havnt studied it much)

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• 4 weeks later...

Ok, I'm just a stupid Freshman in h.s., so how exactly do you measure mass if it is a constant....how do you measure mass with the reduction of Gravity.....PLEASE HELP ME!!!!!!! I AM AN IDIOT!!!!!!!!!

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I'm not crazy, you're crazy.

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Ok' date=' I'm just a stupid Freshman in h.s., so how exactly do you measure mass if it is a constant....how do you measure mass with the reduction of Gravity.....PLEASE HELP ME!!!!!!! I AM AN IDIOT!!!!!!!!![/i']

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I'm not crazy, you're crazy.

Like say, how would you measure the mass of something in space, not in a noticable gravitational field? I dont really know how they do this now, but you could easily measure it by exerting a force on it and measuring its acceleration, since Force(N)=mass(kg) x acceleration(m/s2).

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Yet in space acceleration is constant without factors like friction, air resistance, and the ever problematic GRAVITY. Besides, on earth we have the theory of gravitation....

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I'm not crazy, you're crazy

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Umm, yes? Because there are so few outside forces such as friction or gravity acting on an object in space acceleration is easy to measure.

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