E=mc2

[LeedsRhinos]

I have just read a book explaining the equation E=mc2 (sorry I can't do a smaller 2) I can get my head round the fact that everything contains potentially massive amounts of energy. What I can't get my head round is how it just happens to equate to the mass of the thing times the speed of light squared. Why the speed of light? Why the speed of light squared? Why not the speed of sound squared? Why not the speed of something else Squared or not? TIA

[scotstone]

Kinetic energy is energy which a moving object possesses.
The amount of energy it has depends on :-

a) its mass. ie the more massive it is the more energy it will have. In fact the amount of energy is directly proportional to its mass. Double the mass and the amount of energy it has will be doubled etc.

b) its velocity. ie the faster it is moving the more energy it will have. However the amount of energy is directly proportional to its speed squared. It can be shown experimently and by other means that if the speed is doubled then the energy increases by a factor of four (two squared) or if the speed is trebled then by a factor of nine (three squared) etc

Using experimentation and proportionality maths it can therefore be shown that.

Kinetic energy = mass x velocity^2/ 2 where the 2 is the coefficient of proportionality.

ie. E = mv^2/ 2

E= mc^2 is just a variation of this formula where physicists like Einstein have shown that the energy possessed by all mass is dependent on its mass and and that the velocity happens to be the speed at which light travels. This speed is used because as this speed is approached mass and energy become interchangeable.

This is a simplified explanation but to understand it fully requires a doctorate in theoretical physics I would think but it should explain why mass and speed of light squared are involved.

[brachiopod]

Nice answer, scotstone.

[Quizmonster]

To get the small '2' meaning 'squared', hold down the Alt key and type 253 on the numeric keypad on the right of your keyboard...so mc�.

[chakka35]

Many thanks Quizmonster. I have found all sorts of useful symbols by pressing Alt and various combinations of numbers on the numeric keypad.
Any idea how I can get the symbol for 'half'' ? 1/2 never looks right. Annoying that it's not on the my computer keyboard when it has been on every typewriter keyboard I have ever used.

[tony1941]

� or even � or �. These are, respectively: ALT plus:
0188
0189
0190

I have a little executable file called "keypad" which shows the whole font and gives you the "alt plus" code when you hover over the character. Google GSP and look for the software outfit in Guildford. Very Useful.!!!!

[chakka35]

Many thanks, tony1941.