Nomomo wrote: ↑Sun Nov 14, 2021 5:48 am
MeDotOrg wrote: ↑Sun Nov 14, 2021 3:16 am
A miscellaneous fact I always found fascinating:
We all know E=MC2, but what we get from that is there is a tremendous amount of energy in matter, but in practical terms what does it mean?
For the atomic bomb exploded over Nagasaki, scientists estimate that the amount of matter converted into energy was ONE GRAM, about 1/3rd of a penny.
A third of of a penny - Amazing! I was unaware the scale was that minusical.
It's not so difficult, if you use that standard scientific system of units, in which E is in joules, m is in kilograms, and c is in metres/second, and all the numbers work out consistently with no awkward conversion factors.
The c in that equation is the speed of electromagnet waves (which includes light) in a vacuum, 300,000,000 metres per second.
The mass m is 1 gram, which is 1/1000 kilogram.
c squared just means c multiplied by itself, c x c, which is 90,000,000,000,000,000 (metre/second squared). Multiply that by the mass, 1/1000 kilogram, and you get 90,000,000,000,000 joules of energy.
How much energy is that?
Well a 1 kilowatt device, such as a small radiant electric heater, uses 1000 Joules every second. 90,000,000,000,000 Joules of energy would run 90,000,000,000 such heaters for a second. That's 90 billion electric heaters focussed on Hiroshima for a second. Quite enough to vaporise it.
The reason the energies released in nuclear events seem so huge is in part because the energy releases we are used to (like from burning a fuel) are chemical changes, which only involve changing the states of a few electrons on the outside of atoms, which contain only a tiny fraction of the atom's mass. Nuclear reactions change the states of the relatively massive particles in the nucleus of the atom, such as protons and neutrons. Hence the energies released or absorbed are vastly bigger that those we get from chemical reactions.