Absolutely correct Rob. I feel a physics lesson coming on 
A more practical example of mass-energy equivalence:
The mass of an atom is less than the sum of the masses of it's component protons & neutrons. The difference is called "binding energy". That's the energy required to separate a nucleus into a bunch of protons and neutrons. It's also the energy released when a bunch of protons and neutrons are assembled into a nucleus.
The binding energy per particle is highest for medium sized atoms like iron, and lower for heavy atoms like uranium, and also lower for very light atoms like hydrogen.
So if you take an atom of uranium and split it into two smaller atoms, that's equivalent to separating its nucleus into a bunch of protons and neutrons, and then assembling two smaller nuclei from them. Due to different binding energy, the two product nuclei together weigh a bit less than the original uranium atom, and a lot of energy is released.
Making the same argument, if you take a couple of hydrogen atoms and force them together to make one heavier helium atom, it weighs a bit less than the original hydrogen atoms, and a lot of energy is released.
Whence cometh fission bombs, fusion bombs (AKA thermonuclear), controlled nuclear fission (like the reactors at Bruce), and maybe someday, controlled nuclear fusion reactors.
73
Dave, VE3WI
A more practical example of mass-energy equivalence:
The mass of an atom is less than the sum of the masses of it's component protons & neutrons. The difference is called "binding energy". That's the energy required to separate a nucleus into a bunch of protons and neutrons. It's also the energy released when a bunch of protons and neutrons are assembled into a nucleus.
The binding energy per particle is highest for medium sized atoms like iron, and lower for heavy atoms like uranium, and also lower for very light atoms like hydrogen.
So if you take an atom of uranium and split it into two smaller atoms, that's equivalent to separating its nucleus into a bunch of protons and neutrons, and then assembling two smaller nuclei from them. Due to different binding energy, the two product nuclei together weigh a bit less than the original uranium atom, and a lot of energy is released.
Making the same argument, if you take a couple of hydrogen atoms and force them together to make one heavier helium atom, it weighs a bit less than the original hydrogen atoms, and a lot of energy is released.
Whence cometh fission bombs, fusion bombs (AKA thermonuclear), controlled nuclear fission (like the reactors at Bruce), and maybe someday, controlled nuclear fusion reactors.
73
Dave, VE3WI