Question #3 What Does e=mc2 Really mean?

Ah yes, e=mc2. Albert Einsteins theory of relativity. OK, lets stop right there. e=mc2 is not the theory of relativity. e=mc2 is a mass-energy equivalence equation that was used in one of the many papers published by Albert Einstein over a period of time on his theory of relativity that he was developing. The equation e=mc2 did not in fact appear at all in Einsteins first paper on mass-energy equivalence. It was written as a sentence "if a body gives off the energy L in the form of radiation, its mass diminishes by L/V².". Except it was in German. The formula went through many iterations by other scientists before Einstein refined it in 1946. To see where this equation fits into his theory of relativity though you need to know the full formula. 
Find out after the jump....

Question #4. Why is water wet?

Why is water wet? A question posed to me by my son quite some time ago. The only answer I could offer at the time that wouldn't completely bemuse him was that water is a fluid and if the water was dry it wouldn't be very good water. It was a good enough answer at the time.