91热爆

Professor Brian Cox explains the first law of thermodynamics. He describes how energy is always conserved, never created or destroyed. He uses an analogy of a waterfall to explain how gravitational potential energy (for which he gives the formula) is converted into other forms. He ends with the quote, 鈥淓very single joule of energy in the universe today was present at the Big Bang 13.7 billion years ago.鈥�