Eight Coins, One Heavier: Two Weighings

You have 8 identical-looking coins. Exactly one of them is heavier than the rest. You have a balance scale and may use it at most 2 times. 1. Design a strategy that always identifies the heavier coin in at most 2 weighings. 2. Prove that 2 weighings are sufficient (your strategy does it) and that 1 weighing is not sufficient.