A man is in a rowing boat floating on a lake. In the boat he has a brick. He throws the brick over the side of the boat so as it lands in the water and sinks. As a result of this action, does the water level in the lake go up, go down or stay the same?
Solution: The level of water in the lake goes down. This is because when the brick was in the boat, it displaced a volume of water equal to its weight. Since the brick is denser than water, the amount of water it displaces when in the boat is more than what it would displace if it sank. So, the level of water in the lake goes down.