On Friday we posed an interesting puzzle for you to ponder. A very simple puzzle to state, but it leads to all sorts of debates and arguments. As we said, it is a good one to ask in the pub!
Here’s the puzzle
A person is sitting in a rowing boat that is floating in an artificial pool, and they are holding a brick. The person throws the brick out of the boat into the water, and it sinks to the bottom. Once the ripples have died away, has the water level risen, fallen or stayed the same?
When in the boat the brick displaces a volume of water equal in weight to itself. When it is on the bottom of the swimming pool it displaces a volume of water equal to its volume. As the brick has sunk, it is denser than water, so the volume of water equal to the brick’s weight is bigger than the brick’s volume. In the boat it displaces more water than it does when in the swimming pool, so the level of water in the pool falls.