Mika is interested in the story of Isaac Newton, who, she has read, might have seen an apple falling from a tree or perhaps was hit on the head by one. That apple and seeing the Moon were supposedly what led him to think up and to develop his theory of universal gravitation. She and her friend Esperanza are intrigued with Newton's discovery that the same force that causes apples to fall is responsible for the Moon's orbiting Earth, and they want to understand more about gravitational forces