An old proverb says that "Necessity is the mother of invention." But if you look at real-life stories of technology, you'll see that not all inventions were planned. Some of them were accidents! In the 1940s, a scientist named Percy Spencer was working to develop radar systems for the U.S. military. One day, in his laboratory, he noticed that a chocolate bar in his pocket had gotten very soft and melted even though it wasn't hot in the room. He was standing next to a machine called a magnetron. Quickly, he did an experiment, putting some kernels of corn next to the magnetron. In a minute, he had popcorn. And that was how the microwave oven was invented. "Accidental inventions" have been happening for a long time. In 1839, a salesman was experimenting with a new product from Brazil called rubber. It could be used to make erasers, but it melted at high temperatures, and broke when it was cold. The inventor tried mixing it with different chemicals, but nothing worked until he accidentally dropped it on a hot stove. Heat made the rubber strong and flexible. Thanks to Charles Goodyear's accident, we now have rubber tires for our cars, and rubber soles for our shoes.