Imagine you and your friends are at an air show. You've been
waiting all day to catch a glimpse of the famous SR-71
Blackbird, the fastest plane in the world. The announcer
reports that it's now overhead—but you can't see it
because it's flying so fast! After about a minute, you hear
an enormous "BOOM," louder than any thunder or fireworks
you've ever heard! What do you think made the noise
happen?