A sonic boom is created when an object travels faster than the speed of sound. When an airplane reaches the speed of sound, it makes a bang sound or an explosive noise it can be seen with the naked eye. This is often called "breaking the sound barrier." The visible part of a sonic boom is actually air that becomes squashed by sound waves. The thunder that a storm makes is also a sonic boom caused by lightning forcing air to move faster than the speed of sound.
- "The Science of Thunder". Retrieved 2008-06-17.