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 such 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". http://www.lightningsafety.com/nlsi_info/thunder2.html. Retrieved 2008-06-17.