HAVING A BLAST READING id

Even when I come across a topic I wouldn’t think I’d be interested in, you find a way to make it appealing. So I can honestly say, I’ve never met a story in id that I didn’t like. Most recently there was an article on “The Anatomy of an Explosion” in the September issue; I don’t know much about how explosives work, so this article was a good primer. But one thing that confuses me is the difference between pressure waves, shock waves, and blast waves. Which is which? Robert Markovic, Dearborn, MI

Pressure wave is the general term for any energy-carrying wave that moves through a medium, such as air or water, so basically any disturbance that results in a change in pressure of the medium through which it travels effectively propagates into a pressure wave. One example is a sound wave because it’s a fluctuating pattern of high- and low-pressure zones.

A shock wave is also an energy-carrying wave that travels through a medium. A characteristic of a shock wave is that it moves faster than the speed of sound and effectuates a sudden change in the pressure, temperature, and density of the medium through which it propagates. Another feature is the sonic boom that’s heard when an object, such as a plane, travels faster than the speed of sound. Multiple pressure waves compress into one shock wave that moves faster than the speed of sound and precipitates a huge pressure change. A blast wave results from an explosion, which releases a lot of energy. It entails an abrupt pressure rise and creates negative pressure in its wake. At its leading edge is compressed gas.