Sunday, December 20, 2009

Science fun, Vol. 2: Sound science

This is not a post about global warming or greenhouse gases or whether the level of trans fats in a tasty salty snack make a significant difference in a person gaining weight or not. This is about the science of sound.

Here's the thing. Science is hard. Compared to science, math is easy. If you get the work right in math, there are no arguments. It might be there is another way to solve the same math problem, but it has to come up with the same solution or one of the two ways is wrong. But science is trickier, and even when we get an explanation that works in science, this doesn't mean we understand the whole problem. Sometimes theories get overturned completely or they get fine tuned. That is the nature of scientific inquiry.


What causes thunder? Common sense tells us that whatever causes lightning must cause thunder, and that's true as far as it goes. Technically, the accepted scientific explanation of today is that atmospheric conditions cause lightning and lightning then causes thunder almost instantaneously. This is one of those fine tuning things.

Common sense tells us that for a noise that loud to occur, there must have been a collision of two solid objects. Aristotle believed it was the sound made when two clouds collided, and I was taught something like that when I was in school about fifty years ago. It's not the accepted theory today. In a lot of fields of science, you have to throw common sense away because incredibly powerful forces often have unseen causes.

The cause of lightning is still a strongly debated topic in science. The standard theory argues that it has to do with positive and negative charges in the water in a rain storm, some of it turning to ice crystals and getting an opposite electric charge to the water that remains in liquid form. Another theory postulates the objects with opposite charges are the ground and parts of the cloud. Others think cosmic rays are involved.

The cause of thunder is less controversial, but still not completely nailed down to everyone's satisfaction. Lightning is incredibly hot, and superheats the air around the bolt, dramatically changing the pressure which creates a shock wave. The "rolling" effect to the sound is due to the length of a lightning bolt, the sound of multiple shock waves at varying distances away from the listener. There are some who argue the numbers don't quite add up, and there must be other forces at play, probably electrodynamic in nature.



And then there's that other loud noise in the sky, the much rarer sonic boom. Again, common sense would tell us something solid and big hit something else solid and big. As often happens, common sense doesn't help much here. A jet is a very big thing and if it collides with something, it makes a hell of a racket and disintegrates. But the sonic boom is the collision of two non-solid things created by the jet, the bow wave and the stern wave, both of which travel at the speed of sound. As the jet moves faster than the speed of sound, the two waves collide and produce the sound. There is no "rolling" sound effect because the source is a single, relatively small object.

Earlier I wrote about unseen causes creating massive effects. Technically, if you are close enough to a jet breaking the sound barrier, you'll see the plane pass through a ring of water vapor, so it isn't actually unseen. But to be slightly more technical, using the evidence of our eyes we might think the sound is the plane hitting that previously unseen wall of water vapor, when the actual cause of the sound is the cause of the circle of vapor, the two otherwise invisible and relatively quiet pressure waves being forced together for a split second.

Let me repeat. Science is hard. I've simplified this quite a bit, and some of my more science-y pals might very well stop by to tell me I've over-simplified. Any science discussion that makes it to the newspapers is simplified, and if there's a controversy, there will likely be over-simplifiers on both sides. But in so many "controversies" today, it's the over-simplifiers vs. the wishful thinkers, and wishful thinking is not science at all.

2 comments:

¡Karlacita! said...

When I did radio news in Monterey in 2007, I decided to bring science and medical stories into the broadcasts.

And Wow! The science reporting most people read is not only wrong, it's crazy wrong! I bopped over to the actual studies that the reported articles were culled from, and just went - whoa!

I'd go so far as to say that it is astonishing when most reporters get a science story right. And you know what the big problems is, besides laziness?

They don't understand statistics.

dguzman said...

I've read a lot about meteorology, and I still don't get the whole lightning/thunder thing. I used to like the clouds banging into each other theory that I too was taught; it made some sense. But you're right: science's sense is often too hard to comprehend.

And Karlacita is right; hardly anyone understands statistics. I know very little (the product of being with a statistician for six-and-half-years), but even I can tell when reporters are just plain wrong in their analyses of the numbers.