Sonic Booms Explained
I was trying to explain to someone how a sonic boom works when a jet breaks the sound barrier. Usually when I do that once, I like to document it here on the blog. In this case, I actually found a great video that lays it all out!
When an object passes through the air, it creates a series of pressure waves in front of it and behind it, similar to the bow and stern waves created by a boat. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot “get out of the way” of each other, eventually merging into a single shock wave at the speed of sound. This critical speed is known as Mach 1 and is approximately 1,225 kilometers per hour (761 mph) at sea level.
Now, if you want to make your own sonic boom, just go to a western store and pick up a bull whip. When you crack the whip you’re actually putting enough energy into the tip that it travels faster than the speed of sound. In fact, he whip was the first human invention to break the sound barrier.
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Other things that produce sonic booms:
* Propellers on prop airplanes. The tips can move fast enough to break the sound barrier.
* Helicopter blades. Although I think it’s dangerous for the tips of the rotors to break the sound barrier.
Aaron Hall – article is very interesting and helps me in my scientific word in Russia!
I like the way you think, Armen!!! A very philosophical take on barriers indeed!
I like how the video presents it in a straightforward way. The point about the whip brings it home with an example that we have surely heard. Barriers are crossed in different ways every so often, and when they are, we see another element of nature or our environment showing itself off. Not too long after, a new discovery becomes an expected occurrence.
That is very interesting. One researcher who examined the sonic boom of a bull whip noted that “the tip can reach speeds more than 30 times the initial speed [of the whip].” Source: http://www.sciam.com/article.cfm?id=true-cause-of-whips-crack
Jackie,
It’s just the volume of air involved. The tip of a whip is so small that the amount of air deflected is tiny. But the mass of the plane pushing through the air is substantially larger. Plus, the plane is going to sustain Mach 1+ while the whip just manages to do it and then it’s over. :-)
John
but why then is it a low sound when planes break the sound barrier and a high sound when a whip cracks the barrier? shouldn’t/wouldn’t it be the same sound?