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When you turned right, the helium balloon moved right, didn't it? (And it was kind of creepy, wasn't it?, like Pennywise the Clown's balloons in the storm drain in Stephen King's IT.)
The reason your balloon went the "wrong" way is that air too has mass, and even though you can't feel the effect, when you turn right the air in the car moves left, just as your body does.
And when that air piles up on the left side of the car, it creates a pressure difference between the left side of the car and the right side. The left side has a higher air pressure and the right side has a lower air pressure. Objects that are not restrained from doing so by some more powerful force will always move from an area of high pressure to an adjacent area of low pressure, which is just what the balloon does. The high-pressure air on the left pushes the lighter-than-air balloon to the right, or, said another way, the relative vacuum on the right sucks the balloon into it.
Neat, eh? And a little eerie.
You know how the weatherman is all the time telling you about the barometric pressure. He'll say it's 30 and rising, or 31 and falling, or some such thing. Do you know how to interpret that information? Most people don't. The reason you should care rather than yawn, if you want to know what the weather is going to do, is because of that same law that says objects tend to move from areas of high pressure to adjacent areas of low pressure. If the barometric pressure is falling in your vicinity, that means the "weather" by which I mean clouds and rain and snow and such, i.e., bad weather as opposed to clear skies -- is moving away from wherever the nearest areas of high pressure are and toward you. Short course: High pressure good, low pressure bad.
Here's another experiment involving helium.
Experiment. Inhale helium from a helium balloon and talk. As surely almost all of you know, your voice is way higher and cartoonish-sounding. But why?
When you talk without helium in your lungs, i.e., when you talk by exhaling normal air, your voice has a certain pitch range. That range is determined in part by the density of that air you're exhaling. The higher the density of that air, the lower is the pitch and the faster is the speed of sound, so if you talk while exhaling helium, which has less density (less mass per unit of volume) than air (which is about 78% nitrogen), the pitch rises.
Here's what the March 1987 edition of Scientific American says in an article titled "Sopranos of the Skies":
When a soprano sings a high C, her vocal cords actually produce a broad band of frequencies. . . . If [she] inhales helium, her voice seems to rise in pitch not because her vocal cords vibrate faster in the less dense atmosphere (they do, but only slightly); rather, because sound travels almost twice as fast through helium as it does through nitrogen, the acoustic properties of the vocal tract change so that it resonates with and amplifies higher-frequency tones.
Experiment. Here's yet another experiment you can run. If a less dense medium raises the pitch of sound, then thunder should be higher-pitched at higher altitudes, where the air is less dense. Next time you're on a 747, wait till the pilot announces that you've reached cruising altitude, which will be around 35,000 feet. Then simply ask the pilot to fly straight toward the nearest thunderstorm. When you get there, merely stick your head out the cockpit window and listen to the thunder for a few minutes. You'll notice that it has a distinctly higher pitch than at, say, sea level.
That's also why foghorns sound so low in pitch, at least when they're blown in actual fog. Go to your nearest full-service lighthouse, chat up the operator, and ask him to blow his horn for you in the fog, then tape record it. The have him blow his horn when it's not foggy and tape record that. Compare the two and you'll hear that the sound of the horn is lower when it was foggy.
Speaking of fog, here's a purported log of radio transmissions during a pea-souper off the coast of South Carolina.
Radioman 1: Ahoy. You are on a
head-on collision course with us. Divert your heading 10 degrees west.
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