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- University of Manitoba: Sound waves
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3 Comments
You should have paid better attention in physics class. Here's why this is totally wrong...again.
What you're trying to imply, I think, is that if you shout something to the west, the rotation of the Earth will cause the sound wave to cover more ground, since the Earth is rotating "toward" the sound source. If you shout to the east, the Earth will be rotating "away from" you, and so the sound will not cover as much ground before running out of energy.
Let's suppose that were true. Sound travels through air at about 340 m/s. The Earth rotates at a speed of 464 m/s at the equator. Let's pretend that you're standing at the equator and blow a horn that produces a note of middle C. By your reasoning, a person standing to your west would be hit by sound moving at 804 m/s, since they are rotating "into" the wave. Since they perceive the wave as moving faster, they would also see its crests and troughs as arriving closer together. In other words, its frequency (and therefore its pitch) would have to increase.
And what about an observer standing to the east? He's rotating "away from" the wave faster than the wave itself is moving. He'll never hear the sound!
Experience tells us that this doesn't happen. If I stand on the equator and blow a horn, observers standing at equal distances to the east AND west will hear me at the same loudness. This is because the air is rotating along with the Earth. The speed of the wave, 340 m/s, is relative to the air, and NOT to some fixed point.
Now, if I blow a horn and somebody runs toward me (from ANY direction), then passes me, they will hear the pitch of the horn shift from high to low. That's called the Doppler effect, but it has to do with the observer's speed, not the Earth's.
By
Anonymous, at June 01, 2007 6:25 PM
The anonymous dude is very right - I'm impressed by the level of intelligence for a comment on this website
By
Adam, at February 05, 2010 12:45 PM
I agree that this won't happen - if the sound wave is travelling directly east or west, it will travel through the local air. The rotation of the earth doesn't matter.
If the sound waves are traveling north/south, however, the coriolis effect occurs.
A sound wave traveling away from the equator will curve somewhat to the east. A wave (or bird, or plane, or air mass) traveling towards the equator will curve to the west.
You have to travel a long way to feel the effect (it creates high and low pressure circulation, for example - at the scale of hundreds of miles). Perhaps a sound like that of Krakatoa, which was heard in England, would have curved towards the Americas in far north or south lattitudes to a measurable degree?
By
Anonymous, at February 23, 2010 12:50 AM
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