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billybrobby
Joined: 09 Dec 2004
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 Posted: Sat Apr 22, 2006 4:47 am Post subject: Re: questions about stupid s#!)t |
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| tzechuk wrote: |
| Bronski wrote: |
| khyber wrote: |
I have a couple questions i don't get:
1) Why is it that if you drink cold water, it feels MUCH COLDER in your mouth if you drink if faster?
2) Why is it that ambulance sirens seem to change pitch as the approach you and as they drive behind you?
answers?
more questions? |
1) It probably has to do with your mouth adjusting to the temperature. Like if you ease into a hot tub it won't feel as hot as if you jump in.
2) That's called the Doppler Effect: http://en.wikipedia.org/wiki/Doppler_effect
| Quote: |
The siren on a passing emergency vehicle will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer. Astronomer John Dobson explained the effect thus:
"The reason the siren slides is because it doesn't hit you."
In other words, if the siren approached you directly, the pitch would remain constant (as vs, r is only the radial component) until the vehicle hit you, and then immediately jump to a new lower pitch. The difference between the higher pitch and rest pitch would be the same as the lower pitch and rest pitch. Because the vehicle passes by you, the radial velocity does not remain constant, but instead varies as a function of the angle between your line of sight and the siren's velocity:
where vs is the velocity of the object (source of waves) with respect to the medium, and �� is the angle between the object's forward velocity and the line of sight from the object to the observer. |
I don't entirely understand it, but I know that it happens. You can notice it with regular vehicles passing as well, but it's not as obvious. |
Might be easier to explain it that sound waves change frequency depending on the distance. So if it is far from you, it is one sound; it is is close to you, it is another. Then when it moves away from you, the frequency changes again, so you hear a different sound again.
That's the nutshell of the doppler effect. |
that's totally not how the doppler effect works. |
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Hanson
Joined: 20 Oct 2004
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| Posted: Sat Apr 22, 2006 5:20 am Post subject: |
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| Why did Japanese kamikaze pilots wear helmets? |
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CaptainConjunction
Joined: 12 Oct 2005
Location: Seoul
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| Posted: Sat Apr 22, 2006 6:22 am Post subject: Re: questions about stupid s#!)t |
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| tzechuk wrote: |
| Bronski wrote: |
| khyber wrote: |
I have a couple questions i don't get:
1) Why is it that if you drink cold water, it feels MUCH COLDER in your mouth if you drink if faster?
2) Why is it that ambulance sirens seem to change pitch as the approach you and as they drive behind you?
answers?
more questions? |
1) It probably has to do with your mouth adjusting to the temperature. Like if you ease into a hot tub it won't feel as hot as if you jump in.
2) That's called the Doppler Effect: http://en.wikipedia.org/wiki/Doppler_effect
| Quote: |
The siren on a passing emergency vehicle will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer. Astronomer John Dobson explained the effect thus:
"The reason the siren slides is because it doesn't hit you."
In other words, if the siren approached you directly, the pitch would remain constant (as vs, r is only the radial component) until the vehicle hit you, and then immediately jump to a new lower pitch. The difference between the higher pitch and rest pitch would be the same as the lower pitch and rest pitch. Because the vehicle passes by you, the radial velocity does not remain constant, but instead varies as a function of the angle between your line of sight and the siren's velocity:
where vs is the velocity of the object (source of waves) with respect to the medium, and �� is the angle between the object's forward velocity and the line of sight from the object to the observer. |
I don't entirely understand it, but I know that it happens. You can notice it with regular vehicles passing as well, but it's not as obvious. |
Might be easier to explain it that sound waves change frequency depending on the distance. So if it is far from you, it is one sound; it is is close to you, it is another. Then when it moves away from you, the frequency changes again, so you hear a different sound again.
That's the nutshell of the doppler effect. |
The main thing you need to know is that when someone asks this kind of question, just say "It's because of the Doppler Effect".. and then smile knowingly and change the subject.  |
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doggyji
Joined: 21 Feb 2006
Location: Toronto - Hamilton - Vineland - St. Catherines
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| Posted: Sat Apr 22, 2006 1:43 pm Post subject: Re: questions about stupid s#!)t |
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| doggyji wrote: |
| From my understanding, as long as the sound source is the same, the sound wave's intrinsic frequency remains unchanged. It's all about how you get it in a "relative motion." It happens because it's moving. There are sirens A and B. Both of them have the same frequency, 100Hz. Now A is moving towards you from distance and B is stationary 10 meters away from you. Of course, you get the same 100Hz from B(just a bit less amplitude due to dissipations/damping) because there's no relative motion. You and siren B are in the same inertial frame.And imagine the moment when A exactly passes the point where B is placed. Same distance, same sound source but you don't get 100Hz in your ears. It's not like at this distance it has this unique frequency. The motion relative to you is the key. |
By the way, I didn't really have to bring up the term 'inertial frame' as if we are considering any acceleration here. Nitpicking technicality's all that matters in science anyway. |
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little mixed girl
Joined: 11 Jun 2003
Location: shin hyesung's bed~
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| Posted: Sat Apr 22, 2006 1:53 pm Post subject: |
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| Quote: |
| 2) Why is it that ambulance sirens seem to change pitch as the approach you and as they drive behind you? |
the doppler effect.
dammit i see someone beat me to it!  |
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