RE: The Doppler Effect......
May 2, 2021 at 1:20 am
(This post was last modified: May 2, 2021 at 1:25 am by Anomalocaris.)
Think of it this way. The speed of sound in air is governed by the density of the air, not by any attribute of the device that made the sound. So If a car is moving through air from left to right, The sound propagating ahead and behind the car moves at the same speed relative to the air, not to the car.
Let’s say sound propagate through air at 1000 feet per second. Let’s say the car moves from left to right at 100 feet/sec. Now imagine if the frequency of the sound emitter by the car is 100 beats a second. The 1st beat the car made would have traveled 10 feet through the air to both the left and right by the time the second beat is emitted. But during the intervening time the car would have also traveled 1 foot or the right.
So when the second beat is emitted by the car, the second beat would follow the first beat not by 10 feet, but only 9 feet at the right, but 11 feet at the left because the car itself has moved in between the beats.
So what does that mean? Now imagine you are stationary WRT the air to the right of the car. The beats of the sound is arriving at your location at 1000 feet per second, separated by 9 feet between each beat. What is the frenquecy you hear? It is 1000/9=111 beats a second. Now imagine you are a stationary listener to,the left of the car. The beats of the sound is arriving at your location at 1000 feet per second, separated by 11 feet between each beat. What is the frenquecy you hear? It is 1000/11=90 beats a second.
Frequency increase in front of a moving emitter, and decrease behind a moving emitter, as measured by an listener at rest with respect to the medium in which the wave travels.
So that is Doppler effect.
Volume is how loud the scream is. Pitch is how sharp the scream is.
Imagine someone is screaming. Volume is how loud the scream is. Pitch is how sharp the scream is.
Let’s say sound propagate through air at 1000 feet per second. Let’s say the car moves from left to right at 100 feet/sec. Now imagine if the frequency of the sound emitter by the car is 100 beats a second. The 1st beat the car made would have traveled 10 feet through the air to both the left and right by the time the second beat is emitted. But during the intervening time the car would have also traveled 1 foot or the right.
So when the second beat is emitted by the car, the second beat would follow the first beat not by 10 feet, but only 9 feet at the right, but 11 feet at the left because the car itself has moved in between the beats.
So what does that mean? Now imagine you are stationary WRT the air to the right of the car. The beats of the sound is arriving at your location at 1000 feet per second, separated by 9 feet between each beat. What is the frenquecy you hear? It is 1000/9=111 beats a second. Now imagine you are a stationary listener to,the left of the car. The beats of the sound is arriving at your location at 1000 feet per second, separated by 11 feet between each beat. What is the frenquecy you hear? It is 1000/11=90 beats a second.
Frequency increase in front of a moving emitter, and decrease behind a moving emitter, as measured by an listener at rest with respect to the medium in which the wave travels.
So that is Doppler effect.
(May 1, 2021 at 11:09 pm)Brian37 Wrote:(May 1, 2021 at 11:05 pm)Jackalope Wrote: It's not volume, it's pitch.
Ok, without making my head explode, what is the difference between volume and pitch?
Because no matter my motion, standing still, or being in motion myself, I do know somthing off in the distance I am not going to percieve as being as loud as something right next to me. And as well, after it passes me and moves off in the distance it I will not percieve it as loud as if both of us were stationary right next to each other.
Volume is how loud the scream is. Pitch is how sharp the scream is.
(May 1, 2021 at 11:09 pm)Brian37 Wrote:(May 1, 2021 at 11:05 pm)Jackalope Wrote: It's not volume, it's pitch.
Ok, without making my head explode, what is the difference between volume and pitch?
Because no matter my motion, standing still, or being in motion myself, I do know somthing off in the distance I am not going to percieve as being as loud as something right next to me. And as well, after it passes me and moves off in the distance it I will not percieve it as loud as if both of us were stationary right next to each other.
Imagine someone is screaming. Volume is how loud the scream is. Pitch is how sharp the scream is.
