# Realistic explanation of the doppler effect

1. Jan 27, 2010

### Moroni

Could anyone who knows give me a really simple yet realistic explanation of the doppler effect. This is one of those things that just boggles the brain so to speak.

2. Jan 27, 2010

### Andrew Mason

With a source moving through a sound medium (eg. air), the wavelength of the sound in the medium increases in the direction opposite to the motion and decreases in the direction of the motion. This is because in the time between vibrations, T = 1/f, the source moves a distance s = vT. Thus the wavelength in the direction of sound is reduced by vT and the wavelength opposite to the direction of sound is increased by vT.

See:http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html#c1

AM

3. Jan 27, 2010

### dacruick

the best way that I can think to explain it to you is like this.

if you are travelling towards a source while emitting sound, the sine function that the sound travels in gets compressed. This means that there is a higher frequency.

if you are travelling away from a source the opposite happens.

Also, it might help to evaluate this situation at the speed of sound. Imagine you are travelling towards a person at the speed of sound. All the sound that you emit that whole time will in a sense be travelling with you, and reach that person all at once. Conversely, if you are travelling twice the speed of sound, the sound that the person will hear will be in reverse of the way you played it. just think this concept over and let me know if you have any questions

4. Jan 27, 2010

### dacruick

and ill correct my use of the word conversely, and replace it with 'also'. I think i just used that word because I wanted to feel sophisticated

5. Jan 28, 2010

### Moroni

Thank You both very much.

My one question is, from what I understand then, if I'm moving (slower than the speed of sound,) then the sound will reach another object before or after I do?

You have helped me a lot and I appreciate it!

6. Jan 28, 2010

### Andrew Mason

I think you can figure that out. If the speed of sound is faster than your speed, will the sound travel farther than you or will you travel farther than the sound in a given time?

AM

7. Jan 29, 2010

### Moroni

That Makes Sense Thanks! I just wanted to clarify.