Doppler shift source velocity components

1. Apr 13, 2017

undividable

1. The problem statement, all variables and given/known data
Why does a source moving perpendicular to the line between it and the observer produce no doppler effect?

2. Relevant equations

3. The attempt at a solution
I have heard the the radial velocity of the source relative to the observer must be zero but i dont understand why, if the distance between the source and the observer is increasing or decreasing , shouldn't there be a doppler effect since the wave length is changing?

2. Apr 13, 2017

PeroK

Have you tried to figure out what sort of motion that represents?

3. Apr 13, 2017

scottdave

Try to think of a type of motion, where one object is stationary, and the other object is always moving, yet does not get any closer or farther from the fixed point.

4. Apr 14, 2017

undividable

i guess my real question is, how does the doppler effect work when the observer and source are not moving in a straight line, what do we take in as the velocity of the observer and the source in the doppler effect equation?