When transmitter & receiver move in same direction with same velocity

Interesting question. I think the motions of the transmitter and receiver are relative to each other. When both transmitter and receiver are moving in the same direction with same velocity, they are stationary relative to each other and I *think* the frequency shouldn't change.

Tagging #-Link-Snipped-# , for confirmation. 😒

The_Big_KInteresting question. I think the motions of the transmitter and receiver are relative to each other. When both transmitter and receiver are moving in the same direction with same velocity, they are stationary relative to each other and I *think* the frequency shouldn't change.

Tagging #-Link-Snipped-# , for confirmation. 😒

Right you are. The two are stationary as far as they are concerned.
The usual high to low transition of a train's whistle as it passes us that we are all familiar with is the higher pitch of the whistle as the train is coming towards us and the sharp drop as it speeds away from us is because of the change in velocity between the transmitter and the receiver.
The 'Red Shift' that we observe of astronomical objects from which the expansion of the universe is studied is a fixed variation in frequency as the transmitter is moving away at a constant velocity (for the moment anyway).
Quote:
The Doppler Redshift results from the relative motion of the light emitting object and the observer. If the source of light is moving away from you then the wavelength of the light is stretched out, i.e., the light is shifted towards the red. These effects, individually called the blueshift, and the redshift are together known as doppler shifts. The shift in the wavelength is given by a simple formula
(Observed wavelength - Rest wavelength)/(Rest wavelength) = (v/c)
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endquote

When the magnitude and direction are the same then the resultant velocity difference cancels each other and so there is Actually no change in the distance between both the listener and the source.

Doppler effect uses this distance shift to a great extent Since the distance is always constant the changes are not seen.

PS: Provided environmental effects are negligible

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sir,can you explain me what is meant by rest wavelength??

from the above answers it is clear that since the relative velocity is zero there is no change in frequency..actually the bodies are stationary to each other but they do have certain velocity isn't it?then wont this velocity (though constant) have any effect on frequency?

Yeah you almost got it You need a relative variation in velocity to alter the frequency. When this relative variation is 0 we have nearly constant frequency in the reception side

(Observed wavelength - Rest wavelength)/(Rest wavelength) = (v/c)
In the above equation if v=0 (No relative motion) (v/c)=0/c=0, which means that there is no change in frequency. The value of v could be nearly = c. Even then there in no effect on the frequency with respect to the two bodies between themselves.However, a stationary (relative to these two) object will see a change in frequency for the same signal.

gwendollen#-Link-Snipped-#
sir,can you explain me what is meant by rest wavelength??

Rest wave length is the wavelength that is measured between receiver and transmitter on the same body.