explain why we notice the Doppler Effect for sound but not light.
well there are two ways to produce the Doppler Effect with sound 1) the listener can move toward (or away) from the source effectively changing the speed at which the sound waves are intercepted 2) the source can move toward or away from the listener effectively changing the wavelength of the intercepted waves at low speeds the effects are nearly the same but consider moving at the speed of sound consider condition 1 where listener moves away from the source at the speed of sound the result will be that no sound is heard but under condition 2 if the source moves away from the listener at the speed or sound the result will be a drop in frequency of one octave (1/2 original frequency) now with light the perceived speed is a constant, c, it is always c ! and no matter whether the observer or the source is moving the speed of light is a constant with respect to the observer so only condition 2) of the Doppler Effect prevails for light as a result if observer and source are moving apart, wavelength increases - red shift if observer and source are coming closer, wavelength decreases - blue shift Yeah, there is a Doppler Effect for light ! but just the one kind
The word notice is the key. In a boiler shop you drop a needle on the floor. Do you hear it? Yet do the same thing in a quiet room and you hear it easily. The amount of the change in the boiler shop is not sufficient for you to notice it. The same is true with the doppler effect. The percentage change for sound is quite significant for objects moving on the surface of the earth. The speed of the objects is a noticeable fraction of the speed of sound. But the speed of light is so high that normal objects you interact with do not have a speed that is a noticeable fraction of the speed of light. So we are only able to observe the doppler effect for astronomical objects that have far higher relative velocities.
We do notice a Doppler effect for light but the object emitting the light must be moving at a much higher velocity for our eyes to detect a color shift.
