# Swinging fans & Doppler's shift

• TharitTk
In summary, the conversation discusses the impact of wind speed on the Doppler effect of sound waves generated by a swinging fan. The question raises uncertainty about the speed of the source and the change in the wave solution when affected by wind speed. It is determined that the apparent source of the sound will be affected by the movement of the air and its speed towards or away from the listener. The specific calculations for these effects depend on the distance of the listener from the fan and the fan's angle.
TharitTk

## Homework Statement

http://postimage.org/][/PLAIN]

## The Attempt at a Solution

I consider that if the fan is swinging, the source of sound (fan) will have an speed that lead to doppler's shift.
but i can't calculate for this. i think speed of source will be ωR cos (ωt) (R is the radius of fan's swinging) but there is no data of R . I only know that in question 3 will answer nearly constant with time becuse source of sound will be a spot and we neglet the speed from swinging.

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I am not sure. What change on the wave solution:

$$A(x,t) = A\sin(\omega{t}-kx)$$

by wind speed, ##\omega## or ##k##?

The flow of air makes this a tricky question. If you think of the wave fronts leaving the wire cage, they get carried by the flow of air as well as traveling through it. Consider a wavefront generated at time t, in some parcel of air P that comes through the wire. The wavefront's arc will continue to be centred on P as P moves. Thus, when it reaches the listener, it will be as though it has come from where P now is.
If the listener is at distance D from the fan (large compared with fan size), how long does it take for the sound to reach the listener? Where will the corresponding apparent source be then? How fast will the apparent source be moving towards or away from the listener (it will depend on the fan angle)?

## 1. What is a swinging fan?

A swinging fan is a device that consists of a rotating fan attached to a string or rod. When the fan rotates, it creates a Doppler effect, causing the sound it produces to change in pitch depending on the direction of its rotation.

## 2. What is the Doppler effect?

The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. This effect can be seen in various phenomena, such as the change in pitch of a siren as it passes by.

## 3. How does a swinging fan produce a Doppler effect?

As the fan rotates, the blades move towards and away from the observer, causing a change in the frequency of the sound it produces. When the blades move towards the observer, the frequency increases, and when they move away, the frequency decreases.

## 4. What is the significance of Doppler's shift in science?

Doppler's shift is significant in various fields of science, including astronomy, meteorology, and acoustics. It allows scientists to determine the velocity and direction of objects, measure wind speeds, and study the behavior of sound waves.

## 5. Can the Doppler effect be observed in other situations besides a swinging fan?

Yes, the Doppler effect can be observed in various situations, such as the movement of stars and galaxies in astronomy, the change in frequency of radio waves in telecommunications, and the change in pitch of a moving vehicle's horn or siren.

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