Understanding the Doppler Effect Equation: Velocity and Frequency Relationship

In summary, the conversation discusses the Doppler effect equation and how it applies to a person traveling towards a wall with a tuning fork at a certain frequency and speed. The question arises about the signs of the observer's speed and the source's speed, and the importance of considering the observer and source as separate entities. The conversation also touches on the fact that the effect will be different depending on whether the wall is approaching the person or the person is approaching the wall. The equation for the frequency heard by the listener also changes depending on the situation.
  • #1
dekoi
Suppose a person is traveling towards a wall with a tuning fork at frequency 'f' at a speed of 'v*'. Using the doppler effect equation:
[tex] f' \ = \frac{v + v_o}{v - v_s} [/tex]

What would the sign of v_o and v_s be? I don't understand, since the man is both the observer and the source. (Let - be receeding and + be approaching).
 
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  • #2
Treat the wall as a source which is approaching the observer. Remember that observers are aways stationary.
 
  • #3
Integral said:
Remember that observers are aways stationary.

Observers aren't always stationary though. The effect will be different if the wall approaches him than if he approaches the wall.
 
  • #4
So which is the correct answer??
 
  • #5
d_leet said:
Observers aren't always stationary though. The effect will be different if the wall approaches him than if he approaches the wall.
Why? (to b, not to a)
 
  • #6
berkeman said:
Why? (to b, not to a)

Because if the sound is moving then the waves will be closer together or farther apart than if the sound is staionary.
 
  • #7
No. In an approaching situation, the waves are compressed no matter what.
 
  • #8
berkeman said:
No. In an approaching situation, the waves are compressed no matter what.

but if f is the frequency of the source.

then f(1+ v/v_sound) is noth the same thing as f/(1 - v/v_sound) the equations are different for each situation so the frequencies heard by the listener will be different in each case.
 

FAQ: Understanding the Doppler Effect Equation: Velocity and Frequency Relationship

1. What is the Doppler effect equation?

The Doppler effect equation is a mathematical formula that describes the relationship between the velocity of a moving object and the resulting change in frequency of the sound waves it produces. It is commonly represented as f' = f(v ± vs) / (v ± vd), where f' is the observed frequency, f is the original frequency, v is the speed of sound, vs is the velocity of the source, and vd is the velocity of the detector.

2. How does the Doppler effect equation work?

The Doppler effect equation works by taking into account the relative motion between a source of sound and a detector. When the source and detector are moving towards each other, the frequency of the sound waves appears higher, and when they are moving away from each other, the frequency appears lower. This is due to the compression and stretching of the sound waves as the source and detector move closer or farther apart.

3. What is the significance of the Doppler effect equation?

The Doppler effect equation is significant because it allows scientists to accurately predict and measure the frequency of sound waves produced by moving objects. This has many practical applications, such as in radar technology, medical ultrasound, and astronomy. It also helps us understand how sound waves behave in different situations, leading to advancements in our understanding of acoustics and wave theory.

4. Can the Doppler effect equation be applied to other types of waves?

Yes, the Doppler effect equation can be applied to other types of waves besides sound waves, such as light waves. In this case, the equation is slightly modified to take into account the speed of light and the relative velocity between the source and detector. This is known as the relativistic Doppler effect and is used in fields such as astrophysics and cosmology.

5. What are some limitations of the Doppler effect equation?

While the Doppler effect equation is a useful tool for understanding the relationship between velocity and frequency, it has some limitations. It assumes that the source and detector are moving in a straight line, and it does not take into account other factors such as the medium through which the waves are traveling. Additionally, it only applies to relative motion and cannot accurately predict the frequency of stationary sources.

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