If I drop a vibrating 440 Hz tuning fork down the elevator shaft

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Discussion Overview

The discussion revolves around the scenario of dropping a vibrating 440 Hz tuning fork down an elevator shaft and whether the frequency heard (400 Hz) can be used to determine how far the tuning fork has fallen. The conversation touches on concepts related to the Doppler effect and gravitational free fall.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant questions whether it is possible to determine the distance fallen based on the frequency heard, suggesting uncertainty in their friend's assertion.
  • Another participant asserts that the frequency can be used to find the velocity of the tuning fork through the Doppler effect, which can then be used to calculate the time of free fall and subsequently the distance fallen, while neglecting air resistance.
  • A participant requests proof of the previous claim, indicating a desire for validation of the method proposed.
  • In response, a participant clarifies that the term 'proof' may not apply in this context, suggesting a philosophical consideration of scientific proof.
  • A mathematical expression for the Doppler shift is provided, indicating the relationship between the observed frequency and the speed of the tuning fork.
  • Another participant introduces a correction regarding the calculation of height, suggesting that the time delay for sound must be accounted for, leading to a modified equation for height.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of determining the distance fallen based on the frequency heard, with some supporting the idea and others questioning it. The discussion remains unresolved with competing perspectives on the application of the Doppler effect and the effects of sound delay.

Contextual Notes

There are limitations regarding assumptions made about air resistance and the definitions of terms used in the mathematical expressions. The discussion also highlights unresolved mathematical steps related to the calculations presented.

david90
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if I drop a vibrating 440 Hz tuning fork down the elevator shaft of a tall building and when I hear a freq. of 400 Hz, is it possible to determine how far has the tuning fork fallen? My friend said yes but I think no. Am i right?
 
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Yep. You can use the frequency to find the velocity (via the Doppler effect) and the velocity to find the time in gravitational free fall and thus the distance. (Neglecting air resistance and so on in normal physical fashion.)

- Warren
 
u have proof of that?
 
Proof? I'm afraid the scientific definition of the word 'proof' doesn't apply here.

- Warren
 
The Doppler shift here is given by freq0*vs / (vs+vfork) where vs~345 m/s, the speed of sound. so 400/440 = 345/(345+vfork).

Then you use distance=vfork^2/19.6
 
Actually due to time delay for sound to get to you it is not h(v)=(v2/2g) but h(v)=(v2/2g)(1+v/2c)2
 

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