Why do objects whistle when falling? Like here.

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In summary, the conversation discusses the physics of falling objects and the sound they produce. The participants examine a video of a bullet hitting a target and discuss the vibrations and aerodynamics of the bullet as well as the sound produced by the air passing through the gaps and the Doppler effect. They also discuss the possibility of the bullet itself vibrating and creating sound, and a frequency analysis is run on the sound in the video. The conversation concludes with a discussion on the chaotic tumbling of deformed bullets and their contribution to the overall sound.
  • #1
luxun2
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This is my first post but just as it says in the title I'm curious about the physics behind falling objects. Specifically if you could examine this video which despite the title is not actually graphic and school me on why we heard what we did, Thanks.

http://www.youtube.com/watch?v=0ABGIJwiGBc

 
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  • #2
Do you know what sound is? I don't mean "something we can hear", I mean, do you know how sound is produced and transmitted?
 
  • #3
have a think about what would happen to the shape of the bullet after its impact/ricochet
and how that shape may cause a whistling sound


Dave
 
  • #4
Alrighty, well sound in my mind are the vibrations that propagate through air, water, and solids. If the bullet was shot then I would assume when it hit the target it became deformed like so(http://www.dreamstime.com/stock-image-deformed-flattened-out-bullets-image28978371) and therefore less aerodynamic. I believe either that the bullet struck the iron so that the bullet vibrated at its resonate frequency or the bullet is now displacing a lot of air and it is merely the wind that we are hearing along with the Doppler effect.
 
  • #5
you don't have to get as complicated as resonant freq or Doppler effects

look at that deformed bullet 5th image along ... see all the ragged edges/bits curled out
The air is literally going to create a whistling sound as it moves through the gaps

similar to when you blow air through your slightly opened lips to whistle or blow air across an open top of a bottle etc

I really don't think its any more complicated than that

cheers
Dave
 
  • #6
I do understand that we hear the whistling of air because of the edges but don't we hear sound come from the bullet vibrating itself too or is that negligent? I know its hard to tell it just being a video but how loud (dbs) do you imagine that the whistling itself to be, or can I calculate it someway? Thanks for you help.
 
  • #7
luxun2 said:
Alrighty, well sound in my mind are the vibrations that propagate through air, water, and solids.
Yes, excellent.

luxun2 said:
...along with the Doppler effect.
Yes, I heard the Doppler too.

luxun2 said:
...but don't we hear sound come from the bullet vibrating itself too or is that negligent? I know its hard to tell it just being a video but how loud (dbs) do you imagine that the whistling itself to be, or can I calculate it someway? Thanks for you help.

I actually don't know (about the bolding part). But I will do something an experimentalist might had done - I will run a frequency analysis of the sound :-p. I'll post it here when I'm done. Oh, the wonders of internet...
 
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  • #8
Ok, I'm done. I downloaded the clip, run a noise reduction on it and cut out the part where the bullet can be heard going through the Doppler shift. This part was approx. 0,75 seconds long. Here's the result of the analysis (dB on the y-axis, frequency on the x-axis):

13140014683_83ce158df3_o.jpg


Now, regretfully I am a little too tired to think about this thing :smile:, but the frequency analysis shows basically frequency peaks which start at about 3200 Hz and end at about 800-900 Hz. I'm not sure what the 250 Hz peak is at the moment (i.e. if it is from the bullet). I can not give an approximation at the moment how loud the sound actually was (it depends on e.g. the microphone and recording level, and I'm also too tired to think clearly about it at the moment :biggrin:). Never mind, something for further discussion. I'll hopefully drop in here tomorrow.
 
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  • #9
luxun2 said:
I do understand that we hear the whistling of air because of the edges but don't we hear sound come from the bullet vibrating itself too or is that negligent? I know its hard to tell it just being a video but how loud (dbs) do you imagine that the whistling itself to be, or can I calculate it someway? Thanks for you help.

The edges would contribute to the all the frequencies heard, but have you also ever heard the sound of a bullet ricochet off a rock in the cowboy western movies. Being deformed, the bullet will now tumble in a chaotic fashion ( using chaotic here to mean you would have a difficult time determining how the bullet will be spinning ). The tumbling will produce a sound at a certain frequency and then add in all the other sounds from the jagged edges.
 
  • #10
Nice answers thanks for the help all.
 

FAQ: Why do objects whistle when falling? Like here.

Why do objects whistle when falling?

Objects whistle when falling due to the vibrations created by the air rushing past them. As an object accelerates towards the ground, it displaces air molecules which then collide with each other, creating a sound wave. This sound wave is perceived as a whistle.

Does the shape or size of an object affect the whistling sound it makes when falling?

Yes, the shape and size of an object can affect the whistling sound it makes when falling. Objects with a streamlined shape, such as a skydiver or a feather, will create a smoother and higher-pitched whistle compared to a larger, more irregularly shaped object like a rock or a book.

Why do some objects not whistle when falling?

Some objects may not whistle when falling because they are not able to displace enough air to create a sound wave. This could be due to their shape, size, or the speed at which they are falling. Additionally, some objects may not be perceived as whistling due to the limitations of our hearing range.

Can the whistling sound of an object falling be used to determine its speed?

Yes, the pitch of the whistling sound can provide some information about the speed of the falling object. As an object falls faster, the frequency of the sound waves increases, resulting in a higher-pitched whistle. However, other factors such as the shape and size of the object can also affect the pitch of the whistle, so it may not always be an accurate measure of speed.

Is there a difference in the whistling sound when an object falls through different mediums, such as air and water?

Yes, there is a difference in the whistling sound when an object falls through different mediums. This is because the density and composition of the medium can affect the vibrations and sound waves created by the falling object. For example, an object falling through water may produce a lower-pitched sound compared to the same object falling through air due to the differences in density and resistance.

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