Can sound from any source create thrust?

AI Thread Summary
Sound waves can theoretically create thrust, but the effect is minimal and highly dependent on the geometry of the sound source and the surface it interacts with. While sound can induce vibrations that may result in a small net force, achieving significant thrust for propulsion is impractical due to inefficiencies in sound energy conversion. The discussion touches on concepts like acoustic levitation and ultrasonic drilling, emphasizing that while sound can manipulate small objects, scaling this to create a self-levitating vehicle poses significant challenges. The idea of using ultrasonic technology for lift is explored, but concerns about energy requirements and efficiency are raised. Overall, while sound can produce thrust, its practical application for significant propulsion remains limited.
sentil
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Can sound from any source create thrust??

hi there,

since I'm new to this forum, i don't know whether this the place to put up a question like this...!
if I'm wrong my sincere apologies

let me head to the topic now...

i wanted to whether the sound waves created form any source can develop thrust when the said source is held at the place of a strong surface that won't go crumble or distort with the thrust if any acting on the surface...

if I'm not clear with my query, just tell me i can explain further clearly.

Thanks
sentil
 
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I think the answer to you question is no. If the surface is small the sound of a normal source should move it back and forth, but it should not exert a net force (if it produces a constant tone). But the case is more complicated, because the airflow is involved. If you breath in and out rapidly at your hand, you will feel a blow but not a "suck", even though right at your mouth the two things should be the same. The reason is that the blowing is directed, while the sucking draws air from all directions. Similar things happen with a hand fan. So It depends a lot on the geometry of the speaker and the surface if a net force is exerted.
 


Actually yes. Finite amplitude effects and all that. Kind of in the same sense that propagating surface waves in water actually do produce a (small) net motion.
 


Thanks olivermsun for that clarification...but it didnt hepled me much...could you explain it much further...

looking forward to it..

sentil
 


JaredJames said:
There is a thread here somewhere, where a person used speakers to 'levitate' objects.

I'll see if I can dig it out.

EDIT: Here it is - https://www.physicsforums.com/showthread.php?p=2953959#post2953959

hey thanks...
you got it rite, i was indeed looking for a levitate mechanism with sound of some source...but the page you provide with me, was too technical that i couldn't make much out of that...

i would be much glad if you could crack it dwn for me...!

sentil
 


Thats how it feels to be at the bleeding edge, that's all there is, there isn't anymore, unless you make it.
 


If you hold a candle in front of a large loudspeaker and play a loud continuous tone through the speaker, the candle flame will lean away from the speaker - showing that there is a current of air in from the sides and out along the axis. It's not a large effect, though, but you could call it a thrust.
 


a thrust will be produced. but d energy of sound will not b much to observed as a thrust.
 
  • #10


vardhan_harsh said:
a thrust will be produced. but d energy of sound will not b much to observed as a thrust.

Thrust is thrust.

Whether or not it's usable is another issue.

Don't use text speak.
 
  • #11


Text speech sucks when you need to be accurate.
 
  • #12


sophiecentaur said:
If you hold a candle in front of a large loudspeaker and play a loud continuous tone through the speaker, the candle flame will lean away from the speaker - showing that there is a current of air in from the sides and out along the axis. It's not a large effect, though, but you could call it a thrust.

but sir, what if we could increase the amplitude of sound source..would that be enough...?

sir, i like to be precise here...

My idea is to build a device that has a sound producing tech at its bottom end, to create a lift, say few meters... and to maintain a constant height above the ground...
Initially i thought of electromagnetism for this but since it involves large outlays, i thought sound tech can help me in this quest...
n' I'm pretty sure that sound stream from speakers won't turn out to be a good one for the simply reason that, the said device will be put into deal with loads...

Sir, what if we use the tech behind infrasonic sounds that used to drill through rocks...? i guess the rock break into pieces due to some application of force ( infrasonic sound )created by the drill on the rock ( just another application of Newtons 3rd law too )...

what I'm thinking here is.. if we could increase the sq. area on which the infrasonic sound falls with the intensity not to break but to just enough to create a thrust on the ground that allowing the device to move upwards a few meters as i wanted... is this possible...?
 
  • #13


The loudspeaker is a very inefficient method for providing thrust.
The point is that sound is a vibration - a cyclic movement / displacement in different directions. What you want is movement in one direction( 'DC' sound !). The two are not really compatible. Why do you want to do it this way?
Infrasound to drill through rocks? Do you have a reference for this at all? Why not a Hammer?
 
  • #14
  • #15


OK. That's not thrust, though. Is it? It's vibration and very effective too.
 
  • #16


sophiecentaur said:
OK. That's not thrust, though. Is it? It's vibration and very effective too.
yes...but that is very effective since the said vibrations are concentrated against a small sq. area...is it...? but if could reduce the intensity..i.e; to increase the surface area on which the vibration falls on such a way, that the force created on the surface initially to break the rock...can it be used to create a force that can overcome the gravitational pull on a body in which it is mounted and in the opposite direction... so as to create an upward lift...? can it be termed as thrust...?

correct me if 'm wrong...!

Sentil
 
  • #17


This all depends on what you call thrust. You can push something with a pole. That's thrust. Many tools combine this with vibration to break up / drill a material. That's all so obvious that I can't believe it's what the OP was about.
I interpreted thrust in terms of propulsion. Sound is a longitudinal vibration. Half the time there is a force in the wrong direction! What exactly are we discussing?
 
  • #18


Accoustic levitation has been done for years for doing science experiments on liquids you are just inverting the process (http://science.howstuffworks.com/acoustic-levitation.htm)

It's very inefficient and we usually on use on small things like water droplets shown in the image above organize an angle or side force and you have propulsion in the strict sense like a "sound hovercraft" of sorts

Links:
http://en.wikipedia.org/wiki/Acoustic_levitation
http://io9.com/#!5523466/yes-you-can-levitate-objects-with-sound
 
Last edited by a moderator:
  • #19


sophiecentaur said:
This all depends on what you call thrust. You can push something with a pole. That's thrust. Many tools combine this with vibration to break up / drill a material. That's all so obvious that I can't believe it's what the OP was about.
I interpreted thrust in terms of propulsion. Sound is a longitudinal vibration. Half the time there is a force in the wrong direction! What exactly are we discussing?

sir, to be precise...i had in my mind, a device that can actually create a force [ from sound energy] that can, in fact act against the gravitational pull on the said device...!

i seriously apologize if i mislead you anywhere in our conversation...!
 
  • #20


If you mean a self-levitating vehicle then no chance. How loud do you imagine the engine would have to be?
 
  • #21
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  • #22


The link in parentheses does not work.

Are you aware of the concept of Efficiency? It is highly relevant here.
What is the point of being able to produce a tiny force if you need to be blasting Megawatts of sound (even ultrasound)?

Why do you quote ultrasonic drilling as an example of your idea? An ultrasonic drill just breaks stuff up by oscillations (alternating high and low pressure). How is that related to levitation?

We have already established that, on an experimental level, with small objects, levitation can be achieved. What you propose is different - about as possible as a solar powered helicopter!
 
  • #23


Leviation with sound is one thing, but can you propel things with sound waves in a certain direction. I'm thinking about an aerodynamic analogy of those bend rubber legs on hexbugs:

https://www.youtube.com/watch?v=EwrpBd_iiGc
 

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