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Sound waves transport a small amount of mass, according to theory

physics.aps.org

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Re: Sound waves transport a small amount of mass, according to theory

#31

Post by petters »

dmurray wrote: post #29
dschuetz wrote: post #23

In fact, sound waves literally means moving matter ! Transporting mass along the wave propagation is a whole different thing. It depends on the matter that is moving/vibrating. While the propagation of kinetic energy through a medium cannot have mass, the mean mass transport through a closed surface should equal zero. However, if they've discovered that it, in fact, isn't - then it's a big deal.

Sound waves are often compared to water waves in this way. The water just moves up and down, and the horizontal movement is (mostly) an illusion. But everyone knows intuitively that the water is moving horizontally at least a little bit. Some ocean water gets left on the beach or the boardwalk, or perhaps your toy or ball gets swept out to sea on the waves. Is this the right analogy, or are they talking about somethi…

The water moves in circles/ellipses.

Re: Sound waves transport a small amount of mass, according to theory

#32

Post by Majromax »

petters wrote: post #31
dmurray wrote: post #29

Earlier quoted context omitted.

Sound waves are often compared to water waves in this way. The water just moves up and down, and the horizontal movement is (mostly) an illusion. But everyone knows intuitively that the water is moving horizontally at least a little bit. Some ocean water gets left on the beach or the boardwalk, or perhaps your toy or ball gets swept out to sea on the waves. Is this the right analogy, or are they talking about somethi…

The water moves in circles/ellipses.

Not in closed circles/ellipses. With finite wave amplitudes, a fluid parcel in wave motion experiences Stokes Drift (https://en.wikipedia.org/wiki/Stokes_drift).

In water, this effect arises because the fluid is deeper at the crest of the wave than at the trough, and wave velocities are faster in deeper water. The fluid parcel moves up -> forwards quickly -> down -> backwards more slowly.

I'm curious about whether the researchers here have demonstrated a similar effect for sound waves. Pressure waves have similar dynamics (with faster particle movement at lower pressures), and the researchers mention that this is a finite-amplitude effect.

Re: Sound waves transport a small amount of mass, according to theory

#33

Post by hwillis »

ricardobeat wrote: post #26

If this negative mass measurement turns out correct, does it mean that a powerful enough sound wave at a frequency outside hearing range could be the answer to the anti-gravity belt? Disclaimer: I have no idea what I’m talking about.

> The new calculation indicates that for ordinary sound waves in most materials, the mass carried is equal to the sound wave energy multiplied by a factor that depends on the speed of sound and the medium’s mass density.

Since the effect is proportional to the density of the medium, you can't get actual antigravity. The mass is always positive. It can just be lighter than the other matter around it.

Practically speaking, you definitely can't use this for levitation or anything. This is E=mc^2 stuff; you need far more energy than conventional levitation would take. The energy in normal sound waves is very low, so high energy sound waves are very destructive.

For reference, the reference level sound intensity is 1 picowatt per square meter. That's zero decibels, the human audible threshold or the quietest sound we can hear under ideal conditions. A conversation is ~60 decibels, or 1 microwatt/m^2. Hearing damage comes at >90 dB or 1 milliwatt/m^2. >140 dB is quite painful, but it's only 100 watts/m^2. A household extension cord can carry about a kilowatt in less than a square centimeter- millions of times more power.

Re: Sound waves transport a small amount of mass, according to theory

#34

Post by 725686 »

ricardobeat wrote: post #26

If this negative mass measurement turns out correct, does it mean that a powerful enough sound wave at a frequency outside hearing range could be the answer to the anti-gravity belt? Disclaimer: I have no idea what I’m talking about.

Your disclaimer just put a smile in my face.

Re: Sound waves transport a small amount of mass, according to theory

#35

Post by stevespang »

Do I detect a source of anti-gravity . . . .

. . ."The new calculation indicates that for ordinary sound waves in most materials, the mass carried is equal to the sound wave energy multiplied by a factor that depends on the speed of sound and the medium’s mass density. And the mass carried by sound waves turns out to be negative. It is a depletion of mass, rather an addition of mass. So sound waves in a gravitational field should float upward somewhat, like any buoyant object in wate".

Re: Sound waves transport a small amount of mass, according to theory

#36

Post by jerf »

tranchms wrote: post #9

I was on a plane today thinking about recent research that uses vibrational/waves to interact with objects. Researchers can suspend and manipulate objects with these waves. I was thinking, why isn’t it possible to use this technology to create levitating objects or vehicles??? Like UFO type flight. Just attach powerful emitters around the craft. This article makes me think this might be possible. F= m*a If waves poss…

"I was thinking, why isn’t it possible to use this technology to create levitating objects or vehicles???"

It can, at least if we squint a bit. There is a clear mathematical relationship with all the various bits involved. Compute the amount of energy required to create the amount of sound to levitate, say, something with the mass of a car.

You'll compute an amount of energy sufficient to destroy any conceivable emitter and any object it is targeted at. My intuitive guess is that you'll actually require an amplitude of sound that isn't sound anymore; there's actually a maximum volume that sound can have, because the bottom of the wave can only go to zero pressure. It can't go past vacuum.

Also, I'd have to think about it a bit more, but I believe it would require the emitter to be separate from the thing being levitated... I think trying to self-levitate with a sound emitter would be the mathematical equivalent of trying to fly by pulling up on your hair.

So don't think full-sized UFOs dapperly zipping about with discreet little "blip blip blip" sounds in the distance... think a train car running underneath a levitating car, with a speaker giving off energy comparable to continuously-exploding bunker-buster bombs, if not nuclear bombs.

Definitely better off with a helicopter.

There is a reason all the things you've seen lifted are little bits of styrofoam and ping pong balls.

Re: Sound waves transport a small amount of mass, according to theory

#37

Post by bshell »

ricardobeat wrote: post #26

If this negative mass measurement turns out correct, does it mean that a powerful enough sound wave at a frequency outside hearing range could be the answer to the anti-gravity belt? Disclaimer: I have no idea what I’m talking about.

If Xmen taught me anything it is that this is old news
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