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So I heard about this thing on vsauce a while ago, where scientists use this thing called “acoustic levitation”. They use ultrasonic frequencies to levitate various substances, for use of studying their properties in an isolated environment.

But I had a thought: if sound can push against gravity and cause objects to levitate, could it possibly push against an object, sending it away from the source of the sound? To be more specific, could ultrasound speakers be installed in the ceiling of a spaceship, and push its occupants towards the floor, simulating gravity?

Would this work? And what would be the possible side effects on the human body?

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    $\begingroup$ Wikipedia can answer that: Nobody has made it work yet on masses larger than a few grams. So...ants. (I, for one, welcome our new insect overlords) Besides, it turns out to be really, really handy to efficiently use the entire habitable volume of a spacecraft. $\endgroup$ – user535733 May 14 at 20:58
  • $\begingroup$ Hey Cobbington, welcome to the site. We don't, by custom designate an accepted answer for 24 hours, as this may discourage other (better) answers, it's fine to withdraw and then re-award the bonus later. Oh and +1 for an interesting first question/post. $\endgroup$ – Don Qualm May 14 at 22:29
  • $\begingroup$ I wonder if the energies needed to levitate a person this way would first rip them apart... $\endgroup$ – BMF May 15 at 0:32
  • $\begingroup$ I don't imagine the medium and long term effects of exposure to constant ultrasonic impulses of this magnitude would be good. $\endgroup$ – StephenG May 15 at 21:19
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Gravity acts on every atom of the body equally. Sound pressure decreases with distance and can only act on the exterior of objects. This would result in someone's head experience more force than their feet. Plus the downward force would be applied to the parts of the body that face up -- tops of feet, shoulders, boobs, top of the head.

Assuming your speaker is a multitude of point sources, all very close together, and to produce a uniform force in one direction then if the sides of a person (left v. right or front v. back) didn't have constant and equal area then they would experience unequal forces as they moved about. And humans generally have more surface area in the back, then the front.

The long and the short is that I think your space explorers would have difficulty walking around without practice, and they'd have really bad headaches from the ultrasonic noise bombarding their heads. Unless they wore styrofoam hats to absorb the sounds waves, then everyone would make fun of them for looking like dorks.

I think your idea is good, but instead of sound maybe wind like from a laminar flow that sources from the ceiling and leaves through holes in the floor. Get the same effect without the headaches, and your hair has that just blown out look all the time.

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  • $\begingroup$ Don't drop your papers. $\endgroup$ – fredsbend May 15 at 3:22

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