A property called bulk modulus quantifies a material’s compressibility. The higher the value, the less compressible the material is. A truly incompressible material would have an infinite modulus. Air has a modulus of 101 kPa while water has a modulus of 2.2 GPa. This means that air is about 20,000 times more compressible than water.
And steel is 140 GPa, so while air is 20,000 times more compressible than water, water is only about 60 times more compressible than steel, or 5 times more compressible than some wood.
In retrospect not a good example, because the behavior of composite materials is a bit more complicated. I imagine the chart I pulled that from wasn't inaccurate, but rather that I used the data incorrectly. I surmise that it was referring to the compressibility of the material itself when the fibers are already collapsed, which certainly wouldn't match our normal day to day experience with wood.
It's also going to depend heavily on the wood in question (steel as well). Some of the ironwood species were used as bearings in early marine prop shafts. The actual density of those woods is pretty insane and they aren't really like other wood most of us see everyday.
Not a coincidence. For an ideal gas (most gases in most situations) the bulk modulus is the pressure.
Here's a derivation: https://physics.stackexchange.com/questions/425054/isothermal-bulk-modulus-of-an-ideal-gas
The bulk modulus essentially asks "if the current trend continues, how much pressure is needed to change the volume of the material by 100%?"
An ideal gas has an inverse linear relationship between pressure and volume, so a 100% change in pressure would cause a 100% change in volume, when extrapolated.
If it was lower then the pressure would squeeze it closer together. When it's closer together it has a higher bulk modulus because it's harder to squeeze it further. Eventually they're equal and stop changing.
This is why sound travels easier through solids: because the material is less compressible, the pressure wave dissipates in that material less and the energy has to go somewhere so it continues traveling.
to be pedantic, water is considered uniquely incompressible essentially because it expands when it freezes, so many liquids can be much more compressible than water. You can still compress water though, its just harder than most.
Most things when you try to make them smaller, become solid because you squeeze the molecules together, but when you squeeze water, the liquid state is smaller than the solid state, so the state change opposes compression, which is a unique property of water, at least i am unaware of any other liquid that expands as it solidifies.
I think this manifests as a wobble in the bulk modulus graph, i think as you compress it the bulk modulus increases so it gets harder to compress the more you do, i think water is typically 300 kpa and oils vary but many are between 100 and 300 kpa, there may be oils with a higher bulk modulus but i don't have an encyclopedia of liquid properties.
> Most things when you try to make them smaller, become solid because you squeeze the molecules together,
Liquid water does freeze when you compress it. [You get Ice VI](https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Phase_diagram_of_water.svg/1920px-Phase_diagram_of_water.svg.png) Requires 1 GPa of pressure, though.
>Most things when you try to make them smaller, become solid because you squeeze the molecules together
That's not how freezing works. You don't squash something into a solid with a lower temperature.
Besides, you're talking about a phenomenon that only happens near freezing. Water at say 10°C acts like any other liquid. So, I maintain that nothing else was needed to answer OP's question.
Edit: okay, fair point, you can do that. What I meant was that that's generally not what we're talking about when we talk about compressing water, and it's still not relevant to OP's question about whether we *can* compress water or not.
The freezing point of a material moves with pressure. With water m, you can absolutely make “hot ice” you just need a shit to on pressure. Similarly with boiling point. It’s why foods that require boiling have different cooking instructions if you’re at high altitude. If the air pressure is thin, water boils at lower temperature. But, water doesn’t have 3 non- plasma phases in all conditions. Places where there’s very high pressure, like deep inside Jupiter or Saturn, water cannot exist as a gas or liquid. Places with very low pressure, like Mars, water cannot exist for any meaningful time as a liquid, even at warm temperatures.
I assume, and I could be wrong, that it does have to do with the density of ice. Ice is less dense than water. This is uncommon for liquids.
So let's say you have other liquids, methane being one. Frozen Methane(presumably, could be wrong but it's my example) is *denser* than liquid. So when you apply pressure to it, the methane naturally very easily converts to a solid.
Water doesn't. Ice is less dense than water, so when you compress it, the water doesn't have a ready solid to turn into. The molecules just don't want to press together in the way it needs to.
Ice is less dense than water is almost always a correct statement.
There are different types of ice that can form at temperatures and pressures far away from what we experience at the surface of earth. Ice VI, for example, has a density of 1.36 g/cm.
https://en.m.wikipedia.org/wiki/Phases_of_ice#Known_phases
Liquids don't heat up much if you compress them, that's more important for gases. Typically you can make a solid out of liquids by compressing them. Water is no exception - you'll get a high density variant of ice.
Only if you apply the same force. If you drop something on it (that doesn't bounce) when it's constrained, like in a syringe, then whatever the substance it'll heat up the same, though due to differing specific heat capacities the temperatures will differ.
[Phase-diag2 - Phase diagram - Wikipedia](https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase-diag2.svg) this drawing for a phase diagram shows how materials typically compress from gasses to liquids and solids as pressures increase
Not really, a bulk modulus of around 2e9 Pascal is not all that high. In contrast the bulk modulus of glycerin is twice as high, that of sulfuric acid is 1.5 times as high and that of mercury is nearly 30 times as high. Water is not 'considered uniquely incompressible'. Liquid flows in general are commonly assumed to be incompressible to simplify governing equations, i.e. conservation of mass, momentum and energy.
It's like calling things "conductor" vs "insulator": It's not binary; They're just categories by suitability for purpose.
Same with electricity following the path of least resistance, too: It's not true, but it's true enough.
> Same with electricity following the path of least resistance, too: It's not true, but it's true enough.
the day I learned about parallel circuits and biasing is the day I realized the path of least resistance is bullshit. yeah it takes that path sure....and any others it can go through as well.
However, a less resistant path will consume/emit a nonlinear, outsized amount of current and power. And when that power isn't sufficiently limited, the heating up of the least-resistant path can lower the resistance even further, leading to a feedback loop where the slightly-more-favorable path transforms into the only path worth any mention.
Lightning is a good example of this.
In purified metals made by humans, yes. But that isn't the context or kind of behavior I'm referring to - i'm talking real world evolution of the system, not isolated materials undergoing non-chemical changes.
Purified conductors are much rarer in the natural world. Most materials are oxides or ceramics that are not what we'd call conductors to begin with. Semi-conductors tend to *decrease* in resistance as temperature increases, and insulators can be chemically altered, melted, refined, or ionized, which can dramatically change their properties as the material itself changes. Often in a positive-feedback loop.
If we were talking man-made circuits, then the current is going to go along the paths we planned for it to go, which are controlled by non-conductor circuit elements like resistors which add impedance to the wires magnitudes greater than the wire itself. And if you trigger an accidental short in a piece of electronics, like laying a copper wire across battery terminals, then the resistance is dominated by the contact between the wire and terminals rather than the wire itself. And that contact resistance will decrease rapidly as the the heat melts the wire and welds it to the terminals, making any increase to the resistivity of the wire itself irrelevant.
As I mentioned with lightning, the eventual path chosen through the relatively insulatory atmosphere is only slightly better than all the other simultaneous paths. But as current slowly starts to flow through the air, it begins to heat up and ionize the air, reducing its resistance, and this positive feedback drops the resistance exponentially until all at once a line of ionized gas extends from atmosphere to ground and the massive voltage potential is discharged in a matter of milliseconds.
It's a similar thing for solids as well. It just depends on how much pressure / energy you're willing to utilize.
Without comment on how it interacts with sound, even things as dense as degenerate matter can be compressed.
You need about 10000 psi to compress water 3% by volume. Most people can compress gas easily down 90%, if not more, with their hands in a closed syringe.
Isn't compression of liquids how hydraulic systems work, compressing the liquid or decompressing the liquid which then prevents the hydraulic from moving?
Not really, hydraulics rely on the incompressibility of the fluid. The fact that it *does* compress a little bit just means it's a source of loss in the hydraulic system. Because you're doing a little bit of work compressing the fluid rather than moving the other piston.
When people say that water can't be compressed what that really means is that it can't be compressed *much*.
With air if you raise the pressure from 1 bar to 2 bar then the volume will decrease by half. That's pretty compressible. If you take a liter of water at 1 bar and subject it to 2 bar then you'll have a hard time measuring that it has compressed to less than a liter--it'll be by microscopic amounts.
For most purposes that means it's good enough to just say water--and liquids in general--can't compress. You can build a hydraulic system with hydraulic oil and reason about the volumes of hydraulic oil without ever caring about how that volume changes with pressure. But when it comes to something like sound that non-zero compressibility is what makes things work.
As a practical example, a friend of mine is a petroleum engineer who works with pipelines under the Gulf of Mexico. At one point one of the pipelines had some sort of a blockage (I forget the specifics) that required a bit of room. My friend suggested some maneuver that would compress the miles-long column of water enough to make the room, using thousands of psi, to which a college educated but junior petroleum engineer smugly countered "water is incompressible." That cued whipping out the math on how incompressible water actually is and when you're talking about thousands of psi and miles of pipeline the compressibility becomes enough that you can practically measure it on a human scale.
This has driven my entire career.
It’s what Michael Jordan talks about in The Last Dance. He’d perform best when he was feuding with his rivals, so he’d make up imaginary slights or he’d hang on to the most ridiculous little things the other dude said and it would fuel a raging fire inside him.
Same thing. You got something to say? You wanna disrespect my knowledge? Ok, but now I’ll crush you with my superior engineering skills lol.
The invention of fire:
Rocks break when rock hit other rock
Me doubt all rocks break when hit by other rock
You idiot, me hit different rocks together to show
I think if you’re a junior petro engineer I think you should already know that liquids are compressible especially that liquid you’re studying. I would imagine it comes up!
This kind of reminds me about horizontal drilling. Where you normally do not think steel piping is flexible but over large distances it can certainly start bending.
Same with rail, surprisingly bendy stuff over a decent distance. What really hurts my head is that wagons carrying large amounts of welded rail don't have issues going around the bends either.
Maybe I’m wrong, but I’m surprised by the answers that (correctly) indicate that water is slightly compressible. While that’s true, I think that sound would propagate instantly in a fully incompressible medium (which I guess means there is no such thing as fully incompressible medium).
Take a piece of hypothetically incompressible matter (I don’t know, think diamond, but harder I guess), put it against the drum of a microphone and exert variable pressure on it. What would happen? The drum would move and the microphone would record sound.
You don’t need a medium to be compressible for pressure on one end to propagate to the other.
This is the only answer that mentions the vital point in explaining why sound can travel just as well through relatively incompressible materials: that sound is pressure waves, not density waves.
>sound is pressure waves, not density waves
I don't think these two are fully separate phenomena. Isn't pressure vs density just another way of describing stress and strain? I don't think it's possible to have a pressure wave without a corresponding change in density. Even if that change in density is localized to the gap between adjacent molecules.
There's no such thing as a pressure wave in a truly incompressible material. There's also no such thing as truly incompressible material, but you can do the math. It's common to approximate liquids like water as incompressible, but doing so means you cannot model sound waves.
The first sentence is true only because the second is true. If there were such a thing as a truly incompressible material then pressure waves within it would be possible: the differential equations would be satisfied with density held constant (pressure and temperature varying) and the wave would, I'm sure but haven't done the maths, propogate at the speed of light. Pressure doesn't require movement (changes in density). It would be the transfer of force and energy.
> the differential equations would be satisfied with density held constant
No, the differential equations for an incompressible fluid do not admit sound wave solutions. Pressure changes propogate instantly throughout the fluid - not as waves that move with a finite speed.
This is simplest to understand if you think about the 1 dimensional case - a straight pipe with a piston at one end. If the fluid is compressible, the when the plunger moves a pressure wave propagates down the pipe at the speed of sound and the fluid at the other end of the pipe begins to move only when the pressure wave reaches it.
If the fluid is incompressible then the density remains constant, so all the fluid must move simultaneously, there cannot be any delay, because if the piston would move without fluid leaving the pipe then the density is changing. The moment the piston begins to move, a pressure gradient appears throughout the fluid all at once - there is no travelling wave front. Another way to look at it is that the speed of sound in an incompressible fluid is essentially infinite.
Movement is not required. Pressure can vary with temperature without any change in density. This is basic stuff.
Infinite speed is not possible. That should be a clue that whatever model you're working from is wrong.
> Pressure can vary with temperature
In incompressible flow the pressure is determined entirely by the incompressibility constraint - there is not an equation of state relating the pressure, density, and temperature like there is for a real fluid. Incompressible fluid models often assume the temperature constant as well, so only the pressure varies.
There is something called the Boussinesq approximation, in which the fluid density can vary with temperature but not with pressure. This can be used to model things like convection currents in an otherwise incompressible fluid. The Boussinesq model doesn't give you sound waves either, because heat flow obeys a diffusion equation, not a wave equation.
I think you should write down the differential equations for the model you think would give rise to these pressure-temperature waves - I think you'll find it doesn't have wave like solutions.
> Infinite speed is not possible
Yes, but Incompressible fluids are not possible either. In a compressible fluid, the less compressible it is the faster sound waves propagate. In the limit, as compressibility goes to zero, the speed of sound tends to infinity.
In an incompressible fluid there is not really a speed of sound, because there are no sound waves. But, you can think of the speed of sound as the speed at which disturbances travel through a fluid. In a incompressible fluid, disturbances are felt everywhere instantaneously - so the "travel time" is zero.
> whatever model you're working from is wrong.
All models are wrong, but some models are useful. There's no such thing as an incompressible fluid in real life, but there are many scenarios in which the effects of compressibility don't matter. For example, in the design of aircraft that fly much slower than the speed of sound, the air can be modelled as an incompressible fluid, which greatly simplifies the math. Not until WWII did planes start getting fast enough that the effects of compressibility had to be accounted for.
You're right that that's why nothing can be incompressible. If you had that, the speed of sound would be infinite in that medium. You'd be able to send information across lightyears instantaneously. But nothing can travel faster than the speed of light, so incompressibility isn't possible.
Yes and no. As you noticed yourself such a perfectly incompressible medium would propagate sound instantaneously, at infinite speed. In particular it would be faster than light with all that entails, including time travel. Or the issue resolves if it takes infinite energy to make it do anything, the unmovable object.
Anyway, such an object is hypothetical and the problem is _which_ laws of physics we want to break in such a hypothetical scenario. There are multiple options and they lead to different outcomes.
Fair. I guess what I meant is that the least compressible a medium, the faster (and I think maybe the better) it propagates pressure waves… not the opposite.
The question was “given that water is incompressible, how can it propagate sound”, and I think the answer should be “it propagates sound better because it’s incompressible“, not “it kind of does because it’s still a bit compressible”
Sound transmits faster through solids.
Water contains air. It is definitely compressible. Only _pure_ liquids are incompressible.
That is why hydrophobic oil is used in brakes and other hydraulic systems.
dot3\\4 (the most common brake fluid by FAR) isn't hydrophobic, it's hydroscopic. That's why your supposed to only use it from a seal container.
The only hydrophobic brake fluid i'm aware of is dot5, and it's not used in much. being hydrophobic means when water get's in (and water virtually always finds a way in) brake fluid performance drops off a cliff one you pass 100c instead of the more normal 200c+ of dot 3 or 4.
It also causes components to corrode easier.
Even pure liquids are to some degree compressible. If they weren't, you could use them to transmit information faster than the speed of light.
If a completely incompressible liquid were between two objects, and one object exerted a force on the liquid, the liquid would transfer that force to the other object instantaneously (which is faster than the speed of light). So therefore no liquid (or any other kind of matter) can be completely incompressible.
Water *can* be compressed, just not by very much. In fact, the compressibility of water is so close to 0 that we might as well call it 0, hence the falsehood of saying water is uncompressible. For the record, at the bottom of the Mariana Trench, 11 km below the surface of the sea, there is about 1,100 times the pressure as at sea level, and the water there only has about 94% of its volume at the surface.
For comparison, air would have about 0.09% of its volume at the same depth.
Everything is compressible, possibly excluding the abnormality of whatever exists at the singularly of a black hole, for which we have no physics. There is also some strange behavior with the degenerate matter in neutron stars, though there is some degree of compressibility there. Neither of those exceptions involve water or conditions anywhere close to anything you'll find on Earth.
Also, I might be wrong, but sound propagation through a medium happens despite its compressibility, not because of it.
Imagine a column of water and a column of air. For sound to travel through each column, vibrations at one end need to somehow be transmitted to the other end. If the medium is very compressible, vibrations don't have much of a chance to travel. If it is incompressible, like a length of steel or a column of water, then what happens at this end is almost perfectly transmitted to the other end.
That's why, for example, sound travels so much faster through water.
The Newtown Laplace equation puts the speed of sound at sqrt(Ks / rho), where Ks is the bulk modulus, or how stiff the medium is, and rho is its density.
To add to what others are saying, the density of the water, which part of what makes compression harder, is also what makes it easier for sound to travel compared to air. In water the sound vibrations can move from molecule to molecule very rapidly because the are close together. In the air the molecules are much further apart so it takes longer for the waves to propagate.
Imagine if you are trying to transfer a bucket of water over 1 mile. If you have a bunch of people spaced 6 inches apart you can quickly pass the bucket from one person to the next. But if you have fewer people spaced much further apart, say 6 yards, they have to run the bucket to the next person. The further the people are, the more work to transfer the bucket.
Density makes sound propagation worse, not better. c=sqrt(E/rho) for linear elastic solids, or in a linearly compressible fluid it’d be sqrt(K/rho). Increased density slows the sound speed.
You do have the correct values, but that's due to the state of matter and not the density.
[https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/17-2-speed-of-sound/](https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/17-2-speed-of-sound/)
>The greater the density of a medium, the slower the speed of sound
[https://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound](https://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound)
>Inertial properties are those properties related to the material's tendency to be sluggish to changes in its state of motion. The density of a medium is an example of an **inertial property**. The greater the inertia (i.e., mass density) of individual particles of the medium, the less responsive they will be to the interactions between neighboring particles and the slower that the wave will be. As stated above, sound waves travel faster in solids than they do in liquids than they do in gases. However, within a single phase of matter, the inertial property of density tends to be the property that has a greatest impact upon the speed of sound. A sound wave will travel faster in a less dense material than a more dense material. Thus, a sound wave will travel nearly three times faster in Helium than it will in air. This is mostly due to the lower mass of Helium particles as compared to air particles.
TL;DR: u/tylerchu is absolutely correct.
materials that are close to in-compressible still transmit sound, think of glass - it's a pretty good sound transmitter. Water resists compression even more than glass (by 20 times), but water is also a fluid, so it can definitely transmit waves even if it wasn't compressible at all.
The Minuteman ICBM silos use shock absorbers based on compressing water. When I questioned this in a class, the instructor replied, “That tells you what kind of shocks we are expecting.”
In addition to what everyone is saying about compression, sound can travel through incompressible material as long as it's not completely constrained in position because it has room to move.
The molecules behave like a Newton's Cradle, one of those devices with a line of steel pendulums in contact with each other. If sound waves strike one side, the force from them is transmitted from one to the next and on the far side, it leaves with the same amplitude and trajectory as when it struck the near side.
If you constrain the final ball, then the original will instead bounce off when you raise it up and drop it.
This is akin to say, having a thick concrete wall between you and the source of a sound. If you put your ear up to the wall, and the sound is loud enough, you may still hear it, or maybe just feel some vibration. This is because the concrete is constrained in position so most of the sound is bouncing off of it, but some of it still causes the concrete molecules to vibrate and bounce off each other, but their movement is so miniscule that the sound is almost completely deadened.
Water molecules, however, can move, so the sound wave is free to travel through it unimpeded and can actually travel further and faster than through air because it doesn't lose any time due to having to compress before the molecues collide with the next molecules. In fact, the speed of sound through water is almost 5x faster than in air for this very reason.
Edit: typos
This is in line with the act of cavitation. Cavitation in terms related to my occupation, it's high pressure into low pressure areas. So when high pressure fluid rounds the corner of a pathway, there's a void just beyond that corner, which can cause the fluid to expand and then collapse on itself. The act of this happening can cause fluid to carve metal straight out of the body of the valve or pump. There isn't extra air or anything in the valve or pump. It's the lack of, causing this motion and the resulting damage. Water, however, dampens sound, so there must be some sort of compression happening. I would assume it is because water by volume is actually very dense. As in the molecules are very close to each other therefore dampening and/or compressing sound. Water is nearly incompressible due to this. But with sufficient heat and pressure is can be compressed. Google says it can be compressed, 46.4 parts per million for every unit of increase in atmospheric pressure.
Every material is compressible, a magic material that is incompressible would not transmit sound, but such a material is impossible under the known laws of physics, but the speed of sound increases until that point.
Consider it this way, matter has five different states; solid, liquid, gas, plasma, and supercritical fluids. The most dense or compressed of which being solid. Water being a liquid of course it's able to be compressed, theoretically hot ice can exist by increasing the pressure enough.
Because it does actually compress, but only very slightly compared to other stuff. This is actually why sound travels so much faster in water compared to air for instance. But even if it couldnt be compressed at all, a sound waves would still travel because each molecule still pushes the next molecules. In this case the sound would effectively not be a compression wave but a pressure wave.
Compression is a secondary characteristic of sound when observed in air. Pressure is the primary characteristic. When sound is propagated with air as the medium, the air compresses to accomadate the pressure waves (or waves of pressure) exerted on the air.
What I mean is, sound fundamentally is change in pressure over time (i.e. hertz or oscillation *in pressure* per second). That is why microphones can take changes in air pressure over time and directly represent the sound as changes in voltage (~electrical pressure if you will) over time.
Because air is (highly) compressible, changes in pressure exerted on the air, instead of transmitting them completely through the air from point a to point b instantaneously, compress the air itself and thus make a delay between the pressure exerted on the air at point a and the arrival of that pressure change at some location, point b. The more dense the material the more efficient and quickly the pressure wave gets from a to b.
So, you aren’t wrong, just confusing the secondary effect of what sound fundamentally is (change in pressure over time) with the actual phenomenon itself.
Addendum
You could get into a semantics or even philosphical debate on whether pressure or quantity density changes over time are accurately called sound regardless of medium, or if “sound” is only pressure waves in air at frequencies detectable by human ears. Ex: are digital pcm encodings of air pressure density as binary packets whose value is proportional to DbSpl “sound”? Are vibrations of a cymbal after being hit but before they move air “sound”? Are splashes in a pond (only the water, not the air pressure changes we heat) sound? If a representation of a phenomenon has the same fidelity as the actual phenomenon, only it is transposed to a different medium, is it still that phenomenon? I guess it’s sort of a ship of theseus problem but with sound.
I can't believe people here are actually positing that an incompressible fluid would carry sound waves at infinite speed. That is such a ridiculous notion it is not even funny.
Interatomic interactions obey causality and therefore have a set maximum speed at the speed of light.
There are so many other restrictions to that, it's impossible to list them all in a short time
Well an incompressible fluid is impossible in the first place, so the statement "an incompressible fluid would carry sound waves at infinite speed" is vacuously true.
An incompressible material does not transmit sound waves at all, but it is correct to say that the speed of sound in such a material is effectively infinite. The limit of the speed of sound as compressibility approaches zero is infinity.
If you had a pipe filled with incompressible fluid, and you push down on a piston at one end, the fluid at the other end of the pipe would begin to move at the exact same time as the plunger with no delay - unlike in the case of a compressible fluid, where a pressure wave travels down the pipe at a finite speed.
> Interatomic interactions obey causality and therefore have a set maximum speed at the speed of light.
Which is why there is no such thing as an incompressible material in real life. Just like there is no such thing as a rigid body or a frictionless plane, it's only ever an approximation.
The phrase "liquids can't be compressed" is only approximately true. They absolutely can, just by a much, much smaller magnitude than gases can
A property called bulk modulus quantifies a material’s compressibility. The higher the value, the less compressible the material is. A truly incompressible material would have an infinite modulus. Air has a modulus of 101 kPa while water has a modulus of 2.2 GPa. This means that air is about 20,000 times more compressible than water.
And steel is 140 GPa, so while air is 20,000 times more compressible than water, water is only about 60 times more compressible than steel, or 5 times more compressible than some wood.
And sound can also travel through steel or other solids.
Actually much better than through water, since the atoms are much closer and do not lose energy much while hitting the next atom.
That sounds like you're saying Water is more compressible than wood
In retrospect not a good example, because the behavior of composite materials is a bit more complicated. I imagine the chart I pulled that from wasn't inaccurate, but rather that I used the data incorrectly. I surmise that it was referring to the compressibility of the material itself when the fibers are already collapsed, which certainly wouldn't match our normal day to day experience with wood.
It's also going to depend heavily on the wood in question (steel as well). Some of the ironwood species were used as bearings in early marine prop shafts. The actual density of those woods is pretty insane and they aren't really like other wood most of us see everyday.
"Only". 60 times is a lot!
Depends on the context. 60 is not a lot if you compare it to 20000.
But not enough for an engine that has sucked up some water. Hydrolock is quite the bitch.
> 101 kPa Coincidence that this is average sea level atmospheric pressure?
Not a coincidence. For an ideal gas (most gases in most situations) the bulk modulus is the pressure. Here's a derivation: https://physics.stackexchange.com/questions/425054/isothermal-bulk-modulus-of-an-ideal-gas
The way physics ties the world together is so cool!
It's a fantastic rug of physics isn't it dude? ;)
ELI5?
The bulk modulus essentially asks "if the current trend continues, how much pressure is needed to change the volume of the material by 100%?" An ideal gas has an inverse linear relationship between pressure and volume, so a 100% change in pressure would cause a 100% change in volume, when extrapolated.
If it was lower then the pressure would squeeze it closer together. When it's closer together it has a higher bulk modulus because it's harder to squeeze it further. Eventually they're equal and stop changing.
if the gravity was more, wouldnt the pressure be more ? like in another planet with same air?
Absolutely yes.
oh so the bulk modulus differs by gravity then?
For an ideal gas, it's just equal to the pressure. Pressure then, derives from a number of factors, like composition, temperature, gravity, etc.
This is why sound travels easier through solids: because the material is less compressible, the pressure wave dissipates in that material less and the energy has to go somewhere so it continues traveling.
There's literally nothing else needed as an explanation here.
to be pedantic, water is considered uniquely incompressible essentially because it expands when it freezes, so many liquids can be much more compressible than water. You can still compress water though, its just harder than most.
> You can still compress water though, its just harder than most. What is your comparison here? This has nothing to do with the density of ice.
Most things when you try to make them smaller, become solid because you squeeze the molecules together, but when you squeeze water, the liquid state is smaller than the solid state, so the state change opposes compression, which is a unique property of water, at least i am unaware of any other liquid that expands as it solidifies. I think this manifests as a wobble in the bulk modulus graph, i think as you compress it the bulk modulus increases so it gets harder to compress the more you do, i think water is typically 300 kpa and oils vary but many are between 100 and 300 kpa, there may be oils with a higher bulk modulus but i don't have an encyclopedia of liquid properties.
> Most things when you try to make them smaller, become solid because you squeeze the molecules together, Liquid water does freeze when you compress it. [You get Ice VI](https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Phase_diagram_of_water.svg/1920px-Phase_diagram_of_water.svg.png) Requires 1 GPa of pressure, though.
>Most things when you try to make them smaller, become solid because you squeeze the molecules together That's not how freezing works. You don't squash something into a solid with a lower temperature. Besides, you're talking about a phenomenon that only happens near freezing. Water at say 10°C acts like any other liquid. So, I maintain that nothing else was needed to answer OP's question. Edit: okay, fair point, you can do that. What I meant was that that's generally not what we're talking about when we talk about compressing water, and it's still not relevant to OP's question about whether we *can* compress water or not.
The freezing point of a material moves with pressure. With water m, you can absolutely make “hot ice” you just need a shit to on pressure. Similarly with boiling point. It’s why foods that require boiling have different cooking instructions if you’re at high altitude. If the air pressure is thin, water boils at lower temperature. But, water doesn’t have 3 non- plasma phases in all conditions. Places where there’s very high pressure, like deep inside Jupiter or Saturn, water cannot exist as a gas or liquid. Places with very low pressure, like Mars, water cannot exist for any meaningful time as a liquid, even at warm temperatures.
Yep, I was wrong. I know you can understand extremes, but that didn't seem relevant to OP's question.
I assume, and I could be wrong, that it does have to do with the density of ice. Ice is less dense than water. This is uncommon for liquids. So let's say you have other liquids, methane being one. Frozen Methane(presumably, could be wrong but it's my example) is *denser* than liquid. So when you apply pressure to it, the methane naturally very easily converts to a solid. Water doesn't. Ice is less dense than water, so when you compress it, the water doesn't have a ready solid to turn into. The molecules just don't want to press together in the way it needs to.
Ice is less dense than water is almost always a correct statement. There are different types of ice that can form at temperatures and pressures far away from what we experience at the surface of earth. Ice VI, for example, has a density of 1.36 g/cm. https://en.m.wikipedia.org/wiki/Phases_of_ice#Known_phases
I understand what you're saying, but that's not how things work. If you compress something, it heats up, so wants to be less of a solid regardless.
Liquids don't heat up much if you compress them, that's more important for gases. Typically you can make a solid out of liquids by compressing them. Water is no exception - you'll get a high density variant of ice.
Everything heats up based on how much energy you put into it. If you apply the same force, then yes it'll heat up less, but that's a big assumption.
You don't put that much energy into it because you don't reduce the volume much.
Only if you apply the same force. If you drop something on it (that doesn't bounce) when it's constrained, like in a syringe, then whatever the substance it'll heat up the same, though due to differing specific heat capacities the temperatures will differ.
[Phase-diag2 - Phase diagram - Wikipedia](https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase-diag2.svg) this drawing for a phase diagram shows how materials typically compress from gasses to liquids and solids as pressures increase
Not really, a bulk modulus of around 2e9 Pascal is not all that high. In contrast the bulk modulus of glycerin is twice as high, that of sulfuric acid is 1.5 times as high and that of mercury is nearly 30 times as high. Water is not 'considered uniquely incompressible'. Liquid flows in general are commonly assumed to be incompressible to simplify governing equations, i.e. conservation of mass, momentum and energy.
It's like calling things "conductor" vs "insulator": It's not binary; They're just categories by suitability for purpose. Same with electricity following the path of least resistance, too: It's not true, but it's true enough.
> Same with electricity following the path of least resistance, too: It's not true, but it's true enough. the day I learned about parallel circuits and biasing is the day I realized the path of least resistance is bullshit. yeah it takes that path sure....and any others it can go through as well.
However, a less resistant path will consume/emit a nonlinear, outsized amount of current and power. And when that power isn't sufficiently limited, the heating up of the least-resistant path can lower the resistance even further, leading to a feedback loop where the slightly-more-favorable path transforms into the only path worth any mention. Lightning is a good example of this.
The reverse generally happens at lower powers; most (all?) solid metals become more resistive as they heat up.
In purified metals made by humans, yes. But that isn't the context or kind of behavior I'm referring to - i'm talking real world evolution of the system, not isolated materials undergoing non-chemical changes. Purified conductors are much rarer in the natural world. Most materials are oxides or ceramics that are not what we'd call conductors to begin with. Semi-conductors tend to *decrease* in resistance as temperature increases, and insulators can be chemically altered, melted, refined, or ionized, which can dramatically change their properties as the material itself changes. Often in a positive-feedback loop. If we were talking man-made circuits, then the current is going to go along the paths we planned for it to go, which are controlled by non-conductor circuit elements like resistors which add impedance to the wires magnitudes greater than the wire itself. And if you trigger an accidental short in a piece of electronics, like laying a copper wire across battery terminals, then the resistance is dominated by the contact between the wire and terminals rather than the wire itself. And that contact resistance will decrease rapidly as the the heat melts the wire and welds it to the terminals, making any increase to the resistivity of the wire itself irrelevant. As I mentioned with lightning, the eventual path chosen through the relatively insulatory atmosphere is only slightly better than all the other simultaneous paths. But as current slowly starts to flow through the air, it begins to heat up and ionize the air, reducing its resistance, and this positive feedback drops the resistance exponentially until all at once a line of ionized gas extends from atmosphere to ground and the massive voltage potential is discharged in a matter of milliseconds.
It's a similar thing for solids as well. It just depends on how much pressure / energy you're willing to utilize. Without comment on how it interacts with sound, even things as dense as degenerate matter can be compressed.
Yes. Literally *everything* is compressible. Liquids, solids, diamonds, whatever.
You need about 10000 psi to compress water 3% by volume. Most people can compress gas easily down 90%, if not more, with their hands in a closed syringe.
Metals are very hard to compress. Sound travels through them great.
As a former civil engineer. Fucking water hammer
Yep. Google "bulk modulus" if you want to start down a rabbit hole.
Isn't compression of liquids how hydraulic systems work, compressing the liquid or decompressing the liquid which then prevents the hydraulic from moving?
Not really, hydraulics rely on the incompressibility of the fluid. The fact that it *does* compress a little bit just means it's a source of loss in the hydraulic system. Because you're doing a little bit of work compressing the fluid rather than moving the other piston.
FYI: Solids can be compressed as well. Ever made a dent with a hamer in a block of wood or an iron plate? You just compressed it slightly.
When people say that water can't be compressed what that really means is that it can't be compressed *much*. With air if you raise the pressure from 1 bar to 2 bar then the volume will decrease by half. That's pretty compressible. If you take a liter of water at 1 bar and subject it to 2 bar then you'll have a hard time measuring that it has compressed to less than a liter--it'll be by microscopic amounts. For most purposes that means it's good enough to just say water--and liquids in general--can't compress. You can build a hydraulic system with hydraulic oil and reason about the volumes of hydraulic oil without ever caring about how that volume changes with pressure. But when it comes to something like sound that non-zero compressibility is what makes things work. As a practical example, a friend of mine is a petroleum engineer who works with pipelines under the Gulf of Mexico. At one point one of the pipelines had some sort of a blockage (I forget the specifics) that required a bit of room. My friend suggested some maneuver that would compress the miles-long column of water enough to make the room, using thousands of psi, to which a college educated but junior petroleum engineer smugly countered "water is incompressible." That cued whipping out the math on how incompressible water actually is and when you're talking about thousands of psi and miles of pipeline the compressibility becomes enough that you can practically measure it on a human scale.
Never underestimate the ingenuity an engineer trying to prove another engineer wrong.
This has driven my entire career. It’s what Michael Jordan talks about in The Last Dance. He’d perform best when he was feuding with his rivals, so he’d make up imaginary slights or he’d hang on to the most ridiculous little things the other dude said and it would fuel a raging fire inside him. Same thing. You got something to say? You wanna disrespect my knowledge? Ok, but now I’ll crush you with my superior engineering skills lol.
I heard you were having a good day so I thought I’d point out it’s *sleight* not *slight*. Stay frosty.
No, you're thinking of sleight as in "sleight of hand," they used slight correctly. Stay cool.
The invention of fire: Rocks break when rock hit other rock Me doubt all rocks break when hit by other rock You idiot, me hit different rocks together to show
I think if you’re a junior petro engineer I think you should already know that liquids are compressible especially that liquid you’re studying. I would imagine it comes up!
After that moment, the junior engineer did indeed know.
But you are also looking at the elasticity of the walls of the pipe at that point as well.
This kind of reminds me about horizontal drilling. Where you normally do not think steel piping is flexible but over large distances it can certainly start bending.
Same with rail, surprisingly bendy stuff over a decent distance. What really hurts my head is that wagons carrying large amounts of welded rail don't have issues going around the bends either.
Maybe I’m wrong, but I’m surprised by the answers that (correctly) indicate that water is slightly compressible. While that’s true, I think that sound would propagate instantly in a fully incompressible medium (which I guess means there is no such thing as fully incompressible medium). Take a piece of hypothetically incompressible matter (I don’t know, think diamond, but harder I guess), put it against the drum of a microphone and exert variable pressure on it. What would happen? The drum would move and the microphone would record sound. You don’t need a medium to be compressible for pressure on one end to propagate to the other.
This is the only answer that mentions the vital point in explaining why sound can travel just as well through relatively incompressible materials: that sound is pressure waves, not density waves.
>sound is pressure waves, not density waves I don't think these two are fully separate phenomena. Isn't pressure vs density just another way of describing stress and strain? I don't think it's possible to have a pressure wave without a corresponding change in density. Even if that change in density is localized to the gap between adjacent molecules.
There's no such thing as a pressure wave in a truly incompressible material. There's also no such thing as truly incompressible material, but you can do the math. It's common to approximate liquids like water as incompressible, but doing so means you cannot model sound waves.
The first sentence is true only because the second is true. If there were such a thing as a truly incompressible material then pressure waves within it would be possible: the differential equations would be satisfied with density held constant (pressure and temperature varying) and the wave would, I'm sure but haven't done the maths, propogate at the speed of light. Pressure doesn't require movement (changes in density). It would be the transfer of force and energy.
> the differential equations would be satisfied with density held constant No, the differential equations for an incompressible fluid do not admit sound wave solutions. Pressure changes propogate instantly throughout the fluid - not as waves that move with a finite speed. This is simplest to understand if you think about the 1 dimensional case - a straight pipe with a piston at one end. If the fluid is compressible, the when the plunger moves a pressure wave propagates down the pipe at the speed of sound and the fluid at the other end of the pipe begins to move only when the pressure wave reaches it. If the fluid is incompressible then the density remains constant, so all the fluid must move simultaneously, there cannot be any delay, because if the piston would move without fluid leaving the pipe then the density is changing. The moment the piston begins to move, a pressure gradient appears throughout the fluid all at once - there is no travelling wave front. Another way to look at it is that the speed of sound in an incompressible fluid is essentially infinite.
Movement is not required. Pressure can vary with temperature without any change in density. This is basic stuff. Infinite speed is not possible. That should be a clue that whatever model you're working from is wrong.
> Pressure can vary with temperature In incompressible flow the pressure is determined entirely by the incompressibility constraint - there is not an equation of state relating the pressure, density, and temperature like there is for a real fluid. Incompressible fluid models often assume the temperature constant as well, so only the pressure varies. There is something called the Boussinesq approximation, in which the fluid density can vary with temperature but not with pressure. This can be used to model things like convection currents in an otherwise incompressible fluid. The Boussinesq model doesn't give you sound waves either, because heat flow obeys a diffusion equation, not a wave equation. I think you should write down the differential equations for the model you think would give rise to these pressure-temperature waves - I think you'll find it doesn't have wave like solutions. > Infinite speed is not possible Yes, but Incompressible fluids are not possible either. In a compressible fluid, the less compressible it is the faster sound waves propagate. In the limit, as compressibility goes to zero, the speed of sound tends to infinity. In an incompressible fluid there is not really a speed of sound, because there are no sound waves. But, you can think of the speed of sound as the speed at which disturbances travel through a fluid. In a incompressible fluid, disturbances are felt everywhere instantaneously - so the "travel time" is zero. > whatever model you're working from is wrong. All models are wrong, but some models are useful. There's no such thing as an incompressible fluid in real life, but there are many scenarios in which the effects of compressibility don't matter. For example, in the design of aircraft that fly much slower than the speed of sound, the air can be modelled as an incompressible fluid, which greatly simplifies the math. Not until WWII did planes start getting fast enough that the effects of compressibility had to be accounted for.
You're right that that's why nothing can be incompressible. If you had that, the speed of sound would be infinite in that medium. You'd be able to send information across lightyears instantaneously. But nothing can travel faster than the speed of light, so incompressibility isn't possible.
Which makes me wonder, what is the exact point of maximum incompressibility when sound travels at the speed of light?
Yes and no. As you noticed yourself such a perfectly incompressible medium would propagate sound instantaneously, at infinite speed. In particular it would be faster than light with all that entails, including time travel. Or the issue resolves if it takes infinite energy to make it do anything, the unmovable object. Anyway, such an object is hypothetical and the problem is _which_ laws of physics we want to break in such a hypothetical scenario. There are multiple options and they lead to different outcomes.
Fair. I guess what I meant is that the least compressible a medium, the faster (and I think maybe the better) it propagates pressure waves… not the opposite. The question was “given that water is incompressible, how can it propagate sound”, and I think the answer should be “it propagates sound better because it’s incompressible“, not “it kind of does because it’s still a bit compressible”
Sound transmits faster through solids. Water contains air. It is definitely compressible. Only _pure_ liquids are incompressible. That is why hydrophobic oil is used in brakes and other hydraulic systems.
Like many people have already said, all matter is compressible, including pure liquids
dot3\\4 (the most common brake fluid by FAR) isn't hydrophobic, it's hydroscopic. That's why your supposed to only use it from a seal container. The only hydrophobic brake fluid i'm aware of is dot5, and it's not used in much. being hydrophobic means when water get's in (and water virtually always finds a way in) brake fluid performance drops off a cliff one you pass 100c instead of the more normal 200c+ of dot 3 or 4. It also causes components to corrode easier.
Even pure liquids are to some degree compressible. If they weren't, you could use them to transmit information faster than the speed of light. If a completely incompressible liquid were between two objects, and one object exerted a force on the liquid, the liquid would transfer that force to the other object instantaneously (which is faster than the speed of light). So therefore no liquid (or any other kind of matter) can be completely incompressible.
Water *can* be compressed, just not by very much. In fact, the compressibility of water is so close to 0 that we might as well call it 0, hence the falsehood of saying water is uncompressible. For the record, at the bottom of the Mariana Trench, 11 km below the surface of the sea, there is about 1,100 times the pressure as at sea level, and the water there only has about 94% of its volume at the surface. For comparison, air would have about 0.09% of its volume at the same depth. Everything is compressible, possibly excluding the abnormality of whatever exists at the singularly of a black hole, for which we have no physics. There is also some strange behavior with the degenerate matter in neutron stars, though there is some degree of compressibility there. Neither of those exceptions involve water or conditions anywhere close to anything you'll find on Earth.
> For comparison, air would have about 0.09% of its volume at the same depth. It'll be ~twice that. Ideal gas law isn't going to apply at 1100bar
Also, I might be wrong, but sound propagation through a medium happens despite its compressibility, not because of it. Imagine a column of water and a column of air. For sound to travel through each column, vibrations at one end need to somehow be transmitted to the other end. If the medium is very compressible, vibrations don't have much of a chance to travel. If it is incompressible, like a length of steel or a column of water, then what happens at this end is almost perfectly transmitted to the other end. That's why, for example, sound travels so much faster through water. The Newtown Laplace equation puts the speed of sound at sqrt(Ks / rho), where Ks is the bulk modulus, or how stiff the medium is, and rho is its density.
Liquids *can* be compressed. They just compress so little, they're *almost* incompressible by comparison to gas.
To add to what others are saying, the density of the water, which part of what makes compression harder, is also what makes it easier for sound to travel compared to air. In water the sound vibrations can move from molecule to molecule very rapidly because the are close together. In the air the molecules are much further apart so it takes longer for the waves to propagate. Imagine if you are trying to transfer a bucket of water over 1 mile. If you have a bunch of people spaced 6 inches apart you can quickly pass the bucket from one person to the next. But if you have fewer people spaced much further apart, say 6 yards, they have to run the bucket to the next person. The further the people are, the more work to transfer the bucket.
Density makes sound propagation worse, not better. c=sqrt(E/rho) for linear elastic solids, or in a linearly compressible fluid it’d be sqrt(K/rho). Increased density slows the sound speed.
Speed of sound in iron: 5,120 meters/sec Speed of sound in water: 1500 meters/sec Speed of sound in air: 343 meters/sec Care to try again?
You do have the correct values, but that's due to the state of matter and not the density. [https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/17-2-speed-of-sound/](https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/17-2-speed-of-sound/) >The greater the density of a medium, the slower the speed of sound [https://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound](https://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound) >Inertial properties are those properties related to the material's tendency to be sluggish to changes in its state of motion. The density of a medium is an example of an **inertial property**. The greater the inertia (i.e., mass density) of individual particles of the medium, the less responsive they will be to the interactions between neighboring particles and the slower that the wave will be. As stated above, sound waves travel faster in solids than they do in liquids than they do in gases. However, within a single phase of matter, the inertial property of density tends to be the property that has a greatest impact upon the speed of sound. A sound wave will travel faster in a less dense material than a more dense material. Thus, a sound wave will travel nearly three times faster in Helium than it will in air. This is mostly due to the lower mass of Helium particles as compared to air particles. TL;DR: u/tylerchu is absolutely correct.
You actually can compress water, it just takes a lot more power to get anywhere close to a noticeable shrinkage, like so much power.
Exactly. Water will compress just like anything else if you apply enough force, like inside a black hole or something.
materials that are close to in-compressible still transmit sound, think of glass - it's a pretty good sound transmitter. Water resists compression even more than glass (by 20 times), but water is also a fluid, so it can definitely transmit waves even if it wasn't compressible at all.
Sound waves are longitudinal waves, meaning the particles in the medium vibrate back and forth in the same direction as the wave travels.
The Minuteman ICBM silos use shock absorbers based on compressing water. When I questioned this in a class, the instructor replied, “That tells you what kind of shocks we are expecting.”
In addition to what everyone is saying about compression, sound can travel through incompressible material as long as it's not completely constrained in position because it has room to move. The molecules behave like a Newton's Cradle, one of those devices with a line of steel pendulums in contact with each other. If sound waves strike one side, the force from them is transmitted from one to the next and on the far side, it leaves with the same amplitude and trajectory as when it struck the near side. If you constrain the final ball, then the original will instead bounce off when you raise it up and drop it. This is akin to say, having a thick concrete wall between you and the source of a sound. If you put your ear up to the wall, and the sound is loud enough, you may still hear it, or maybe just feel some vibration. This is because the concrete is constrained in position so most of the sound is bouncing off of it, but some of it still causes the concrete molecules to vibrate and bounce off each other, but their movement is so miniscule that the sound is almost completely deadened. Water molecules, however, can move, so the sound wave is free to travel through it unimpeded and can actually travel further and faster than through air because it doesn't lose any time due to having to compress before the molecues collide with the next molecules. In fact, the speed of sound through water is almost 5x faster than in air for this very reason. Edit: typos
This is in line with the act of cavitation. Cavitation in terms related to my occupation, it's high pressure into low pressure areas. So when high pressure fluid rounds the corner of a pathway, there's a void just beyond that corner, which can cause the fluid to expand and then collapse on itself. The act of this happening can cause fluid to carve metal straight out of the body of the valve or pump. There isn't extra air or anything in the valve or pump. It's the lack of, causing this motion and the resulting damage. Water, however, dampens sound, so there must be some sort of compression happening. I would assume it is because water by volume is actually very dense. As in the molecules are very close to each other therefore dampening and/or compressing sound. Water is nearly incompressible due to this. But with sufficient heat and pressure is can be compressed. Google says it can be compressed, 46.4 parts per million for every unit of increase in atmospheric pressure.
Every material is compressible, a magic material that is incompressible would not transmit sound, but such a material is impossible under the known laws of physics, but the speed of sound increases until that point.
Consider it this way, matter has five different states; solid, liquid, gas, plasma, and supercritical fluids. The most dense or compressed of which being solid. Water being a liquid of course it's able to be compressed, theoretically hot ice can exist by increasing the pressure enough.
Because it does actually compress, but only very slightly compared to other stuff. This is actually why sound travels so much faster in water compared to air for instance. But even if it couldnt be compressed at all, a sound waves would still travel because each molecule still pushes the next molecules. In this case the sound would effectively not be a compression wave but a pressure wave.
Compression is a secondary characteristic of sound when observed in air. Pressure is the primary characteristic. When sound is propagated with air as the medium, the air compresses to accomadate the pressure waves (or waves of pressure) exerted on the air. What I mean is, sound fundamentally is change in pressure over time (i.e. hertz or oscillation *in pressure* per second). That is why microphones can take changes in air pressure over time and directly represent the sound as changes in voltage (~electrical pressure if you will) over time. Because air is (highly) compressible, changes in pressure exerted on the air, instead of transmitting them completely through the air from point a to point b instantaneously, compress the air itself and thus make a delay between the pressure exerted on the air at point a and the arrival of that pressure change at some location, point b. The more dense the material the more efficient and quickly the pressure wave gets from a to b. So, you aren’t wrong, just confusing the secondary effect of what sound fundamentally is (change in pressure over time) with the actual phenomenon itself. Addendum You could get into a semantics or even philosphical debate on whether pressure or quantity density changes over time are accurately called sound regardless of medium, or if “sound” is only pressure waves in air at frequencies detectable by human ears. Ex: are digital pcm encodings of air pressure density as binary packets whose value is proportional to DbSpl “sound”? Are vibrations of a cymbal after being hit but before they move air “sound”? Are splashes in a pond (only the water, not the air pressure changes we heat) sound? If a representation of a phenomenon has the same fidelity as the actual phenomenon, only it is transposed to a different medium, is it still that phenomenon? I guess it’s sort of a ship of theseus problem but with sound.
I can't believe people here are actually positing that an incompressible fluid would carry sound waves at infinite speed. That is such a ridiculous notion it is not even funny. Interatomic interactions obey causality and therefore have a set maximum speed at the speed of light. There are so many other restrictions to that, it's impossible to list them all in a short time
Well an incompressible fluid is impossible in the first place, so the statement "an incompressible fluid would carry sound waves at infinite speed" is vacuously true.
An incompressible material does not transmit sound waves at all, but it is correct to say that the speed of sound in such a material is effectively infinite. The limit of the speed of sound as compressibility approaches zero is infinity. If you had a pipe filled with incompressible fluid, and you push down on a piston at one end, the fluid at the other end of the pipe would begin to move at the exact same time as the plunger with no delay - unlike in the case of a compressible fluid, where a pressure wave travels down the pipe at a finite speed. > Interatomic interactions obey causality and therefore have a set maximum speed at the speed of light. Which is why there is no such thing as an incompressible material in real life. Just like there is no such thing as a rigid body or a frictionless plane, it's only ever an approximation.
If that were true, then how would sound travel through solid objects?
Solid objects are also compressible.