Why Does Sound Propagate?

[3iMaJ]

That's a good question. I don't really know the answer.



I guess the closest I can say is that, user 3v0 asked about an object getting hotter as it's lifted up against gravity and I don't know the answer.



If you have three bricks, one on each level of shelving, the uppermost one has the most potential energy. If the three bricks, themselves, are examined, is that energy difference apparent in any measurable way? Does the energy only manifest itself by the way it acts when it moves (in other words, is it the environment that interacts with the brick as it falls or is lowered that makes the brick seem to have had more potential energy?



Unfortunately, perhaps, there's no shortage of nit picking that can be done with something like this. Can the heat in the brick convert some water to steam and if the steam does some work, is that the same as connecting the brick to the pulley? But, even there, does the upper shelf brick have the capacity to make the water hotter? Directly from its inherent heat or only if you sum it's heat and kinetic motion as it's lowered?

I'm not trying to nit pick, I'm trying to get you to be VERY precise and unambiguous about what you mean. If you want to talk about heat energy fine, and certainly there is some potentional energy to warm water (assuming that the water isn't in the same room at room temperature).

However, IF we're going to have this conversation then we need to be very precise and unambigous about how we define the different types of energy and what exactly those definitions mean, otherwise this conversation will be frustrating and a big waste of time as nothing will be accomplished.

Most of this thread is wrought with vaguety, everyone assumes that everyone knows what they mean when they say "energy" or "knetic energy" or "heat energy" or "work" or "pressure" etc. When in MOST cases those words mean different things to different people.

So BEFORE we continue this conversation we should first define energy, potentional energy, heat energy, kinetic energy etc. This might sound like a waste of time, but I assure you it will save pointless arguing about definitions of words later.

 

[crashsite]

Definition 101

I'm not trying to nit pick, I'm trying to get you to be VERY precise and unambiguous about what you mean.

You are not...but, I am and you very accurately state it as part of the problem.

I am seeing sound propagation as being propelled by, "heat". More specifically, as related to the motion of air molecules due to both ambient thermal erergy and the addition/subtraction of energy by some disturber.

So BEFORE we continue this conversation we should first define energy, potentional energy, heat energy, kinetic energy etc. This might sound like a waste of time, but I assure you it will save pointless arguing about definitions of words later.

I think that's an excellent idea.

Now, I could just ask, "What are a, b, c and d?" but, that would not be productive. But, if I venture to say what I think is happening, it gives others some specific meat to chew into. So, let me take a stab at, 'energy" and "heat energy".

Everything (that we can sense) in the universe is either some form of energy or nothing. Matter is just a highly concentrated form of energy and thereby has its own set of characteristice (such as being a gas, liquid, solid or plasma, etc.).

Exactly what "energy" is needs to be defined.

Matter is composed of atoms and atoms (almost always) arranged as molecules. Energy and its (shall we) say, "alter ego", matter, interact and freely exchange forms. That means that matter (the stuff we can deal with directly) can both absorb and release energy (radiently). It can also move it around within the matter (by conduction).

When energy is absorbed by matter it does so by making the molecules move faster and so, I guess, that is about as good a cursory definition of, "heat energy" as I can give in just a couple of paragraphs.

 

[j.friend]

Ok... interesting to see where this thread has gotten too...

The upshot of all that is that I don't know how gravity fits into the energy or heat picture.

We had a discussion about the role of gravity in buoyancy but, did not get into the heat issue of it. As a quick review, the question was:

If you have a helium filled balloon in the weightless environment of the ISS, what direction will it float to? What about if it's a brick?

In a gravitational field and in air, the balloon will float upward. The reason given is that there is more air pressure pushing the balloon up than is pushing it down. But, what if the "pressure" is actually, heat. What if the reason the balloon rises is because there is more or more vigorous molecular movement pushing on the bottom of the balloon (Newtonian action and reaction)?

As the medium becomes more dense, the balloon becomes even more buoyant. There are either heavier molecules in the medium or more of them.

Assuming that your theory is correct, which I personally do not believe, in the ISS the air pressure would be the same all around the brick or balloon. therefore their motion would be the same.

Ok the first thing here is that the balloon and both the brick will travel in the same direction or same manner within the ISS. The 'weightless' environment of the ISS is due to everything in the ISS falling at the same speed.

You can think of something falling of floating as being due to the relative force exerted on it due to gravity. For a Helium balloon in our environment, the reason that it floats is due to the average density of the comparative gases. it is a well known fact that gases take up roughly the same amount of space for the same number of particles at the same temperature.

try and imagine that each gas molecule is a tethering point, upon which a constant force is applied to to gravity(i.e. the force applied to each molucule is dependant on the molecules mass). The lighter particles therefore experience a lesser force i.e. in your helium balloon. This makes it 'float' in comarison to the heavier air. If you apply this to the brick model as well you can see why a brick falls so fast in air.

However when in orbit of a gravitational field, the acceleration to achieve the circular motion is supplied by the gravitational force. This means that the maxiumum force for everything within the ISS is being exerted to maintain the circular motion, meaning that everything seems weightless.

So ultimately I do believe that your brick and balloon would experience the same motion in the ISS, and it wouldnt particularaly 'float' anywhere unless you gave it a push in a certain direction.

In relation to defining the energies....

Energy - The capacity of a system to do work.

By this, if it has thermal energy, it is capable to do work in relation to exertion of heat. Likewise kinetic energy, it is capable to do work due to its motion.
etc....

Kinetic energy- the energy an object has due to its motion. Dependant on mass and velocity.

Potential energy- the energy stored within a system that can be released at a later point.

Work - the exertion of energy.

any of these are up for debate

 

[3v0]

F=ma

@j.friend, did you see the post were I used crashsite's physics to show how anti gravity works ?

We know things fall according for the force applied by gravity. f=ma

We know in atmosphere the helium balloon rises. The balloon rises because gravity is pulling with a greater force on the air around it. In effect gravity pulls air from above the balloon to below the balloon and forces the the balloon up.

One would have to ask why this would be any different in the ISS? Inside the space station f=ma still holds but a is zero because the space station is falling. No gravity, so the f=m*(zero),

But if there is not gravity...

3v0

 

[j.friend]

I must say that i did and it made my laugh quite a bit.

One thing I want to clarify however

One would have to ask why this would be any different in the ISS? Inside the space station f=ma still holds but a is zero because the space station is falling. No gravity, so the f=m*(zero),

there is still gravity acting on all the objects, however all the force provided by gravity is used to force the orbiting object into circular motion. The effective force of gravity on the objects within the ISS relative to each other is zero. This is why everything seems weightless.

The key to orbits... is seeing that the orbiting is always falling towards the earths surface, however the earths surface is falling away (curving) at the same rate that the orbiting object is falling at. Therefore weightlessness is only relative.

 

[3v0]

We are on the same page.

Yes to and thanks for

The effective force of gravity on the objects within the ISS relative to each other is zero.

I should have (and intended to) say
No effective gravity, so the f=m*(zero)

3v0

 

[crashsite]

We the people.....

We know in atmosphere the helium balloon rises. The balloon rises because gravity is pulling with a greater force on the air around it. In effect gravity pulls air from above the balloon to below the balloon and forces the the balloon up.

The only reason something ever moves is because there's more force being applied to one side of it than on the other. And, it's always the greater force that's doing the work.

The air outside the balloon knows nothing of the balloon but, it does have pressure. A key question is, "what is that pressure?". In a gross, mechanical sense, on earth it is the pressure caused by the sum of all the air above it (there's roughly 14.7 pounds of it for every square inch between the stratosphere and sea level).

At the molecular level, the air is a gas because there is enough heat in it to keep the molecules bouncing around in all three directions. If air were different molecules or if it has lost enough heat to no longer have enough energy to act like a gas, it might become a liquid. Okay, there's no might about it. It does becme a liquid.

Air pressure is really, heat. It's the energy of the molecules in motion; knocking about to keep them pushing each other apart and the force of that pushing is the pressure. And, that's why there's a direct relationship between heat and pressure in a gas.

Of course air molecules not only push against each other, they also push against anything that's adjacent to them. For example,.the skin of a balloon. The air is constantly trying to move the balloon.

Take the case of an air-filled balloon. You can tap the bottom of the balloon and it will rise up. But, it's heavier than the air around it (for two reasons). First, because it's the sum of the weights of the air and the latex of the balloon. Second, because the latex has an elasticity that needed to be overcome to blow the balloon up (in other words, the air in the balloon has more air pressure than that of the surrounding air).

But, the balloon doesn't just fall to the floor at a rate of 32 feet per second per second. It slowly sinks. Why? The balloon does have some buoyancy. It's difficult to imagine (at least for me it is), that there could be enough change of air pressure across the height of the balloon to significantly affect its buoyancy...but, there is. the air pushes up on the bottom of the balloon harder than it pushes down on the top.

But, what does it mean when you say that air is "pushing" on the balloon? It means that there is a force and a force implies energy and where's the energy in the air? Answer: it's in the heat that's moving the air molecules around.

I'm going to stop at this point to let you ponder these points and to think about how, if this is true, it will affect a helium filled balloon and also how it will affect a hot air balloon (there are some fairly significant differences between the two).

I'm sure some of you are thinking that that was sure "rambling". But, really it's just trying to put together some of the peices. Sort of a preamble to the actual explanation of why a helium balloon rises. What's more, there's more "preamble" that needs to be addressed. Sorry.

 

[crashsite]

f=ma, indeed...

Okay, you've shown that, in a mathematical equations, if you multiply something by zero the result is zero. But, it doesn't explain the concept of how it works.

 

[3v0]

Yet more nonsense

You posted 10 paragraphs and said next to nothing. Your verboseness on the subject tends to hid any nuggets of truth you arrive at rather then help support it. Most people get tired of the nonsense after a paragraph or two.

You may not like F=MA but you have yet to do more then babble about any of your concepts.

The entire bit about heat is pressure is questionable. If they were identical then all the pressure in our car tires would leak away as heat.

Firm up you own physics prior to attacking what works.

Okay, you've shown that, in a mathematical equations, if you multiply something by zero the result is zero. But, it doesn't explain the concept of how it works.

The formula beautifully quantifies the qualitative nature of gravity that we experience. You are correct that it does not explain why it works. But is does show how it acts.

How gravity acts is as much as you can show with Newtonian physics. Scientists are still searching for the theory of everything that will tie gravity and the other forces together.

3v0

 

[crashsite]

Defining moments...

In relation to defining the energies....

Energy - The capacity of a system to do work.

By this, if it has thermal energy, it is capable to do work in relation to exertion of heat. Likewise kinetic energy, it is capable to do work due to its motion.
etc....

I'm going to just ask a few clarifying questions.

Is it possible that "energy" can be defined as "mass in motion"? Some might invoke it as the conservation of matter and energy.

Kinetic energy- the energy an object has due to its motion. Dependant on mass and velocity.

By your definition, does that mean that any object that's above absolute zero automatically has, kinetic energy? Must you assume the gross case of an object that you can heft in your hand or does the definition also apply at the atomic level of molecular movements?

Potential energy- the energy stored within a system that can be released at a later point.

I'm glad you said, "system" rather than "object". But, this doesn't define potential energy. It just comments on it. what is it about that system that stores that energy?

Work - the exertion of energy.

I thought the classic definition of, "work" requires that something actually move. So, I'd ask two questions. First, is work being done when light shines on a wall (and pushes against it but, doesn't move it)? Second, if any object above absolute zero has thermal energy (moving molecules), is work being done all the time?

I hope we all can keep this moving forward and avoid getting into esoteric phenomena. I also hope that, in the back of our minds, we can keep the goal in sight of how this may all relate to how sound energy propagtes.

 

[3v0]

More problems

Second, if any object above absolute zero has thermal energy (moving molecules), is work being done all the time?

Two objects at absolute zero on a collision course will still display a lot of energy when the collide.

An object in orbit above the earth at absolute zero still possesses kinetic and potential energy.

EDIT:
The answer here is that we can talk about kinetic energy at two levels.

At the molecular level kinetic energy as you say the same thing as heat.

But at the object level, cars, rock, planets; kinetic energy is not related to heat in any way except for friction heating due to moment.

3v0

 

[crashsite]

Meat and Potatoes vs. Hot Air

You posted 10 paragraphs and said next to nothing. Your verboseness on the subject tends to hid any nuggets of truth you arrive at rather then help support it. Most people get tired of the nonsense after a paragraph or two.

Anybody can make a two sentence synopsis of a complex subject, throw in a couple of semi-related links and then rise up and beat their chest and pronounce the subject resolved.

I rather tend to like user, j_freind's approach of actually considering things and then making his own analysis. I don't always agree with him but, at least he provides enough detail to be able to properly disagree.

The entire bit about heat is pressure is questionable. If they were identical then all the pressure in our car tires would leak away as heat.

Actually, some of the pressure does leak away as heat (conversely, on the next hot day, or after a drive, it can also be put back...as heat).

Why doesn't all the pressure leak away as heat? Well, because, after pumping up the tire and some of the energy of compressing the air leaks away, the tire reaches an equilibrium where it's absorbing and radiating/conducting the same amount of heat and so the pressure also stabinlizes.

One of the points I have made is that the amount of change in the energy you typically put into matter is small compared to the amount of energy in it even at nominal temperatures. The use of a car tire is a good and practical way to demonstrate this (and even measure it).

You characterized my analyses as, "hot air". A very good point. Compressing the air heats it. Thanks for clarifying my position.

 

[crashsite]

The Tangent

Two objects at absolute zero on a collision course will still display a lot of energy when the collide.

An object in orbit above the earth at absolute zero still possesses kinetic and potential energy.

There are no objects in space at absolute zero. Okay, I suppose it's possible that there is a particle, somewhere in the universe, that has zero movement relative to the universe as a whole but, can' we ignore that little guy (who would only exist for the briefest of instants anyway)?.

If energy is mass in motion and that's heat....

And, here we go...zinging off on one of those crazy tangents that I hoped we could avoid....

 

[3v0]

You are again very very wrong

This goes to the rotten stinking core of you everything is heat theory. Not exactly a tangent.

There are no objects in space at absolute zero. Okay, I suppose it's possible that there is a particle, somewhere in the universe, that has zero movement relative to the universe as a whole but, can' we ignore that little guy (who would only exist for the briefest of instants anyway)?.

My use of absolute zero is theoretical.

Even at absolute zero an object consists of matter which can have potential or kinetic energy. Yes the molecules have stopped vibrating but they are still there.

You need to see the simple difference between linear motion of matter and heat.

3v0

 

[j.friend]

Take the case of an air-filled balloon. You can tap the bottom of the balloon and it will rise up. But, it's heavier than the air around it (for two reasons). First, because it's the sum of the weights of the air and the latex of the balloon. Second, because the latex has an elasticity that needed to be overcome to blow the balloon up (in other words, the air in the balloon has more air pressure than that of the surrounding air).

in the same way you can throw a rock in the air, and it is certainly heavier than the air around it. the resultant in the differing rates of falling is the relative force able to be applied by the object.

In the case of a brick, there is a lot of mass for a relatively small surface area. this means that it is able to exert a lot of force per unit area of surface to displace the surrounding air. This means that it is able to undergo a larger acceleration when moving through the air with the only force being applied by gravity.

When we compare the relative surface area and mass with an air filled balloon hopefully you can see that a much smaller force is able to be exerted per unit area in comparison to the brick.

the reason why this is a factor in the rate of falling is that in order to move through a medium (such as air in this case) a force needs to be applied to displace the particles of the medium that it is falling through. When i think about this I can see that if you had two objects of the same shape/surface area, yet with differing masses, the object with the greatest mass will fall much quicker than the object with less mass.

This effect can be seen in many cases, such as dropping a feather in comparison to say a marble. The feather has a comparitively massive surface area relative to its mass, whilst a marble has the smallest possible surface area for it's mass. If you managed to find a marble and a feather that weighed the same you would see that the feather would fall slower than the marble.

But, the balloon doesn't just fall to the floor at a rate of 32 feet per second per second. It slowly sinks. Why? The balloon does have some buoyancy. It's difficult to imagine (at least for me it is), that there could be enough change of air pressure across the height of the balloon to significantly affect its buoyancy...but, there is. the air pushes up on the bottom of the balloon harder than it pushes down on the top.

But, what does it mean when you say that air is "pushing" on the balloon? It means that there is a force and a force implies energy and where's the energy in the air? Answer: it's in the heat that's moving the air molecules around.

I struggle to fathom your theory that buoyancy of a balloon is due to differing air pressure. At a standard sea level pressure there is approximately 1kg of force per square cm. According to you theory the reason a balloon floats is due to there being a greater pressure below the balloon than above the balloon.

However if you consider place a helium-filled balloon on the ground, assume that the is effectively no air below it. That would mean that it would only have the 1kg/cm force pushing down on the balloon. Surely if the differing pressure was the reason that the balloon floated, the balloon would never leave the ground as their would be a much greater force acting down on the balloon.

I agree however that the pressure exerted on the balloon is related directly to the temperature of the surrounding air. However pressure cannot be simply explained as the heat of the particles. If this were so, the change in number of particles per unit cubic area would have no effect on the pressure. However pressure is also most clearer dependent on the number of particles per unit cubic area.

Therefore pressure can be considered as dependent on temperature, however it does not consist of temperature. This is in the same way that kinetic energy is dependent on velocity not consisting of velocity.

I'm going to just ask a few clarifying questions.

Is it possible that "energy" can be defined as "mass in motion"? Some might invoke it as the conservation of matter and energy.

Energy itself is not mass in motion, however a mass in motion can do work, exert an energy due to its motion. Energy is not defined as mass in motion however a mass in motion has energy

I thought the classic definition of, "work" requires that something actually move. So, I'd ask two questions. First, is work being done when light shines on a wall (and pushes against it but, doesn't move it)? Second, if any object above absolute zero has thermal energy (moving molecules), is work being done all the time?

I hope we all can keep this moving forward and avoid getting into esoteric phenomena. I also hope that, in the back of our minds, we can keep the goal in sight of how this may all relate to how sound energy propagtes.

Work is most certainly being done when a light is shone on a wall. Whilst work can be defined as the force exerted times the distance, work is also the expenditure (change) of energy over time.

For the second part, if the absolute zero particle is still moving (for this to be remotely possible it would have to be in a vacuum all by it's lonesome... I can explain why if necessary) It still has energy due to its motion. However if this energy remains constant there is no work being done.

Work, I believe, is simply the exertion of energy.

I'm glad you said, "system" rather than "object". But, this doesn't define potential energy. It just comments on it. what is it about that system that stores that energy?

The system allows energy to be stored in such a way that it is able to be released at a later point. I know this is pretty much exactly what I said before. lets look at some specifics.

gravitational potential is the potential energy of an object due to the gravitational force that can be exerted on it. I like my pencil up and it has gravitational potential energy, as when there is no restoring force (force upwards provided by my hand), It gains energy due to gravity.

In an elastic potential system, i stretch a rubber band with my hands. The forces between the molecules in the rubber band wish to be at the smallest possible energy level, i.e. molecules as close together such that the attraction betweens molecules is equal to the repulsion. When I have stretched the band, I have put energy into the system. I have lengthened the bonds between the molecules by putting extra energy into them. If my hands were not applying a force to keep it stretched, the molecules within the rubber band would attract each other back to the minimal energy configuration.

In fact when I do release the restoring force (my hands), the bonds attractions between the molecules pull the molecules back closer together. the extra energy that was in these bonds are released, partially in kinetic energy (the molecules moving back together, or perhaps a witty projectile) sound and loss of heat.

There are other sorts including chemical that I can go into if desired.

Actually, some of the pressure does leak away as heat (conversely, on the next hot day, or after a drive, it can also be put back...as heat).

Why doesn't all the pressure leak away as heat? Well, because, after pumping up the tire and some of the energy of compressing the air leaks away, the tire reaches an equilibrium where it's absorbing and radiating/conducting the same amount of heat and so the pressure also stabinlizes.

one last thing, i really don't like the way that you say pressure is leaked away. It's true that there is a change in pressure, but you can't just get a can of pressure and pump it into the system (well actually..... I suppose you can in a way....).

The reason for a change in pressure is the relative force applied to the tyre from the inside. This average force is dependent on the number of collisions of molecules with the tyre per second (partly dictated by the nu,ber of particles per unit cubic area) and then also the forve applied in each of these collisions (hey there is the heat energy of the particles)

As the particles lose or gain heat energy the pressure changes accordingly, also rather self explanitorily as the tyre loses or gains gaseous molecules the pressure changes. In this way you are correct in that a tyres reaches and equilibrium at which point the heat energy is the same.

anyways I have to go now... will discuss more later

 

[crashsite]

On the hunt....

My use of absolute zero is theoretical.

Even at absolute zero an object consists of matter which can have potential or kinetic energy. Yes the molecules have stopped vibrating but they are still there.

You need to see the simple difference between linear motion of matter and heat.

Let me zero in on this.

Sound does not propagate in an absolute zero environment (if it's even possible) and, I'm no expert on the topic. So, except to say that it's outside any conceivable scenario where sound is involved, I can't really say much (and what I can say is a guess).

But, the behavior of of heat in "normal" situations (as we'd be likely to encounter) are germain to the issue of sound propagation.

I'm trying to find a link that describes (in an amazingly simple way) the Bose-Einstein Condensate. I mention that here because there is a stage of cooling that uses lasers to literally make the environment colder by physically slowing down the atoms. I think I know how to find it...but, haven't actually located it yet.

You mention the molecules 'vibrating". I question whether they are vibrating (at least as a fundamental property of their thermal content).

 

[j.friend]

Let me zero in on this.

Sound does not propagate in an absolute zero environment (if it's even possible) and, I'm no expert on the topic. So, except to say that it's outside any conceivable scenario where sound is involved, I can't really say much (and what I can say is a guess).

How can you know whether or not sound can propagate (or alternatively not) in an absolute zero environment. Thus far, to the extent of my knowledge, we cannot create an absolute zero environment so we don't know if sound does propagate. please correct me if I am mistaken.

You mention the molecules 'vibrating". I question whether they are vibrating (at least as a fundamental property of their thermal content).

when referring to vibrating particles he is referring to their thermal content (i think)

absolute zero is achieved when there is no movement of the particle. This is clearly not achieved when something reaches a solid state, so it is thought that even in a solid state particles are vibrating within the structure.

It is in this way that the thermal energy of a particle is intrinsically linked to the kinetic energy of the particle. In gaseous form, if a particle has more thermal energy, it whizzes around faster. The reasons for the different states of matter is the relationship between the thermal/kinetic energy of the molecules in comparison to intermolecular bond strengths.

In part this also explains viscosity (although it is not the only factor). If you heat honey or treacle up, it gets runnier. This is because you are giving the molecules that make up the delectable sticky substance more energy, so the intermolecular forces cannot hold the molecules together as strong.

So overall when and if I refer to an atom/molecule vibrating it is in terms of its thermal energy. As when the thermal energy reaches zero the atom no longer vibrates.

I must admit it is a tricky concept to fathom when taking into account gaseous forms etc

 

[3v0]

Crash:
The energy is heat theory you base you sound theory upon can not account for the kinetic or potential energy contained by objects above absolute zero either.

Your brand of logic may work in religious circles. There is no place for in it physics.

If you do not want to be attacked for you logic at least try answering the questions directly put to you.

3v0

 

[j.friend]

was that directed at me or crashsite?

 

[3v0]

was that directed at me or crashsite?

I can not imagine how you could think it was directed at you ? But I have edited it to make that clear.