A Helium Balloon

[Guest]

I know I'm missing something really fundamental.  But I have mostly dealt with solids and liquids.  I haven't dealt with gases in so long, I can't put my finger on it.

 

My daughter asked me, "Does a helium balloon go up because of gravity?  How would gravity make something go up?"

 

I actually had to give this some thought.  I knew it was due to air pressure and buoyancy.  But clearly gravity played a role.  But I never considered the paradox that gravity actually pushed something away.

 

So I broke it down.  What pushes something is a force.  There are only four fundamental forces.  It certainly wasn't electromagnetic.  Nuclear forces are obviously not involved.  So it must be gravity.  I reasoned out the path from gravity to flowing of fluids to buoyancy.  Thus, YES, it is fundamentally gravity, but it is a few steps away.

 

But then I realized that with liquids, the pressure of the liquid doesn't really enter into the equation.  But with gasses, air pressure is absolutely involved.  Well, what causes air pressure to increase?  Temperature.  That is caused by an increase in kinetic energy.  Then I remembered there is a link between kinetic energy and something.  That is where I broke down.

 

What am I missing?  Is there a connection to the nuclear forces in a small degree/

[Vort]

Air pressure is not directly involved. The pressure inside a helium balloon is actually slightly higher than that of the surrounding atmosphere. Rather, the important characteristic is density. The helium balloon is less dense than the surrounding air. This is because the helium molecules (atoms) themselves are far less dense than the mostly nitrogen and oxygen molecules surrounding them -- just over a fourth as heavy, in fact, while occupying more or less the same volume*.

 

But why doesn't the gas just spread out and become infinitesimally dense? With a balloon, the reason is obvious -- the balloon itself holds the gas in its shape. But with the atmosphere, the reason is a little more subtle: Gravity holds the atmosphere in place**. It is the force of attraction due to gravity that is ultimately responsible for the earth's atmosphere even existing and having any measurable density and pressure.

 

*The important thing with gases is not the actual volume of the molecules themselves, though helium is a rather large atom and might almost occupy as much space as the two-atom molecules of oxygen and nitrogen. Rather, the imporant thing is how much average volume each moving gas molecule takes up with its motion. To a pretty high degree, this is the same with almost all gases, which is why we can use the so-called Ideal Gas Law even though none of the gases is truly ideal.

 

**I remember one of my children (junior high or maybe high school age) once was given a thought experiment during a science class regarding what would happen if gravity "turned off" for one minute. Most of his classmates talked about how fun it would be to float around and "fly" or such things. My literal-minded son spoke up and said that everyone would suffocate almost immediately, because all of our atmosphere (being under pressure) would explosively leave the surface of the earth as soon as gravity "turned off". I laughed when he told me about that, then reminded him that the earth's rock volume itself is under tremendous pressure, and if gravity were to vanish, the earth itself would literally explode.

[Guest]

Well, I talked it over with my daughter and discovered my error.

 

Vort,

 

Actually, pressure/density/temperature are all related via the ideal gas law.  I was focusing on the temperature, but I realized that under conditions of equilibrium the balloon would have the same temperature as the surrounding air.  So, it would only make a difference during the phase of non-equalized conditions.

 

Once equilibrium is reached, only gravity is the main driving force.  That much we had already determined and you have concurred.

 

Now, if we can separate it from the original question (the balloon example) here's the question.  

 

1) When an air molecule has energy put into it, it turns into kinetic energy.  

2) I did not understand it to be an increase in the electrons, protons, or neutrons.

3) This energy is stored in the nuclear forces.  But is it the strong nuclear force or the weak nuclear force?  Or both?

Edited November 6, 2015 by Guest

[Blackmarch]

I know I'm missing something really fundamental.  But I have mostly dealt with solids and liquids.  I haven't dealt with gases in so long, I can't put my finger on it.

 

My daughter asked me, "Does a helium balloon go up because of gravity?  How would gravity make something go up?"

 

I actually had to give this some thought.  I knew it was due to air pressure and buoyancy.  But clearly gravity played a role.  But I never considered the paradox that gravity actually pushed something away.

 

So I broke it down.  What pushes something is a force.  There are only four fundamental forces.  It certainly wasn't electromagnetic.  Nuclear forces are obviously not involved.  So it must be gravity.  I reasoned out the path from gravity to flowing of fluids to buoyancy.  Thus, YES, it is fundamentally gravity, but it is a few steps away.

 

But then I realized that with liquids, the pressure of the liquid doesn't really enter into the equation.  But with gasses, air pressure is absolutely involved.  Well, what causes air pressure to increase?  Temperature.  That is caused by an increase in kinetic energy.  Then I remembered there is a link between kinetic energy and something.  That is where I broke down.

 

What am I missing?  Is there a connection to the nuclear forces in a small degree/

gravity pulls the denser gas down which forces the less dense gas up. same with liquids (why cold goes down and hot goes up)

[Vort]

Now, if we can separate it from the original question (the balloon example) here's the question.  

 

1) When an air molecule has energy put into it, it turns into kinetic energy.  

2) I did not understand it to be an increase in the electrons, protons, or neutrons.

3) This energy is stored in the nuclear forces.  But is it the strong nuclear force or the weak nuclear force?  Or both?

 

I'll respond as best I can, but I think the basic answer is: Energy and force are two entirely separate (though perhaps related) things. Energy is not "stored" in force.

 

1) Correct. When you put energy into a group of atoms or molecules of gas, two things will change:

1. The average speed of the gas molecules will increase; that is, the individual molecules will move around faster.
2. In all but monatomic gases (such as helium), the molecules on average will rotate faster.

Both of these manifest as an increase in temperature. So when you add energy to a gas (i.e. heat it up), the average kinetic energy of the gas molecules increases (i.e. it gets hot).

 

2) Correct. The number of fundamental particles doesn't change, just their average kinetic energy.

 

3) The energy isn't "stored" in any fundamental force. Rather, the energy is contained in the actual motion itself of the particles.

[Guest]

3) The energy isn't "stored" in any fundamental force. Rather, the energy is contained in the actual motion itself of the particles.

 

This is where I believe you are incorrect.  The energy is stored.  And it is converted into mass.  But in the circumstance we're talking about, it is an almost infinitesimal amount of mass.

 

In order for the molecules to increase in velocity, they have to be subject to acceleration.  That requires energy.  That energy goes somewhere.  And it isn't just the motion of the particles.

[Guest]

gravity pulls the denser gas down which forces the less dense gas up. same with liquids (why cold goes down and hot goes up)

 

There is more detail to that. 

 

From an entropic analysis, we have some motion from each particle.  Where we have more total motion (near the denser area) lighter particles will be pushed away to an area of lesser total motion (less dense atmosphere) which happens to be farther away from the center of the gravity well.

[Blackmarch]

There is more detail to that. 

 

From an entropic analysis, we have some motion from each particle.  Where we have more total motion (near the denser area) lighter particles will be pushed away to an area of lesser total motion (less dense atmosphere) which happens to be farther away from the center of the gravity well.

of course- an easy way to explain it the cooler molecules vibrate less so they take up less space and bounce off of other molecules less than warmer ones which will cause a seperation similar to if you had a jar mixed with a combination of nuts that were either large or small and shook it for awhile- eventually the larger ones end up on top and the smaller ones on bottom

[Guest]

OK.  For anyone interested, I found the answer.

 

Gluons.  The additional kinetic energy is converted into mass via gluons.

 

As energy is added to a mass, the energy is converted to mass via special relativity in the form of gluons.

[Vort]

Carb, I don't care to have an argument. But kinetic energy is not "converted" into "gluons", which are the hypothetical (more like virtual) particles that are supposed to mediate gravitational interaction. Where did you get the idea that energy of motion is somehow converted into gluons?

[Guest]

Well,

 

I'll first take a step back because I got the impression from a previous post that you did not understand that adding energy into an object added mass to the object.

 

Do you understand that principle?  -- Special relativity?

[Vort]

Well,

 

I'll first take a step back because I got the impression from a previous post that you did not understand that adding energy into an object added mass to the object.

 

Do you understand that principle?  -- Special relativity?

 

Yes, I understand special relativity pretty well. I also understand the basics of general relativity, though I never actually took an upper-level or grad course in gravitation. Have you studies physics?

[LeSellers]

The important thing with gases is not the actual volume of the molecules themselves, though helium is a rather large atom and might almost occupy as much space as the two-atom molecules of oxygen and nitrogen. Rather, the important thing is how much average volume each moving gas molecule takes up with its motion. To a pretty high degree, this is the same with almost all gases, which is why we can use the so-called Ideal Gas Law even though none of the gases is truly ideal.

Sorry, Vort. Helium is a very small molecule. One He atom is two protons and two electrons. The electrons completely fill the ring, so it takes only one atom to make a molecule. Also, being a "noble" gas, it is wholly non-reactive with any other atoms, so there are no helium compounds.

A helium balloon is not filled with 100% helium, most of the gas inside is air. Helium is very much "lighter" than air, so it only takes a small proportion of He to displace the weight of the balloon. The air is the same weight (for all practical purposes) as the air around the balloon, so it takes almost no part in the question.

A helium balloon rises in air because, as you said, it is less dense that the air around it. The weight of the air that would be in the place of the balloon is greater than the weight of the balloon, the air and the helium in it. It goes down, under the force of gravity. This forces the balloon up, but there was air there, too. So this "new" air, also being heavier, goes down, and the balloon takes its place. The process is endless (until a ceiling or some other denser matter "gets in the way").

I think we may say that the force of gravity drives it, but that the proximate cause of a He balloon's rising is the density differential, which does not answer Carborendum's question, since there are but four Physical forces. He wants it defined in terms of one (or more) of those.

Lehi

Edited November 20, 2015 by LeSellers

[Vort]

 

Sorry, Vort. Helium is a very small molecule.

 

You are right about this. I wasn't thinking when I wrote that helium was a "large" molecule. Like the other monatomic noble gases, it is quite small, tpyically the smallest of their period. (Helium's period consists of itself and hydrogen, which is by far the smallest atom, so helium is an anomaly in that it is actually the largest of its period. But still very small, smaller than any other atom except hydrogen.)

 

But the rest of what I wrote is correct.

 

A helium balloon rises in air because, as you said, it is less dense that the air around it. The weight of the air that would be in the place of the balloon is greater than the weight of the balloon, the air and the helium in it. It goes down, under the force of gravity. This ofrces the balloon up, but there was air there, too. So this "new" air, also being heavier, goes down, and the balloon takes its place. The process is endless (until a ceiling or some other denser matter "gets in the way").

I think we may say that the force of gravity drives it, but that the proximate cause of a He balloon's rising is the density differential, which does not answer Carborendum's question, since there are but four Physical forces. He wans it defined in terms of one (or more) of those.

 

No other answer is possible. The density differential does not "drive" the balloon rising. Suppose, for example, the helium balloon were in the space station in orbit around the earth. The volume of the balloon would still be significantly less dense than the air in the space station. Would the balloon then "float" to the "top" of the space station? Of course not. It would just hang there, wherever it was placed. It is the pull of gravity, which pulls harder on the (denser) air molecules than on the (less dense) helium molecules, that drives the balloon's rise.

[Guest]

I have.

 

What I was referring to is that as an object is accelerated, it gains mass.  But that mass has to come from somewhere.  It is the energy that it takes to accelerate it.  The energy input = K.E. which can be measured in joules.  But the number of joules can then be measured in terms of mass.  

 

Obviously for non relativistic speeds, the mass increase is negligible for most practical purposes.  But children ask questions.  I remember enough that there is an answer.  I just forgot a lot more than I care to admit sometimes.

 

I'm still not certain about the gluons.  But that is the best I can remember.  I'm just getting a little too old, and been away from it too long.  But now I'm trying to teach my kids stuff and they have the most detailed questions.  Yes, my 14 y.o. is asking questions that require relativity to answer.  And my Google-o-city rating is in the adept range.  But I just don't have time to get the information I need.  I was hoping someone had a quick answer that I could say -- Oh! Yah!  That was it.

 

So, off to consult the oracles of Google.

[cdowis]

Here is a helium balloon in the news

 

http://www.dailymail.co.uk/sciencetech/article-3326046/Lockheed-s-airship-gets-green-light-approves-massive-hybrid-vehicle-launch-2018.html

[Vort]

Here is a helium balloon in the news

 

http://www.dailymail.co.uk/sciencetech/article-3326046/Lockheed-s-airship-gets-green-light-approves-massive-hybrid-vehicle-launch-2018.html

 

I love it! It has been three full generations since we profitably used lighter-than-air ships. It's about time.

[cdowis]

One obvious application would be to bring disaster relief supplies to remote areas.  That has always been a problem. All you need is a large field and plenty of manpower to offload the supplies.

 

 I wonder about the maximum range and flight ceiling.  

Edited November 21, 2015 by cdowis

[Vort]

 

What I was referring to is that as an object is accelerated, it gains mass.

 

It is not really correct to say that the particle "gains mass"; its rest mass, m₀, remains m₀. Since the (constant) velocity is purely a relative measure according to reference frame, there can be no difference in mass. Rather, the relativistic mass increases according to the perceived or measured velocity. That is strictly a matter of which reference frame you choose.

 

I'm still not certain about the gluons.  But that is the best I can remember.  I'm just getting a little too old, and been away from it too long.  But now I'm trying to teach my kids stuff and they have the most detailed questions.  Yes, my 14 y.o. is asking questions that require relativity to answer.

 

Wasn't that many years ago that I was trying to figure out how to explain time dilation to a ten-year-old. I ended up using the old photon-bouncing-between-two-mirrors-on-a-train setup. It sort of blew his mind, because, hey, relativity is mind-blowing. But he was a bright kid and understood it on a conceptual level. I decided against talking to him about the Lorentz transformations. I expect he will be learning about that by the end of next year, anyway.

 

I was hoping someone had a quick answer that I could say -- Oh! Yah!  That was it.

 

Actually, someone did...

 

So, off to consult the oracles of Google.

 

Good luck. Hope you find an answer you like better. :)

[Guest]

Vort,

 

You are correct about the relative velocities.  But that is only with reference to constant velocities.  A meteoroid traveling through space may be considered stationary when the the rest of the universe is moving.

 

A vessel subject to acceleration is a different story.  Acceleration requires a force.  In no frame of reference is the force applied to the entire universe.  It is only applied to the vessel and whatever method of propulsion it has.

 

Force requires energy.  And energy cannot be destroyed.  It is merely changed from one form to another.  In the case of energy used to accelerate an object, the energy goes into the object in the form of Kinetic Energy measured by the formula KE =1/2mV^2.  But all energy has mass, just a very small amount of it, measured by the formula E=mC^2.

 

What I remember is that any mass must have a physical, material state.  What is it?  Where is the energy stored?  Whether it is kinetic energy of a body or a chemical bond (enthalpy) it is stored.  Where?  What state?

 

I'm supposed to go visit a relative who works for NASA.  I don't believe he'll have the answer, but he should know someone who does.

Edited November 21, 2015 by Guest