Why an Airplane Flies (Bernoulli's Principle vs. Newton's Third Law)

[studiot]

 

In the mean time, perhaps you might like to tell me where the energy comes from to drive the generator.

 

 

Good evening, John.

 

Once again Talos is avoiding the question, as predicted - ain't scientific theory predictions wonderful?

 

That's a very posh explanation of weight.

 

How about simply pointing out that Archimedes (whom Talos has already invoked several times) was the first to distinguish between real and apparent weight?

Edited December 1, 2014 by studiot

[John Cuthber]

Hi

If I wasn't careful, citing Archimedes would look like the logical fallacy of appeal to authority. It's not only a fallacy, but Archimedes got a lot of stuff wrong.

By citing the LPL's website I can point out that they are providing advice on how things are actually done. The stuff about correcting for air buoyancy is my "bread and butter" as an analytical chemist.

I know that if you don't make those corrections you get the wrong answer.so it's based on not just a legally recognised authority (with which Talos might amusingly disagree) but it's based on my own observations.

If he says I'm wrong, he has to explain why it works or call me a liar.

He can't do the first and he will get banned if he does the second.

 

My guess is that he will (once again) ignore the question.

Edited December 1, 2014 by John Cuthber

[Talos]

John and co. Here's an answer from Andrew Hanson, CPhys of the National Physical Laboratory that you quoted.
Outreach Manager
National Physical Laboratory
Hampton Rd | Teddington | Middlesex | UK | TW11 0LW

 

My question was:

I can measure the weight of a deflated balloon.
I can also weigh a bottle of compressed helium.
If I now inflate the balloon from the compressed helium and then weigh the bottle again does the difference in weight equal the weight of helium in the inflated balloon?
YES. THOUGH WEIGHING THEM WILL BE TRICKY AS FOR THE BOTTLE, THE WEIGHT CHANGE WILL BE VERY SMALL COMPARED WITH THE WEIGHT OF THE BOTTLE AND FOR THE BALOON, THE AIR ABOUT IT IS DENSER, SO BOUYANCY WILL HAVE TO BE TAKEN INTO ACOUNT. AT NPL WE WOULD WEIGH THIS IN A VACUUM.

Is it true that the inflated helium balloon therefore has weight?
YES, BUT SO DOES THE AIR ABOUT IT WHICH BEING DENSER WILL RESULT IN BOUYANCY SO THE BALOON WILL FLOAT UPWARDS.

If so, will the balloon gain potential energy when it rises up into the earth’s atmosphere?
IT DEPENDS ON WHAT YOU COUNT AS YOUR SYSTEM. I THINK YOU HAVE TO INCLUDE THE EARTH'S ATMOSPHERE. AS THE BALOON RISES, THE DISPLACED AIR COMING DOWN LOSES POTENTIAL ENERGY AND THE BALOON GAINS IT.

 

 

Nothing in this answer contradicts anything I've said.

 

 

[imatfaal]

A balloon in a vacuum chamber? Surely it would burst.

 

And the comments clearly contradict your assertion that weight has nothing to do with where it is measured.

[studiot]

 

Nothing in this answer contradicts anything I've said.

 

Actually it does.

 

Here is one of the factually incorrect statements you made

 

Talos post#39

Studiot, you say, “Fuel is expended and work done to fill the balloon …”

I say, “the work done in inflating the balloon displaces a volume of air equal to the volume of the balloon according to Archimedes, (ignoring the contribution of Aesop 300 years before him). This means the air in the atmosphere will rise by an equal volume. As the atmosphere rises it increases it potential energy.

However, the balloon already has less mass than the air. Hence

 

Potential energy……….m(air)gh > m(helium)gh

 

It is factually incorrect because at ground zero h = 0 so the inequality you state is factually incorrect.

 

Since h = 0 and PE = mgh, the potential energy for air must equal the potential energy for helium since they both must equal zero.

 

I have done you the courtesy of accepting the potential energy scale and zero point that you have consistently used throughout, and agreeing with you that on this scale PE increases with height above ground level.

This was explained in my post #139 and more fully in the reference I gave there.

 

A further question for you,

 

If I lifted the carbon dioxide filled balloon by means of a crane,

Air would flow in to fill the void.

At least some of this air would come from above, just as with the helium filled balloon.

You say (and I agree) that this descending air would thereby loose some of its gravitation energy.

So where would this PE go to, since it is no longer required to 'lift the balloon'?

[Talos]

Studiot.

Potential energy……….m(air)gh > m(helium)gh

 

You say “It is factually incorrect because at ground zero h = 0 so the inequality you state is factually incorrect.”

I say: Then why does the balloon rise?

 

[studiot]

 

I say: Then why does the balloon rise?

 

Discussion at last. +1

 

Newton's First law :

 

A body continues in its state of rest or motion unless acted on by an external force.

 

The balloon rises, ergo it is acted on by an external force.

 

Notes

1) There is no mention of potential energy, or any requirement that any potential energy possessed by this body be used, or that the body must possess any particular potential energy.

2) A body can still suffer change of motion with no change of PE and Newton's First Law still applies.

3) Equally a body can suffer change of PE, with no change of motion.

4) There is eventual change of PE in this case, but at the outset of motion, no PE is exchanged. That is PE only changes as a result of work being done by the external force.

 

Perhaps together we can answer John Cuthbers' question about the generator. You just need to get the full and complete sequence of events in order for the flight of your balloon.

Edited December 2, 2014 by studiot

[John Cuthber]

As he said,

"HE BOTTLE AND FOR THE BALOON, THE AIR ABOUT IT IS DENSER, SO BOUYANCY WILL HAVE TO BE TAKEN INTO ACOUNT."

So, your own evidence shows that the density of the air affects the weight.

(and that's why they might seek to measure it in a vacuum)

 

Did you not realise you were arguing against yourself?

 

 

On the bright side

"IT DEPENDS ON WHAT YOU COUNT AS YOUR SYSTEM. I THINK YOU HAVE TO INCLUDE THE EARTH'S ATMOSPHERE"

progress at last.

[Talos]

Studiot.

You are forgetting, or deliberately ignoring the fact that there are 3 terms on each side of the inequality—which leads me to ask “what part or parts of the inequality: m(air)gh > m(helium)gh is factually incorrect?”

_____________

Studiot, you say:

A body continues in its state of rest or motion unless acted on by an external force. I agree.

 

There is no mention of potential energy, or any requirement that any potential energy possessed by this body be used, or that the body must possess any particular potential energy. I agree again, but I do ask, what do you think the force is comprised of.

 

A body can still suffer change of motion with no change of PE and Newton's First Law still applies. I agree again.

 

Equally a body can suffer change of PE, with no change of motion. I disagree. If a bodies potential energy changes it must either go up or down.

 

There is eventual change of PE in this case, but at the outset of motion, no PE is exchanged. I think you mean—before the onset of motion, in which case I agree again.

 

That is PE only changes as a result of work being done by the external force. I agree yet again—but I ask again, what is the external force comprised of?

 

John, you say.

So, your own evidence shows that the density of the air affects the weight.

(and that's why they might seek to measure it in a vacuum)

Did you not realise you were arguing against yourself? I am not arguing against myself. I have said that the weight of air is due to gravity and this affects the density—not the other way round.

 

As regards the generator question that you raised, let me say that this is right up my street. Let me also say, that you have been proven wrong in asserting a helium balloon loses potential energy when it goes up in the air. When you can see your error for yourself and explain it to me, then and only then, will I deal with the generator issue.

 

[studiot]

Studiot.

You are forgetting, or deliberately ignoring the fact that there are 3 terms on each side of the inequality—which leads me to ask “what part or parts of the inequality: m(air)gh > m(helium)gh is factually incorrect?”

 

Thank you for that insulting remark (underlined). I am quite capable of performing two simple multiplications and reaching the correct conclusion that when each of the multiplications contains a multiplication by a zero term, then both products are zero and therefore equal and therefore one product cannot be greater than the other.

I also explained this in the original.

 

 

_____________

Studiot, you say:

A body continues in its state of rest or motion unless acted on by an external force. I agree.

 

There is no mention of potential energy, or any requirement that any potential energy possessed by this body be used, or that the body must possess any particular potential energy. I agree again, but I do ask, what do you think the force is comprised of.

 

Discussing that force is definitely my offer, but in the same vein as your comments to John Cuthber, I do not propose to extend to that discussion until we have disposed of previous misunderstandings.

 

 

A body can still suffer change of motion with no change of PE and Newton's First Law still applies. I agree again.

 

 

Equally a body can suffer change of PE, with no change of motion. I disagree. If a bodies potential energy changes it must either go up or down.

 

There are several mechanisms by which this may occur.

A horizontally travelling body will encounter variations of g as it travels. This will not alter its trajectory and therefore h, but will result in a change to the product mgh. This may not be a large effect, but it is not non existant and still obeys Newtons laws.

I noted in a previous post that gravitational PE is not the only sort of PE. A balloon in particular will have elastic strain enery, which is another place the initial inflation work is stored. A side vent which causes horizontal motion will release some of that elastic PE to kinetic energy.

Of course I can simply give the body a charge and let it aquire electric or magnetic PE and then switch off the field. That again would change its PE, without altering h.

 

 

There is eventual change of PE in this case, but at the outset of motion, no PE is exchanged. I think you mean—before the onset of motion, in which case I agree again.

 

I said outset, because I meant outset. This is before motion occurs. But hey, what's the difference of a couple of letters between friends?

Although the point appears trivial, it is in fact important because the force must exist before any energy is transferred. In fact that force can exist indefinitely in a tethered balloon, with no energy exchange taking place at all.

 

 

 

That is PE only changes as a result of work being done by the external force.

 

I agree yet again—but I ask again, what is the external force comprised of?

 

The external force is the resultant of all forces acting on the body, considered as a free body that is not in equilibrium.

Please indicate whether you understand free body diagrams in mechanics so we can discuss this further. I will explain them if necessary.

Edited December 3, 2014 by studiot

[John Cuthber]

 

 

As regards the generator question that you raised, let me say that this is right up my street. Let me also say, that you have been proven wrong in asserting a helium balloon loses potential energy when it goes up in the air. When you can see your error for yourself and explain it to me, then and only then, will I deal with the generator issue.

 

Nope, that's not the way it works.

[MigL]

Oh this is getting ridiculous.

 

We know the mass of the balloon and can determine the mass of Helium filling it.

Considering only the vertical axis, when the only force acting on this mass is gravity, we know that potential is exchanged for kinetic , i.e.motion downward. This is what happens on the airless moon, for example, and can be easily calculated.

If there is more than one force acting on it, but of a negative nature such as bouyancy due to the atmosphere,the potential may be combined,but it is still exchanged for kinetic motion as long as the balloon is not constrained.

If the motion of the balloon is now vertically upward, then we know that the negative bouyant force has a greater magnitude than the gravitational force such that the net force is negative and upwards.

One easy way to check this is to use the same amount of Helium,but filled into a heavier, metal balloon,such that the force of gravity acting on the greater mass. is able to overcome the bouyant force , which hasn't changed.

 

Incidentally this is the first time I've seen one side of an argument state...

'I disagree with you, and when you come around to my point of view, and can explain it to me, then I'll give my argument'

 

I hope I don't see it again.

[Talos]

All of you.

Are you disagreeing with this independant explanation? "AS THE BALOON RISES, THE DISPLACED AIR COMING DOWN LOSES POTENTIAL ENERGY AND THE BALOON GAINS IT."

[MigL]

YES !

[John Cuthber]

Yes, not least because some of the energy may end up driving a geneator that (in contravention of the rules) you refuse to discuss.

[Talos]

On 04 Dec 2014, at 11:21, Talos Perdix <talosperdix@tiscali.co.uk> wrote:

 

Dear Professor Richard Ellis,

Does a helium balloon gain potential energy when it goes up?

 

Yes, any object that rises in a gravitational field gains potential energy.

Jonathan Richard Ellis (CBE FRS)

 

Jonathan Richard Ellis is a British theoretical physicist who is currently Clerk Maxwell Professor of Theoretical Physics at King's College London.)

 

Strange

You say: “Ah, thank you. I guessed it was some sort of failed argument from authority but Google failed me.”

I say: “How much authority do you want?”

 

[studiot]

Talos,

 

What relevence do your posts#163 and #166 have to our discussion?

 

Or have you decided to discontinue it, without having the good grace to tell me?

[John Cuthber]

On 04 Dec 2014, at 11:21, Talos Perdix <talosperdix@tiscali.co.uk> wrote:

 

Dear Professor Richard Ellis,

Does a helium balloon gain potential energy when it goes up?

 

Yes, any object that rises in a gravitational field gains potential energy.

Jonathan Richard Ellis (CBE FRS)

 

Jonathan Richard Ellis is a British theoretical physicist who is currently Clerk Maxwell Professor of Theoretical Physics at King's College London.)

 

Strange

You say: “Ah, thank you. I guessed it was some sort of failed argument from authority but Google failed me.”

I say: “How much authority do you want?”

 

You really don't understand do you?

It's not a matter of who the authority is.

saying "It's true because so and so says it is true" is still a logical fallacy.

Do you accept that?

If so, perhaps you can stop bothering these people.

[studiot]

You really don't understand do you?

It's not a matter of who the authority is.

saying "It's true because so and so says it is true" is still a logical fallacy.

Do you accept that?

If so, perhaps you can stop bothering these people.

 

Note the question Talos asked of these authorities is not the basis of his thesis in this thread.

So their answer to an innocuous question is not suprising, but really a side show to the main issue.

[John Cuthber]

True, but even if he had asked where the energy to run the generator from, (or even "how does a plane fly?" it would still have been a logical fallacy.

 

In much the same way, if he had asked the guy at NPL "Does weight change with air density?" then he would have got the right answer to the right question, rather than a correct answer to an irrelevant one.

 

I get the feeling he's not really trying to learn.

Since he's steadfastly refusing to enter into discussion and citing authorities as if they are some sort of oracle, perhaps we should ask for the thread to be moved to "religion".

Edited December 4, 2014 by John Cuthber

[Talos]

John, I was addressing Strange’s accusation that my argument was some sort of failed argument from authority. I don’t need any authority because I know what I’m talking about. This was for Strange’s benefit.

 

You say, “You really don't understand do you?” Oh yes I do. It is you and your cronies that doesn’t understand. And anyhow, “why should I believe you when higher intellects agree with me.

 

[Strange]

I don’t need any authority because I know what I’m talking about.

 

I haven't seen any evidence of that. You have made a series of counterfactual statements and provided no answers to reasonable questions.

 

 

why should I believe you when higher intellects agree with me.

 

I have seen no evidence of that either.

Edited December 4, 2014 by Strange

[John Cuthber]

John, I was addressing Strange’s accusation that my argument was some sort of failed argument from authority. I don’t need any authority because I know what I’m talking about. This was for Strange’s benefit.

 

You say, “You really don't understand do you?” Oh yes I do. It is you and your cronies that doesn’t understand. And anyhow, “why should I believe you when higher intellects agree with me.

 

Ooh! I haven't been called a "crony" in ages.

 

It seems you still don't understand so I will try to spell it out for you.

It does not matter who the "authority" is because even the greatest authority can be wrong (if you wan't to argue about that from a theological point, please open another thread in the right section, rather than derailing this one).

newton was probably agreed to be the greatest authority of his day concerning kinetics (among other things).

You could, for a few centuries cite Newton as the authority on how things accelerate when acted on by a force.

And yet, as Einstein showed, he was wrong.

 

That's the problem with an "argument from authority". That's what makes it a logical fallacy.

So, please stop trying to convince us of anything by saying "so and so says ... so it must be true".

You just look silly.

 

You would do yourself a lot more favours if you were to address the problems that have been put to you. And, as a hint, once again

"On the bright side

"IT DEPENDS ON WHAT YOU COUNT AS YOUR SYSTEM. I THINK YOU HAVE TO INCLUDE THE EARTH'S ATMOSPHERE"

progress at last."

you were really on the right track there.

Here's another hint; if I store energy in a compressed spring, is that energy in one of the atoms the spring is made from or is the stored energy a property of the whole set of atoms?,

[MigL]

I thought I had been pretty clear in my explanation, but I guess I and others are just banging our heads against the wall.

 

As the balloon rises it does gain GRAVITATIONAL potential. That potential makes it want to fall. That is what gravity does. The buoyant force also has an associated potential, which makes the balloon want to rise.

Since the balloon IS rising, the buoyant force is overcoming the gravitational force, and the net negative potential is decreasing. Note that positive and negative here, are just arbitrarily assigned to up and down directions

In other words, the balloon is gaining kinetic energy upon release, so its net potential is decreasing.

End of story.

I don't care who you ask.

If you'd rather go discuss this with your Professor friend, be my guest.

Edited December 5, 2014 by MigL

[Talos]

John, you say “perhaps you can stop bothering these people.”

I can assure you that they are not bothered, as you put it, but they are more than happy to respond.

 

Your ideas are 15 years behind the times.

I challenge you and, anyone else, to contact the physics departments of any university in the UK or America and, put your argument to the head of department.

Of course you won’t, because I have challenged you and you will be proved wrong—but others might.

 

These links will get you all the universities in the UK and USA.

http://en.wikipedia.org/wiki/List_of_universities_in_the_United_Kingdom#Universities_alphabetically

 

http://www.utexas.edu/world/univ/state/