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

[Strange]

You'll never know. I've decided that none of you want to learn.

 

You are so unwilling to answer questions or explain your ideas that I can only assume you don't understand them yourself.

PPL? Pokémon Puzzle League

[John Cuthber]

Sorry John,

You'll never know. I've decided that none of you want to learn.

I've never come across such a conceited bunch of amateurs.

Talos. British Airways Electrical and Electronics Engineer and PPL(UK) holder.

For a start, there's no way that could possibly be your decision is there?

You don't get to decide what we want; so you are just being silly when you say " I've decided that none of you want to learn"

 

 

The idea that I don't want to learn does not make sense and you know it.

If I did not want to learn,, I would not keep asking questions.

So, here we go again.

How do you explain this?

"Also, you have not explained how a balloon on a string can generate electricity by rising unless that energy is taken from the potential energy of the balloon.

If energy is taken from it as it rises then it must have less potential energy when it's high up."

on the other hand, if you wanted to learn you would try to answer the question. it is you who refuses to even try to learn, not us.

 

 

Having a private pilot's license has little to do with knowing how a plane flies.*

Plenty of people drive cars without having the least understanding of the mechanics of the engine.

Why did you mention it?

Did you think it would impress us?

Boy oh boy! you have e lot to learn.

 

 

* The proof of that assertion is that you have one, but don't know how a plane flies.

Edited November 25, 2014 by John Cuthber

[Strange]

 

Having a private pilot's license ...

 

Ah, thank you. I guessed it was some sort of failed argument from authority but Google failed me.

[John Cuthber]

Well, I'm guessing that's what he meant.

It hardly matters- an unclear logical fallacy isn't an improvement on a clear one.

If I wanted an expensive taxi driver the ppl would be relevant (Though I'd probably ask a mate of mine who teaches people to fly helicopters).

[Talos]

John, you say "I have not explained how a balloon on a string can generate electricity by rising unless that energy is taken from the potential energy of the balloon.”

You are putting words into my mouth. I am not saying the energy comes from the balloon. It is you who is saying this.

 

You go on to say “If energy is taken from it as it rises then it must have less potential energy when it's high up."

Really! What are you thinking?

 

[studiot]

John, you say "I have not explained how a balloon on a string can generate electricity by rising unless that energy is taken from the potential energy of the balloon.”

You are putting words into my mouth. I am not saying the energy comes from the balloon. It is you who is saying this.

 

You go on to say “If energy is taken from it as it rises then it must have less potential energy when it's high up."

Really! What are you thinking?

 

 

This is this most reasonable post you have made.

 

Since you have an alternative explanation, the way is clear for you to state it.

 

I do agree, however, that any electrical energy generated does not arise from the gravitational potential energy of the balloon.

[John Cuthber]

John, you say "I have not explained how a balloon on a string can generate electricity by rising unless that energy is taken from the potential energy of the balloon.”

You are putting words into my mouth. I am not saying the energy comes from the balloon. It is you who is saying this.

 

You go on to say “If energy is taken from it as it rises then it must have less potential energy when it's high up."

Really! What are you thinking?

 

What I'm thinking is the same as what I'm saying..

If the balloon can give energy to something else as it rises then it must lose energy as it rises.

So it must have less energy when it it high up.

 

Would you like to explain where else the energy might come from?

[studiot]

 

If the balloon can give energy to something else as it rises then it must lose energy as it rises.

So it must have less energy when it it high up.

 

If there's a leak in my bath plug does it follow that I can't fill my bath?

[MigL]

Well way to go, John, Studiot and Strange.

We may have lost another productive and valuable member because of your strict adherence to logic, facts and common sense.

 

When will you guys learn !

[studiot]

Canadians +1

[Talos]

John, your post dated 10 November includes this statement: “the helium in the balloon loses potential energy as it rises.”

I say you are wrong. Helium has mass, or have you forgotten?

The potential energy of helium = m_heliumgh—and this means it will gain potential energy along with the rest of the balloon, as height h increases.

 

[studiot]

What I'm thinking is the same as what I'm saying..

If the balloon can give energy to something else as it rises then it must lose energy as it rises.

So it must have less energy when it it high up.

 

Would you like to explain where else the energy might come from?

 

John, you say "I have not explained how a balloon on a string can generate electricity by rising unless that energy is taken from the potential energy of the balloon.”

You are putting words into my mouth. I am not saying the energy comes from the balloon. It is you who is saying this.

 

You go on to say “If energy is taken from it as it rises then it must have less potential energy when it's high up."

Really! What are you thinking?

 

 

 

John, your post dated 10 November includes this statement: “the helium in the balloon loses potential energy as it rises.”

I say you are wrong. Helium has mass, or have you forgotten?

The potential energy of helium = m_heliumgh—and this means it will gain potential energy along with the rest of the balloon, as height h increases.

 

 

And John has consistently maintained this throughout the thread.

 

The difference is he has offered a reason for his view.

You simply reiterate yours without support as yet again in the quote above.

 

Moreover you have never once offered a view as to where the energy of the generator comes from, if not from the gravitational potential energy of the balloon, although you promised to do so and have been repeatedly asked for this.

 

Way back, I even agreed with you, but I have been waiting for you to show that you understand the mechanics of your statement and are not just blindly quoting others.

 

I am still waiting.

[John Cuthber]

John, your post dated 10 November includes this statement: “the helium in the balloon loses potential energy as it rises.”

I say you are wrong. Helium has mass, or have you forgotten?

The potential energy of helium = m_heliumgh—and this means it will gain potential energy along with the rest of the balloon, as height h increases.

 

OK, Lets try that again, but do it properly.

If you want to calculate the gravitataional potenetial energy of something it's easy enouh

E= m g H

where m is the mass, g is the local gravitational acceleration and h is the height above some datum.

 

There's a similar calculation for weight

w = m g

So you can rewrite the first equation in terms of weight

the gravitational potential energy is given by

E = w h

where w is the weight and h is the height.

But, for a helium balloon, measured in air, the weight is negative.

So the more height you have the more negative the energy is.

 

The problem is not that I had forgotten that helium had mass,but that you had forgotten that its weight is negative (if measured in air at a comparable t and p).

Blindly quoting high school physics doesn't get you very far in this case; you actually need to think about the system and the forces involved.

 

So, as you have been asked repeatedly, and as the rules require,

Perhaps you might like to tell us where the energy to run the generator comes from.

Edited November 30, 2014 by John Cuthber

[studiot]

I also said, a while back, that Talos and John are talking about different things in the GPD (Great Potential Energy Debate)

 

Both views are presented here.

 

http://hyperphysics.phy-astr.gsu.edu/hbase/gpot.html#gpt

 

and again here

 

http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/gravpe.html#c1

 

So, because of a difference of origin both Talos and John are correct and gravitational Potential Energy can be regarded as positive or negative to suit.

 

However both must agree that it takes external work to lift an object, even a helium balloon, from the surface to height, h, whether you count that work positive or negative.

 

The important fact is that (from the equations) that work is the same whether the balloon is contrived to generate electricity or not in the course of its ascent to h Further h is quite independent of the quantity of electricity generated.

Edited November 30, 2014 by studiot

[John Cuthber]

Whether a rock has gravitational potential energy or not depends on where your baseline is, and you can't say for certain whether its energy is positive or negative.

However when a helium balloon rises it does work against the viscosity of the air and heat is produced via friction.

The ability of a balloon to fly i.e. lift a load relies on it having stored energy.

Once it has lifted the load it has less energy.

In context it's perfectly clear that the potential energy of a helium balloon is lower when it's high up.

 

Perhaps the most important point here is that it has nothing whatsoever to do with the topic.

 

Why air planes fly isn't really the same as why ballons fly

[studiot]

 

The ability of a balloon to fly i.e. lift a load relies on it having stored energy

 

Although there is energy stored in the balloon, this is not the energy to fly. This energy is not stored in the balloon.

 

Will a balloon rise in a vacuum?

 

 

Whether a rock has gravitational potential energy or not depends on where your baseline is, and you can't say for certain whether its energy is positive or negative.

 

Agreed, which is why you should specify your baseline.

This applies to any object with mass, including helium balloons, not just rocks.

 

 

However when a helium balloon rises it does work against the viscosity of the air and heat is produced via friction.

 

Yes indeed and the work against air friction has the same source of energy as the work of electricity generation during the ascent.

This source of energy springs from an agent external to the balloon.

 

 

In context it's perfectly clear that the potential energy of a helium balloon is lower when it's high up.

 

 

No it's quite clear by both the equations you quoted and since the source of energy is not the gravitational PE, by whatever measure, the gravitational energy is unaffected by work done.

Edited November 30, 2014 by studiot

[John Cuthber]

 

Although there is energy stored in the balloon, this is not the energy to fly. This energy is not stored in the balloon.

 

Will a balloon rise in a vacuum?

 

 

Agreed, which is why you should specify your baseline.

This applies to any object with mass, including helium balloons, not just rocks.

 

 

Yes indeed and the work against air friction has the same source of energy as the work of electricity generation during the ascent.

This source of energy springs from an agent external to the balloon.

 

 

No it's quite clear by both the equations you quoted and since the source of energy is not the gravitational PE, by whatever measure, the gravitational energy is unaffected by work done.

The balloon won't fly in a vacuum. nor will a plane.

Another thing that won't fly is the idea that flight in a vacuum is the context of this thread.

 

The source of energy is indeed external to the balloon.

But if you had a balloon twice as big you would have twice as much energy available for the generator.

 

Ignoring the fact that the balloons would burst, if you tied two balloons together by a string and hung them over a pulley nothing much would happen.

But if one balloon was full of air and the other of helium, the helium balloon would rise.

So, in that context, a helium balloon would rise in a vacuum.

[studiot]

 

But if you had a balloon twice as big you would have twice as much energy available for the generator.

 

Perhaps, but I would say the length of the string was more significant than the size of the balloon.

[John Cuthber]

Indeed, and it still as nothing to do with the topic.

[studiot]

 

and it still as nothing to do with the topic.

 

 

Odd, but I could have sworn that you introduced the balloon powered generator, although Talos introduced the balloon.

[John Cuthber]

He introduced quite a lot of twaddle, notably this.

"Incidentally, the physics that explain the lift of an airplane are the same as the physics that explain the lift of a helium balloon."

[studiot]

 

He introduced quite a lot of twaddle,

 

Yes we are all agreed on that.

 

He also tried to avoid the question every time someone asked a searching question about his statements.

 

I particularly noted his attempts to avoid answering swansont's question about the closed room.

[John Cuthber]

His behaviour on that count suggests that he doesn't really understand what he's on about; and he knows it.

I guess the book he is parroting doesn't answer those questions for him.

[Talos]

John, you say “for a helium balloon, measured in air, the weight is negative. So the more height you have the more negative the energy is.”

I say, weight has nothing to do with where it is measured. Gravity gives a mass its weight, and it can never be negative.

If I have a 1 kg weight and a 2 kg weight on either side of a balance scale the 2 kg weight will descend and the 1 kg weight will rise. I could argue, like you, that the 1 kg weight is negative, but that doesn’t alter the fact that it gains potential energy when it rises.

 

[John Cuthber]

 

I say, weight has nothing to do with where it is measured.

You may very well say that.

However you are plainly wrong for a number of reasons.

This page discusses the particular error that is relevant here

http://www.npl.co.uk/upload/pdf/buoycornote.pdf

 

Other reasons you are wrong include the spin of the Earth, latitude, altitude and more fundamentally, whether you are on Earth or not- you weigh roughly 6 times less on the Moon.

Did you not realise that if I had made such a fundamental error others would have pointed it out?

 

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

Edited December 1, 2014 by John Cuthber