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

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arc

The pressure that is raising the balloons from below is being opposed by the resistance that the rougher surface has on the downward flow of the displaced air as it moves past the rougher surface, thus slowing the balloon's rise. But its lift capacity remains the same due to the pressure and the gravity that provides it. This shows that you are incorrect and the force that provides the lift is not the air that is moving down from above.

Yes, you have reached into the crux of the energy question.

The work done on the balloon by the lift forces not only provides potential energy to the balloon, it also provides kinetic energy.

Some of this kinetic energy is lost overcoming friction and slows the balloon.

Some may also be used powering John Cutherber's generator.

arc

Lift of the balloon will not be provided without displacement by a lower density of equal or greater volume, but displacement is not the force that provides lift. Hydrostatic pressure of the surrounding volume through gravity is.

This needs tidying up, however, in the light of my post#196 since the lift force derives from the internal gas in the case of non rigid balloons.

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Yep. Talos has clearly confused cause and effect.

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StringJunky,

By your logic then: a brick and a feather free-falling in a vacuum would fall at different rates because the Earth is pulling more on the brick than the feather, which is not correct. The gases with a higher molecular weight than helium push the helium atoms out of the way and assume a lower position.

Your comment is the most sensible so far. However, free falling in a vacuum is not applicable in an atmosphere.

The volumetric weight of a feather is more than an equivalent volumetric weight of air. This means air will not descend and lift the feather up like it would a balloon.

When we inflate a balloon with helium its volumetric weight decreases.

When a point is reached beyond which the balloon’s volumetric weight is less than an equivalent volumetric weight of air, the air will descend and lift the balloon up.

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Well, this tells you what a volumetric weight is.

http://www.online-calculators.co.uk/volumetric/weight.php

And, as I thought it might, it has nothing to do with what Talos is on about.

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When a point is reached beyond which the balloon’s volumetric weight is less than an equivalent volumetric weight of air, the air will descend and lift the balloon up.

"the air will descend and lift the balloon up."

Talos,

Sure, and when a rock sinks the water rising past it pushes the rock down. The air moving around a car is pushing it forward. An elevator works like the balloon.

And now, thanks to you I'm totally confused as to how a sailboat works!

Anyway, I'm still waiting for your response to those two other posts.
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John,

Well, this tells you what a volumetric weight is.

http://www.online-ca...tric/weight.php

And, as I thought it might, it has nothing to do with what Talos is on about.

Obviously you have no idea what a volumetric weight is, as evidence this commercial definition for the purpose of costing.

Arc,

Sure, and when a rock sinks the water rising past it pushes the rock down. The air moving around a car is pushing it forward. An elevator works like the balloon.

You know as well as I do that this is claptrap.

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!

Moderator Note

OK, I think that was the final straw.

Talos - you seem to be more interested in the process of arguing than in understanding the points of view of others and you are prioritising scoring points over explaining your idea. This trolling is not acceptable and I am going to lock this thread pending staff review.

Do not open a similar thread to continue the argument.

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