Talos

Statement issued with no proof. It’s not a statement, it’s a fact.

Studiot, So, Talos, your University link says that you were wrong and everybody else was right. Re read it. It confirms everything I say. If the air above compresses, the pressure goes up. The air below is at the same pressure, so you have created a situation where there is a pressure difference at the height of the top of the balloon. That's not a stable condition. How does the system maintain the pressure differential? The air pressure below is not at the same pressure, it is increased because the head of air has risen; Archimedes again.

All of you, here’s your answer; taken from question and answers at Department of Physics. University of Illinois at Urbana-Champaign. Question: Consider the three statements 1)Air pressure acts from all directions 2)Air pressure is due to the motion of air molecules 3)Air pressure is caused by the weight of air above Statements 1 and 2 seem logical to me. Statement 3 seems illogical to me -obviously pressure in gases is dependent upon temperature and pressure and will decrease as one rises in the atmosphere but not because of a decrease in the weight of air molecules pushing down from above. My question. is there a fault to my reasoning? Many thanks for your help Stephen - Stephen (age 57) Risch, Zug, Switzerland Answer: Many questions about causation raise philosophical issues, since the meaning of causation isn't very clear. Here I think we all have no problem with the first statement, which is just an empirical fact. Your second statement is a pretty non-controversial one as well, since if you take away the air molecules the pressure goes away and if you keep the same density but have them move slower the pressure is reduced. In fact, you might say that the moving air molecules are the proximate cause of the pressure. So the third statement is the one that bugs you. The atmospheric weight isn't quite as proximate a cause of the pressure as is the local atmosphere. If you quickly removed all the atmosphere above say 1 km (see Spaceballs) it would take a little bit of time before the pressure down here dropped. Essentially no effect would be noticed until time of 1km/(speed of sound) or about 3 seconds. Still, if you removed that weight pretty soon the pressure here would indeed drop, so there's a decent sense in which you can say the weight causes the pressure. The basic point is this: The net force on a column of air above us is zero, in equilibrium. The downward force on it is just gravity, its weight. The upward force is just the pressure of the air down here times the cross-sectional area of the bottom of the column. So the weight does determine the pressure, in equilibrium although not quite instantly. Swansont, Only the air above compresses? How does that work, exactly? The inflated balloon has the same pressure inside as the air outside.

All over the world there are compressed air containers that are full of high pressure air. Someone already took lots of air from the atmosphere and put it into those containers. Yet balloons still rise John, if all the compressed air in these containers were discharged back into the atmosphere it would rise and increase it potential energy. Also, It’s not the atmosphere’s height that causes balloons to rise, but the potential energy they contain compared to an equal volume of air around them. This is true for a carbon monoxide balloon; so it can’t rise, whether in the atmosphere or a closed environment. I haven’t forgotten your question about the generator and will answer it in due course.

Swansont, If the conjecture is right, then if you inflate a helium balloon in a closed room, it shouldn't rise, since the displaced air can't simply go up. I think we can conclude that this isn't the case. Inflating a balloon in a closed environment will still displace a weight of air equivalent to the volume of the helium. The displacement however comprises air which is compressed. This again means it has greater potential energy, just as if it had risen, as before.

Also, take a look here. http://forums.udacity.com/questions/9007092/energy-conservation-problem-regarding-gas-balloon

Where do you think the atmospheric pressure comes from? I take it that you don’t know.

You state that the balloon causes the atmosphere to rise. Why so? Archimedes and Aesop. Suppose I removed some air adjacent to the balloon (perhaps by freezing it) and equal in volume to the balloon, Would the atmosphere now rise? No. Would the balloon still rise when released? No. It requires the displaced air to descend. The atmosphere hasn’t risen so it doesn’t descend. Archimedes again. What would happen if I filled the balloon with carbon dioxide instead of helium by mistake? Would the balloon skin not still push back the atmosphere by the same amount? Yes. But the carbon dioxide has greater potential energy than the air. So the air will not descend. The point is that the apparatus that inflates the balloon causes the balloon volume to increase against the pressure of the atmosphere around the balloon skin. Work is done against this pressure and is equal to the volume change times the pressure. Since this work is done against the atmospheric pressure energy is transferred to the atmosphere as pressure energy, not gravitational potential. You’re wrong. Where do you think the atmospheric pressure comes from?

Studiot, When we inflate a helium balloon it displaces an equal volume of air. Do you not agree? This causes the atmosphere to rise by an equal volume. Do you not agree? When the atmosphere rises it increases its potential energy. Do you not agree? When we release the balloon the air around it descends. Do you not agree? The descending air then begins to lose some of the atmosphere’s increase of potential energy that inflating the balloon caused. Do you not agree? The descending air’s loss of potential energy has to go somewhere. Do you not agree? It can only go into the balloon. Do you not agree? If the helium escapes or the balloon bursts at any height it will descend to the ground changing its potential energy to kinetic energy as it falls. Do you not agree? The balloon therefore gained potential energy when it rose. Do you not agree?

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 Gravity pulls more on the heavier air than the helium, hence air descends and the balloon rises. Eventually, because the air gets lighter with height the balloon will occupy the same as an equal volume of air that has the same potential energy. Gravity then pulls equally on the air and the balloon, and the balloon stops rising. Potentail energy……….m(air)gh = m(helium)gh You continue, “or drive the aeroplane”. I say, “Newton’s first law states ‘every body continues in its state of rest or uniform motion in a straight line except in so far as it is compelled by external forces to change that state.” This law says the airplane will continue in a straight line unless an external force acts on it. The only new force acting on the airplane is drag. Once up to level flying speed the engine no longer provides the airplane with lift, it only counteracts the drag. A glider incurs drag which in stationary air causes it to lose height. I.e., it loses potential energy. This lost energy manifests itself as kinetic energy in the air that is dragged along with the airplane, vortices and all. The energy needed from an engine in countering the drag is therefore the same as the kinetic energy in the air, is the same as the potential energy lost by the air. A satellite in space travelling at orbital velocity does not require any engines to keep it up, because there is no drag in space. In your last post, you say, “Talos, do you just wish to preach or are you interested in discussion, which involves acknowledging the contributions of others present in the discussion?” I say, “No, I don’t want to preach, but I do want to correct errors, misconceptions and wrong ideas. If this is preaching, then so be it. John Cuthber, you say, “When a helium balloon rises up it gains potential energy. No it doesn't.” I say, yes it does. You continue, “If I have a big He balloon at ground level, I can tie a string to it and wrap that sting round the shaft of a generator. If I let go of the balloon I can get electricity from the generator. I agree. You continue, “If I start with the balloon further up I can't get as much electricity before the lift from the balloon is too small to turn the shaft. So, as the balloon rises it looses potential energy. I say, “If you start with the balloon further up it has already acquired potential energy but it still has some more to acquire. You’re forgetting about the energy already extracted from the air.” Your argument is like saying “if I start with a half full tank I can’t get as much energy from the tank. You continue, “How does the displacement theory explain where the energy comes from?” You tell me- it's not my theory. I say, “At the risk of rolling Archimedes over in his grave, the displacement theory is a simple illustration of a more complex issue. The issue is concerned with energy. Everything contains energy, whether it be potential energy, kinetic energy or strain energy, or some other form of energy. In essence, a change of one type of energy results in a different form of energy. Hence, air that descends, like everything that descends, loses potential energy and this must go somewhere. It can only go into the balloon; so the balloon gains potential energy as it rises.

Thanks for the reminder. Our other website is: www.talosperdix.com You may find some more apparently contradictory views. You could also take a look and listen to this David F. Anderson TED talk on understanding flight: It lasts about 50 minutes. http://www.youtube.com/watch?v=hQ99JkaOwEk

My initial post has certainly opened up a bag of worms. Perhaps I should have simply said...take a look at this website. http://www.vortex-dynamics.com.au/The%20Coanda%20Effect%20and%20Lift.pdf Talos

Cuthber, When a helium balloon rises up it gains potential energy. The higher it goes the more potential energy it acquires. Where does this energy come from? How does the displacement theory explain where the energy comes from? What is it that loses potential energy in order for the balloon to gain it. Likewise, an airplane gains potential energy when it goes up. What is it that loses potential energy in order for the airplane to gain it?

Studiot, take a look at my website, talosperdix, downwash page. You'll see the downwash descend behind an airplane 's wings. It is truly frightening.

Airplanes can and do fly in stationary air. This means air cannot flow across the wings. The airplane moves...not the air. So bernoulli has nothing to do with lift. A wind tunnel uses moving air across a stationary wing, and those with tunnel vision assume that Bernoulli is proven. This is on a par with Ptolemy who said the heavens go round the Earth. We all know that Ptolemy was wrong... and pretty soon we'll all know that the use of Bernoulli's theorem is wrong in explaining lift. Incidentally, the physics that explain the lift of an airplane are the same as the physics that explain the lift of a helium balloon. Put simply: air must descend in a downwash in order to produce lift.