Watch the launch of a Saturn V rocket. At the base of the launch pad the smoke from the initial ignition is pulled into the flame trench by the engine exhaust at full thrust. If you watch the motion of the smoke, it clearly shows it being pulled from the bottom up. So depending on circumstances air can pull.
I was taught that the sails, on any tack other than a run, pushed the boat down in the water and the boyancy and shape of the hull pushes the boat in the desired direction. Most however, blame it all on the Bernoulli Effect.
The AF taught the pressure method in the 70s. Most recently, they go with Newton and simply say that a mass is accelerated rearward. This was the teaching of the Civil Air Patrol. I think both are correct but the point was standardization.
hi roland
Yes - just spent some time reviewing the entire entry on Wiki. Amazing stuff!
The air flowing over the top of the wing has a longer distance to travel in the same amount of time then the air under the wing does. This results in lower pressure over the top of the wing. Since nature abhors a vacuum and is always trying to even things out, is the higher air pressure below the wing trying to push its way into the lower pressure or is the lower pressure trying to pull the higher pressure in? What say all you aviators out there.
It's useful to understand how the sail's behaviour changes depending on how it is presented to the wind, and we can usefully divide that behaviour into what we call "lift" and what we call "drag." But the distinction between "pushed" and "pulled" is arbitrary semantics.
If you want a headache, here is a good read on the subject. Bernoulli is to blame in any event.
All I know is on a small boat, if a strong gust comes and you can't change the attitude of the mainsail you are going to get wet.
That is exactly how it works. The speed provided by the engines produces a great enough differential between the low pressure above the wing and the higher pressure beneath the wing to lift the plane. The air movement over the wings (in sailing terms, “apparent wind“) neither pushes nor pulls, but rather the pressure differential moves the wing (or sail) from high pressure to low pressure according to Bernoulli’s statement that “nature abhors a vacuum.”
That’s a different situation. The air under the parachute must be displaced, and the resistance to displacement produces a vector opposite in direction to the force of gravity. Sometimes a parachuter moves upward!
That‘s a very practical way to think about it, but it’s actually Bernoulli’s law that is in effect.
