For example, a kite. I just don’t understand how the higher pressure at the top pushes the plane forward and how it stays in the air and stuff. If anyone could explain this to me would be great!
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The lift does not push a plane or kite forward, simply up. This is what the engine or wire is for.
Lift in a wing works by the air on the top of the wing being directed downwards at the back of the wing, such that there is a downdraft at the back. This provides the equal and opposite force of lift. The specific geometry of the wing allows for this. And you have to have the air moving across the wing with considerable speed for this effect to be significant, thus kites only work in high wind and planes need to be going very fast.
Put your arm out the window flat while you’re driving fast and angle it. Mess around with the angle. All you need is propulsion for the rest.
What you’re describing is the Bernoulli Principle, which is often taught as “how planes fly”
It isn’t.
Or at least, it isn’t the whole picture.
What’s actually happening is that the air is hitting the wing at an angle, that angle is then used to deflect that air downward. Newton’s third law states that any action has an equal and opposite reaction, so push enough air down hard and fast enough and you can push a decent mass of airplane *up* albeit slower than the air.
Propellers and jets use (at a very basic level) the same idea to produce thrust. Sucking air in and deflecting it backwards pushes you forward.
One of the top hits for “how lift works” on YouTube: https://youtu.be/E3i_XHlVCeU
Great route to get questions answered, after Google search. Or if you prefer to read: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/what-is-lift/
Your question kind of bounces around so I don’t know if you really care about the kite. Wings generate lift by traveling through the air and causing the flow to turn downward. In order to turn that air downward it generates a force in the opposite direction. Part of it is a lower pressure on the top and higher pressure on the bottom, but these two don’t explain all of the observed lift.
Edit: “these two…” I think was supposed to refer to the Bernoulli’s principle and Newton’s law’s explanations. I thought it was in the NASA site linked above, but clearly have misremembered.
This one is trickier than it seems.
The full answer? We are not entirely sure.
Here is what we do know.
When air travels over the front of the wing, some of it is deflected under and some over. Some also clings to the wing, creating a boundary between the wing and the rest of the air.
The air traveling over the wing is forced into a path that generates centripetal force, pulling the air away from the wing. This is often because of the curved surface of the wing, but can also be caused by the angle of attack even on a flat wing.
This reduces the pressure on the upper surface of the wing.
The air deflected under the wing, however, travels in much the same path as it would if there were no wing. As a result, its effects on the wing are less than the effects on the upper surface.
There are also other, less well-understood effects coming from other parts of the wing, such as vortices at the tips of the wing. We understand these less well.
Here is the really tricky part, though. Scientists agree that the air going over the upper surface creates a reduced pressure on the wing causing lift. However, they are not certain what translates this reduced pressure into lift. One theory says that this is caused somehow by the interaction between the lower pressure, the boundary, and the wing itself. Another theory is that a downdraft is created pushing the wing up.
In the end, while we would really like to know exactly what is going wrong, what actually allows us to fly is that a lot of engineers kept trying different things until we found one that worked and then worked out the math so that we could generally know what will happen to the wing.
The why, however…
Next time you’re in the car stick your arm straight out of the window and try to keep it straight, pretty self explanatory. Now when there’s more surface area involved, like on a kite, pretty easy to see that force in action
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