There's a youtube channel Veritasium which is super cool and science-y and you should all watch if you aren't already. Here are two videos he posted that lead to my question.
Ok, so what I learned from video 1 is that if you have a spinning ball moving forward, one edge will be moving forward more slowly due to the spin and its opposite edge will be moving forward more quickly due to the spinning. This faster edge in essence hits the air and stops it, while the other edge allows air to flow more smoothly around it. Then, at the back of the ball, the flowing air gets deflected and Newton's 3rd Law moves the ball towards the slower edge.
From video 2, I learned that if you have a ball moving forward, one edge may be rougher than the opposite edge, either due to the seam, or putting something on that edge, or polishing the opposite edge. Because of the roughness, the air it encounters is more turbulent, and turbulent air sticks closer to the ball. This more turbulent air on the rough side is then deflected more at the backside of the ball than the calmer air from the smooth side, so the ball moves in accordance with Newton's 3rd Law again to the rough side.
The problem I have is that I'm imagining these 2 videos to be describing much the same thing. Why is it that when the ball is spinning, the faster moving side contacts the air and stops the air somewhat so that it doesn't stay with the ball as much, but the seam contacts the air, makes it turbulent, and then that air sticks more to the ball? Don't these sound contradictory to anyone else?
Can this be related to the principle by which a wing creates lift? My understanding is the wing's shape forces the air on top to travel further than the air on the bottom and thus the top air must move faster. The principle then being that faster moving air across a surface has a lower pressure than slower moving air.
Which is confusing to me because it seems like by this principle, curve balls curve the wrong way.
Can this be related to the principle by which a wing creates lift? My understanding is the wing's shape forces the air on top to travel further than the air on the bottom and thus the top air must move faster. The principle then being that faster moving air across a surface has a lower pressure than slower moving air.
Veritasium has a video on wings too, which I recommend. The conclusion is that you're sort of right. Flat wings also fly, so the wing shape can't be all. But wings are angled upward, so they deflect air downwards and in return get lifted upwards. You can find many videos and articles on how planes fly, and by my recollection of doing this in the past, the common explanation that you provided isn't really sufficient.
And still, my issue is why is the faster edge of a spinning ball not the same as the seam if both disrupt the air flow on their side?
The seam induces turbulence which delays separation of the boundary layer from the ball's surface so it causes the ball to curve towards the seam side.
Spin about the vertical axis creates one side of the ball moving against the air flow (faster) and one moving with the air flow (slower). I put the terms in parenthesis because I think there is a fair chance that language is causing some of the problem. The side moving with the air flow (remember the air flow is opposite in direction to the ball movement) speeds the air flow and causes it to move further around the ball than the opposite side which slows the air flow somewhat. That causes the ball to deflect to the slow side.
Just a nit point, all of the effects in his videos have been known for more than a hundred years. He claims to have discovered something, but that is nonsense.
Spin about the vertical axis creates one side of the ball moving against the air flow (faster) and one moving with the air flow (slower). I put the terms in parenthesis because I think there is a fair chance that language is causing some of the problem. The side moving with the air flow (remember the air flow is opposite in direction to the ball movement) speeds the air flow and causes it to move further around the ball than the opposite side which slows the air flow somewhat. That causes the ball to deflect to the slow side.
So "the slow side" at the end refers to the side "moving with the air flow (slower)" from above - i.e. referring to ball speed. So that's the side where the air flow speed is faster. So it is like wing shape producing lift by forcing air on one side to move faster thus reducing air pressure on that side?
If you want to see a ball with no seams really do some curving, throw a beach ball with some spin on it.
So "the slow side" at the end refers to the side "moving with the air flow (slower)" from above - i.e. referring to ball speed. So that's the side where the air flow speed is faster. So it is like wing shape producing lift by forcing air on one side to move faster thus reducing air pressure on that side?
If you want to see a ball with no seams really do some curving, throw a beach ball with some spin on it.
PairTheBoard
Some articles I've read recently indicate that this description of an airfoil is pretty much hogwash even though there are still text books that teach the method.
The reason the articles provided why airfoils cause lift is because they force air to flow towards the ground and thus generate a reaction of a net lifting force upwards (i.e. away from the ground) per Newton's 3rd law.
If I remember some of the questions that lead away from using the Bernouli's Principle Buoyant force were:
1. Why can planes fly upside down if the shape of the airfoil (which presumably causes the buoyancy effect) is now reversed and should be causing a net downward push?
2. Why do relatively flat airfoils still produce lift?
3. Why should 2 air particles that diverge over different parts of the air foil meet up again at back of the airfoil? What force causes the one air particle to accelerate?
I believe once they were able to measure airspeed over the top of the foil there was some evidence indicating air was not moving as quickly as would be have been predicted to generate lift.
This is all from memory though so apologies. I do know one of the articles was this one:
Some articles I've read recently indicate that this description of an airfoil is pretty much hogwash even though there are still text books that teach the method.
The reason the articles provided why airfoils cause lift is because they force air to flow towards the ground and thus generate a reaction of a net lifting force upwards (i.e. away from the ground) per Newton's 3rd law.
Before I'd ever heard of the wing-shape thing common sense told me the air hits the slanted wing and pushes it upward. Then I was told, no, it's the wing shape. So I can accept the slanted wing providing lift. But now my question is, what if you left the wing unslanted? Could a plane fly from lift due just to the wing shape where the underside of the wing is level?
Before I'd ever heard of the wing-shape thing common sense told me the air hits the slanted wing and pushes it upward. Then I was told, no, it's the wing shape. So I can accept the slanted wing providing lift. But now my question is, what if you left the wing unslanted? Could a plane fly from lift due just to the wing shape where the underside of the wing is level?
PairTheBoard
I am not a fluid dynamics, aero dynamics, or aeronautics expert. My interpretation is that as long as the airfoil is designed to produce the conditions that allow air to flow downward (towards the ground) then the 'equal and opposite reaction' of this downward flow of air will be a lift force which causes the plane to fly.
I have no idea if the wing needs to be slanted to produce the correct conditions or not.
I am not a fluid dynamics, aero dynamics, or aeronautics expert. My interpretation is that as long as the airfoil is designed to produce the conditions that allow air to flow downward (towards the ground) then the 'equal and opposite reaction' of this downward flow of air will be a lift force which causes the plane to fly.
I have no idea if the wing needs to be slanted to produce the correct conditions or not.
As I understand the wing shape, if it's level the air flowing underneath should travel level while the air on top should travel up and over the hump in front and then down the upper side of the wing.
As I understand the wing shape, if it's level the air flowing underneath should travel level while the air on top should travel up and over the hump in front and then down the upper side of the wing.
PairTheBoard
The forces on the airfoil are not only influenced by it's shape, but by the angle of it's approach within the fluid and the viscosity of the fluid.
All those topics need to be studied with fluid mechanics equations and simulations and numerical analysis and the rest are very dangerous routes that can appear convincing and be wrong as arguments etc. Its all very complex eventually when the systems get nontrivial in geometry. Just solve it and leave the qualitative analysis away lol.
