Things I want to know

[doodab]

I want to know why I always weigh more after my morning poo.

[Spacecadet]

Yes, there air pressure is lower above the wing than below, but it's easier to think in terms of Newton. It's just lots of collisions with air molecules. As the glider moves along it pushes air molecules down and the change in momentum of those molecules results in an equal and opposite force that pushes the glider up.

You can see this perhaps more clearly with a helicopter, which is basically lots of wings going around in a circle. I think you can see here that the force (equal to the helicopters weight) would be felt on the floor.

Helicopter blades are angled to physically push the air down, which is why I specified my assumption in the gliding principle involved as most aircraft attack the air in such away as to deflect some of it downward during flight.

[Spacecadet]

I want to know why I always weigh more after my morning poo.

That'll be the hamburger you're scoffing at the same time

[doodab]

That'll be the hamburger you're scoffing at the same time

Oooh no you can't eat on the loo.

It could be the coffee though.

[TimberWolf]

Helicopter blades are angled to physically push the air down, which is why I specified my assumption in the gliding principle involved as most aircraft attack the air in such away as to deflect some of it downward during flight.

Okay lets say the glider is pulled up by a pressure difference. A lower air pressure above the wing. Less molecules batting the top of the wing than below, or rather less momentum per unit time. Where did that pressure difference come from? Air that would have hit the top of the wing was batted away (downwards) before it reached the top wing. There's always batting down going on and without the batting down there would be no partial vacuum above the wing either.

[SimonMac]

1. If you hold in a trump, where does it go? Does it get absorbed inside (yuk)?

They end up as posts like this, why do you think Wilmslow never farts

[Spacecadet]

Air that would have hit the top of the wing was batted away (downwards) before it reached the top wing.

wrong

The difference in pressure is due to the difference in relative speeds

[mudskipper]

1. If you hold in a trump, where does it go? Does it get absorbed inside (yuk)?

"Where do farts go when you hold them in?

How often have you held in a fart, intending to release it at the first appropriate opportunity, only to find that the fart has disappeared when you are ready for it?
I asked several doctors where the fart goes. Does it leak out slowly without the person knowing it? Is it absorbed into the bloodstream? What happens to it?
The doctors agree that the fart is neither released nor absorbed. It simply migrates back upward into the intestine and comes out later.
It is reassuring to know that such farts aren't really lost, just delayed."

Lots more useful fart facts too.


Facts on Farts

[TimberWolf]

wrong

The difference in pressure is due to the difference in relative speeds

It's not wrong, there's more than one way of explaining it.

Let's try this. The glider, which for sake of convenience is maintaining altitude, must have a force mg acting in the upward direction on it for it to maintain a steady height. There's no escaping that. Some force mg is pushing it up from below, or if you like some force is pulling it up from above.

In the first case we have a force (of air) pushing up and that force has an equal and opposite force at the floor, which is equal to the weight of the glider.

In your second case, you'd like to say, it's a vacuum pulling the glider up and to balance that force, the roof of the truck is being pulled down with a force of mg. The weight hangs off the roof, it's not on the floor.

It's one or the other. You can't magic away the weight of the glider.

Well in both cases the truck is heavier with the glider inside!

[Spacecadet]

It's not wrong, there's more than one way of explaining it.

Let's try this. The glider, which for sake of convenience is maintaining altitude, must have a force mg acting in the upward direction on it for it to maintain a steady height. There's no escaping that. Some force mg is pushing it up from below, or if you like some force is pulling it up from above.

In the first case we have a force (of air) pushing up and that force has an equal and opposite force at the floor, which is equal to the weight of the glider.

In your second case, you'd like to say, it's a vacuum pulling the glider up and to balance that force, the roof of the truck is being pulled down with a force of mg. The weight hangs off the roof, it's not on the floor.

It's one or the other. You can't magic away the weight of the glider.

Well in both cases the truck is heavier with the glider inside!

The air would be pushing down on the floor of the truck whether the glider was there or not

The air above the wings is moved but it is only a localised effect, so unless the glider is very close to the roof the effect would be zero

The weight of the glider is not being "magically" taken away, it is being partially supported by the reduction in forward momentum. The rest is simply not supported and results in a decrease in the gliders altitude (you can't magically have a glider which maintains altitude without external forces above the lift provided by the wings)