In The Shower..

[ferlew]

this morning, pondering life, as you do, and I noted the shower curtain was pulled toward my body. Then I got to wondering why. Surely with the force of the water into an enclosed space, and the steam produced, why doesn't the curtain billow away from me?

[tonyav]

Have a look at this, ferlew.
http://stopyourshowercurtainblowingin.blogspot.co.uk/

[ivor4781]

presumably with the hot air from the hot water rising it's pulling cooler air into the lower half of the shower hence your curtain is moving in

[ivor4781]

ya just beat me tony :-)

[tonyav]

Never mind ivor, she has her answer.

[ferlew]

Well, would you credit it, thank you Tonyav.

[ferlew]

I'll have to find something else to ponder tomorrow now ;)

[tonyav]

Try having a sing song, ferlew ;-)

[New Judge]

It is more the “Bernoulli Effect” than the chimney effect. As the article says, the effect is still evident when cold water is used. The same symptoms can be seen on curtain sided trucks travelling at speed. Their curtains billow inwards due the speed differential (and hence pressure differential) of the air mass inside and that outside the lorry. A mass of air moving faster relevant to another mass has less pressure (and that's how aircraft fly because the air flowing over the top of the wing has further to travel than that underneath. It moves faster and so has less pressure).

[Clanad]

So then, New Judge, how does an airplane fly upside down or straight up (given enough power)?
Fact is the air on the upper side of the wing is 'thrust' downward by the curvature of the upperside and therefore accelerated, giving it an "action " awaiting a reaction as in Newtonian 3rd law...

To be accurate as well as fair... you're not entirely 'wrong'... it's just that in this case Newton contributes more to the lift of the wing than does Bernoulli...

[Bert]

Did you type what you meant to type, Clanad? Surely the upper side of the wing of an aeroplane pushes the air up, and the lower side pushes the air down (because the wings on most aircraft slope downwards from front to back).
I have never understood that diagram they always show of air flowing over an aerofoil, where the air above has to take a longer route, because of the curvature of the upper side. As the route is longer, the air has to flow faster, they say. But how does the air above the wing know it has to meet up again at the trailing edge of the wing with the air from below the wing that it was separated from by the leading edge of the wing? Why doesn't it just flow at the same speed as the air below the wing, and meet up with air that was a few centimetres behind it before the wing ripped through?

[Canary42]

Surely by your explanation Clanad, I should be able to walk on water because my weight thrusting downward on the water is greater than the weight of air thrusting downward on my head, so the corresponding opposite reactions should ensure I don't move downwards ! ! ! !

Or have I missed something ?

[Clanad]

Apologies for not revisiting the thread earlier...

Bert has hit the nail squarely with his/her question about the body of air meeting again at the trailing edge of the wing. Of course it doesn't.

Look, until approaching supersonic speeds, the wing moves through the body of air and, since as already observed, the top of the wing (air foil, technically), being curved (to a greater or lesser degree, depending on the manufacturer) the air following this curved path is accelerated and as it leaves the top of the wing at the trailing edge, the accelerated air is less dense as well as moving faster than the body of air on the underside. This of course is the basis of Bernoulli's Principle.

However, the result is the body of air being acclerated can be accentuated or increased by lifting the leading edge of the wing causing an increased angle of attack which is the angle of the wing as a whole when measured against the body of air through which it is passing. The increases the accelration of air off the trailing edge and thereby creates lift, which action is Newtonian. This 'angle of attack' can only increase though, to around 10 or 12 degrees before the air next to the skin of the upperside pulls away and becomes turbulent, reaching the "stall" angle and resulting destruction of lift.

Interestingly enough, the aircraft designed by the Wright brothers had no curvature of the wings upper surface, but relied entirely on the changing angle of attack to produce the lift. This is also truely demonstrated by the paper airplane one makes as well.

I hope this addresses the question posed by Canary42 as well...