Ain't Fiziks greit! :)

[Igor Kessel <e6941tb@ix.netcom.com>]

Fellows,
I thought I would succeed in staying away from this debate, but now I feel
compelled to add my two kopeks:

<<<<<<<<<<<<<<<<<<<<<<<<<<<<
a) Gases and liquids are NOT the same thing.

The matter exists in 5 states, depending on temperature.
1.  SOLID STATE. Constant volume, constant shape. Rigid crystalic grid
structure.
2.  LIQUIDS. Constant volume, inconstant shape. Non-rigid molecular
structure.
2a. AMORPHOUS STATE. Constant volume, inconstant shape. Non-rigid molecular
structure. Technically it's a LIQUID despite its seeming similarity to
SOLID STATE. Example - glass.
3.  GASES. Inconstant volume, inconstant shape. Non-rigid molecular or
atomic structure.
4. PLASMA. Inconstant volume, inconstant shape. Non-rigid structure,
comprised of free electrons and nuclei.

The main difference between a liquid and a gas is that the former is
(almost) non-compressable.

<<<<<<<<<<<<<<<<<<<

b) An aerofoil lifts according to the Bernulli Law:
-In a gas or a fluid the Pressure of flow is a reciprocal to its Velocity.

If you look at a crossection of an aircraft wing you'll notice that the
bottom is flat whereas the top is curved like a bow. According to Newton
there's no difference between a wing moving through the stationary air and
the stationary wing being being blown upon by the oncoming airstream.

When the wing cuts through the air, the air stream divides. One portion
passes the wing on the bottom side, the other half - on the top.

The velocity at the top portion is higher than it is at the bottom. If it
were not so the top portion would've lagged in relation to the bottom one,
hence creating a void, which is not possible.

Since the velocity at the top portion is higher than it is at the bottom,
according to the Bernulli Law the pressure from the faster top airstream
down onto the wing is lower than that of the slower bottom stream up
towards the wing. Once this Delta P exceeds the weight of the aircraft, we
get a lift-off.

Some other manifestations of the Bernulli Law:

1. A "Dry Leaf" kick in football*. When a player stands in the same line as
are both poles of the gates and kicks the ball while spinning it about its
vertical axis. For all non-Europeans on the list: a skilled  football
player can make a ball fly into the gates via a horisontal parabola,
fooling the goalkeeper. Hence the *Dry Leaf* term for the trajectory.

*By football I mean the World (real) football, where they actually use both
the "foot" and the "ball" in the game :)

Consider the equator of the spinning ball, which is flying towards you,
while spinning clockwise about the vertical axis.
On the left side the vector of air velocity coinsides with the tangential
vector of angular velocity of the rotating ball. The resulting vector of
air flow velocity on the left side of the equator is the momentary
difference of the said vectors.
On the right side the vector of air velocity is opposite to the tangential
vector of angular velocity of the rotating ball. The resulting vector of
air flow velocity on the right side of the equator is the momentary sum of
the said vectors.

It is obvious that the scalar values of the left side vector is lower than
that of the right side. Now the Bernulli Law kicks in: the Pressure from
the left side is higher than the Pressure from the right side.The resulting
Delta P forces the ball to move horisontally to the right, hence forcing it
to pick a complex parabolic trajectory.

Other examples of the Bernulli Law at work:
- an air brush principle
- a boomerang
- a famous Queen Mary ship wreck in the narrow strait
- yes, the Bernulli disk drive. It spins so fast that the disk gets sucked
to the read/wright head.

In the old days when I would hit the subject of Dinamics of Fluids and
Gases in the lectures, I would demonstrate my favourite example with a
ping-pong ball and a shop vac.

I would switch it to the blowing mode, point the tube up and ask my
students:
-what's gonna happen if I throw this light plastic ping-pong ball into the
stream of roaring air?
They would answer:
-it will fly all over the room.
I would throw the ball into the air stream and it would hang dancing in the
air in the middle of the room as if it were attached by an invisible string
to the invisible pipe.

I hope I did not bore you too much with this nerdy stuff. Sweet nostalgic
memories.

Mandatory Audi content: the faster I drive my 200, the more it gets sucked
down to the pavement, becoming more and more stable.

Let's just hope that my next Road Revenue Collection Agent would be able to
tell Bernulli from Raviolli. :)

--
Igor Kessel

~the SIG. line is also left blank intentionally~