Why airplanes taxi

On Feb 7, 8:39*am, Mxsmanic wrote:
terry writes:
The resistance is a function of the density of gas molecules not
pressure
density is related to pressure by
D=PM/RT
M=molecular wt
P=pressure
R=gas constant
T=temperature ( absolute )
ie the lower the temperature the higher the density
so what is the temperature in interestella space?

The classic gas laws only work when a volume of gas is contained.

Oh, Dear does that mean I cant really use the equation above for
calculating the air density in the atmosphere I am flying in?. Geez
its a wonder I havent killed myself. I will go and report myself to
CASA ( FAA equivalent downunder) today. I want my money back on
that phys chem degree I paid for too.
Terry
PPL Downunder

terry wrote:

The resistance is a function of the density of gas molecules not
pressure
density is related to pressure by
D=PM/RT
M=molecular wt
P=pressure
R=gas constant
T=temperature ( absolute )
ie the lower the temperature the higher the density
so what is the temperature in interestella space?

estimates are from between 3 - 20 K. But with Global Warming who knows.

On Feb 8, 8:15 am, terry wrote:

Oh, Dear does that mean I cant really use the equation above for
calculating the air density in the atmosphere I am flying in?. Geez
its a wonder I havent killed myself. I will go and report myself to
CASA ( FAA equivalent downunder) today. I want my money back on
that phys chem degree I paid for too.


:-)

Mxsmanic doesn't have to worry about taxying .
The power cord holds the computor desk down..

On Feb 6, 12:02 pm, Mxsmanic wrote:

But the original post said that aircraft taxi because their wheels reduce
friction. No mention of energy or force. So if the statement is true,
movement results from a lack of friction alone, so zero friction should
produce infinite speed (or lightspeed if one allows the speed of light as an
absolute upper limit).

However, space (especially near space) is not frictionless.

So, would having wheels reduce the friction in near space?

Dan

On Feb 6, 12:51*pm, Mxsmanic wrote:
writes:
Molecules

There aren't any molecules in space. *It's a hard vacuum.

You are wrong again. Read this; http://en.wikipedia.org/wiki/Outer_space

Ricky

wrote in news:69e5d860-7689-4422-94e6-66073069c012
@c4g2000hsg.googlegroups.com:

Fixed-wing aircraft taxi because their wheels reduce friction as they
move forward on the ground.

Fixed-wing aircraft taxi because the bus takes way too long.

Clark writes:

... it's not fair to pick on the incompentent...

Are you being facetious?

On Feb 8, 6:31*am, Gig 601XL Builder
wrote:
terry wrote:
The resistance is a function of the density of gas molecules not
pressure
density is related to pressure by
D=PM/RT
M=molecular wt
P=pressure
R=gas constant
T=temperature ( absolute )
ie the lower the temperature the higher the density
so what is the temperature in interestella space?

estimates are from between 3 - 20 K. But with Global Warming who knows.

yes, substitute 3 for T and 1 E-11 for P in the above equation, use
2 E-3 for MW ( any gas in interstellar space is likely to be
predominantly hydrogen, and you get 8E-16 kg/m3 for density, Very
small indeed, but then the resistance this provides to a spacecraft
is proportional to density. area. v squared.
when you chuck in a v that is anywhere near the speed of light and
square it, you start to get numbers that are no longer negligible.

So, logically, spacecraft in the frictionless environment of outer space
should immediately accelerate to the speed of light.


Some haphazard math here.. if space is indeed entirely frictionless,
which I highly doubt, then to accelerate a body of weight 1kg (2.2
lbs) to the speed of light (using a constant force of 1N (or 1 m/sec2
acceleration) would require a distance of 4.5*(10^16) meters or about
45000000000000 km which is about 300 billion miles. The work done/
energy needed would be about 450 trillion joules.
The time needed to achieve this feat would be about 9.5 yrs.. so no
its not instantaneous

wrote in
:

On Feb 6, 1:20 pm, Bertie the Bunyip wrote:
Mxsmanic wrote
:

writes:

Space isn't frictionless dummy.

Where does the friction come from?

Klingons, fjukkwit!

Bertie

So scrape them off dammit!


It's life Jim, but not a we know it!


Bertie