Re: You are skydiving, open a soda, does the liquid remain in the can?

Greetings:

Skydiving approaches the condition of weightlessness experienced by 
astronauts in orbit. However, as a free-falling skydiver picks up speed 
the upward force from the resistance of the air on the body increases until 
it equals the downward force from gravity. At this velocity, known as the 
TERMINAL VELOCITY, the skydiver travels weightless at a constant velocity a 
bit greater than 320 km/sec (200 mph). You might want to look up the exact 
terminal velocity for a falling human body. Soda is placed in cans under 
pressure from  carbon dioxide gas. When the can is opened it is likely that 
the carbon dioxide gas would spray the soda out of the free falling can in 
a manner similar to what happens when you shake a soda can before you open 
it while standing on earth. When the soda leaves the can the rushing air 
would disperse it upwards. Also, any soda remaining in the can will not 
pour out; you will have to shake it out! 

A second question might be, "How do you swallow the soda during free fall?"
First you had better put your mouth over the open can quickly to catch the 
spraying liquid. Then you might ask "can a free-falling person swallow a 
liquid inside their mouth without the effect of gravity?"

There is an extensive discussion on "The Effect of 
Weightlessness on the Human Organism" published by NASA 
here.

See the paper for detailed information. The bottom line from the paper is 
the following:

"How does the absence of gravity affect the human organism? 
The experience during free fall shows that a state of weightlessness 
lasting only a short time is not dangerous to one's health.
Whether this would be true in the case of long-lasting weightlessness, 
however, cannot be predicted with certainty because this condition has not 
been experienced by anyone. Nevertheless, it may be assumed with a high 
probability, at least in a physiological sense, because all bodily 
functions occur through muscular or osmotic forces not requiring the help 
of gravity. Actually, all vital processes of the body have been shown to 
be completely independent of the orientation of the body and function just 
as well in a standing, a prone, or any other position of the body. "

Best regards, your Mad Scientist

Adrian E. Popa

Admin note:
Gareth Evans adds the following:

I don't know the answer to the question but my guess is different from the
responder's.  My objections are more about some of the implications of
what was said.

1)  "the skydiver travels weightless at a constant velocity"
In fact the sky diver is only "weightless" at the start of the fall where
the effect of gravity is unopposed.  As the speed rises the diver is
subject to a force from wind resistance which build up until the force
equals his weight.  At this point his speed is constant but he is not
weightless.  The experience must be very different from that in a
free-falling aircraft or orbiting space-station.  In these cases the body
is accelerating towards earth.  It is that acceleration which keeps the
space station in orbit and not flying off at a tangent to the orbit.
Weightlessness is a condition when there is either no gravity or the force
of gravity is unopposed.

2)  "You might want to look up the exact terminal velocity for a falling
human body".  This implies there is an exact terminal velocity whereas the
number he gives is a good guide and the actual velocity depends on the
body and further, the attitude of the body.

3)  "the gas would spray out of the free-falling can"
The implication is that the fact that the can is free-falling means that
the pressure outside the can is sufficiently different to make the CO2
expand and expel the liquid.  The is no mention of aerodynamics, which is
needed to explain the gas expansion if indeed it is sufficient to expel
the liquid if indeed is happens.  The pressure above the falling can would
be lower than below due to the speed of the fall.  Whether that pressure
is low enough for the gas to behave as suggested is questionable at least.
My guess would be that the liquid would stay in the can unless the
buffeting shook it out.

I'd love to find out!

Here's a modified version of the answer:

Skydiving approaches the condition of weightlessness experienced by
astronauts in orbit when the diver steps out of the 'plane. However, as a
free-falling skydiver picks up speed the upward force from the resistance
of the air on the body increases until it equals the downward force from
gravity. At this velocity, known as the TERMINAL VELOCITY, the skydiver
travels at a constant velocity a bit greater than 320 km/sec (200 mph).
The terminal velocity depend on the shape, density and attitude of the
body.

When the can of soda is opened, assuming to opening is on top, will the
liquid escape?  If it was just water in the can the answer would probably
be no.  The only reason to suppose that it should would be because the
buffeting of the air at this speed may shake the can about.  If the liquid
is soda with CO2 dissolved in it under pressure, the situation could be
different.  It is the difference in pressure between the lower side of the
falling body and the upper side which provides the force which opposes the
weight of the body and keeps the body from continuing to accelerate.  The
pressure above the can will be lower than below and lower than normal
atmospheric pressure.  However, it may not be low enough to cause the gas
on the soda to expand sufficiently quickly to force the liquid out of the
can.  My guess is that it would not.  Why don't you try it?  I won't !