Re: How long can a straw possibly get so that you can still suck liquid from it

Okay, let's make the question a bit more interesting. Let's say your friend
handed you a straw that was 10 meters long and bet you $20 that you
couldn't finish an 8 oz. glass of apple juice. Would you accept the bet?

The answer involves the use of Bernoulli's equation:

	p1 + (1/2)*r*v^2 + r*g*y1 = p2 + (1/2)*r*v2^2 + r*g*y2


g is the gravitational constant (9.81 m/s^2) and r is the density
of the juice (for this problem I'll assume it's 1 g/cm^3 -- the same
as water)

y1-y2 is the height of the straw

p1 and p2 are the pressure on the juice at the bottom and top 
of the straw

v1 and v2 are the speeds of the juice at the bottom and top 
of the straw (let's say you drink very slowly, so we will ignore
these two terms)
 
The equation now reads

	p1 + r*g*y1 = p2 + r*g*y2

or

	p1-p2= r*g*(y2 - y1)

or 
	p1-p2 = r*g*h

where h is the height of the straw. If we assume that the difference in
pressure between the top and bottom of the straw is equal to the
atmospheric pressure at 20 degrees Celsius ( p(atm) = 101.3 kPa ) then
we get a height for the straw of 

	h = 10.3 m

So 10.3 meters is the maximum length of a straw. Does this mean you should
accept your friend's bet? Well, not really. Even though it's possible to
raise a column of water 10.3 meters, I think it would be impossible for a
person to do this with his or her lips. It would require the aid of a
mechanical pump.

Thanks for asking the question. Now I have one for you to think about:

What would happen if you tried to raise a column of water higher than 10.3
meters?