Diving Physics Puzzle

[Thalassamania]

Depends on whether you mean half deflate the balloon or compress the balloon somehow to half it's volume. As others say, balloons are elastic and pressure/partial pressure remains constant.

The question clearly states: "and you deflated it to half the volume."

 

[Tigerman]

Question then is, was the question based on the elastic being linear or was the non-linear elastic a part of the question given?

 

[beachegirl]

Thanks guys!
The answer that was given to me a few years ago when I taught this class...
deflation = partial pressure half of previous amount.
addition of air = increase of PO2 and decrease of PCO2

again not sure about this answer, but interesting.

Thanks all for your thoughts and comments.
If you think you know why this might be the correct reason... please post.

 

[knotical]

If you think you know why this might be the correct reason... please post.

Thalassamania gave you the answer. But since you’re looking for why, consider that the process of deflating and inflating replaces some of the original gas mix with another mix, presumably air, with less CO2 (hopefully zero) but more O2. A confusing factor is that there is a third gas in the original mix, presumably N2.

Assume normal atmospheric pressure of 760 mm Hg, and normal air consisting of 21% O2 and 79% N2 (plus trace gases). Thus air has approximately 160 mm Hg O2, as Thal mentioned.

Mix in balloon before:
O2 = 150 mm Hg
CO2 = 50 mm Hg
N2 = 560 mm Hg

Added air:
O2 = 160 mm Hg
CO2 = 0 mm Hg
N2 = 600 mm Hg

Mix in balloon after (averaging the above):
O2 = 155 mm Hg
CO2 = 25 mm Hg
N2 = 580 mm Hg

All three mixes add up to ambient pressure of 760 mm Hg.

The answer that was given to me a few years ago when I taught this class... .

Taught it or took it?

 

[beachegirl]

deflating and inflating replaces some of the original gas mix with another mix, presumably air, with less CO2 (hopefully zero) but more O2.

Great answer!

Much thanks!

 

[Blackwood]

I did not know that.

Not up on bubble mechanics much?

 

[pdelannoy]

You are describing Avogadros Law. Temperature and Pressure are constant. When you re-inflate to the original condition, T and P are still constant. The way this problem is described assumes V and n (moles) are variables.

PD

 

[Smiling Armina]

hmmm.

 

[dschonbrun]

fppf is right. In order to inflate a balloon, you must overcome the highest pressure/effort at the outset.

 

[tarponchik]

Actually, pressure inside a balloon will INCREASE as you deflate it. This is because the elastic is non linear and gets thicker and stronger as the balloon gets smaller.

Qite the opposite, because elastic is more stretched when the baloon is fully inflated. Wouldn't it be funny if letting the air out of baloon increased the pressure inside?