Originally Posted By: paul
Quote:
In thermodynamics, a closed system can exchange heat and work (for example, energy), but not matter, with its surroundings.


momentum , thermodynamics , n such

so you were saying something?


Yep, that momentum in a closed system cannot change - a point which wikipedia does not contest either in the page you cite, or in its page on momentum:

"Momentum is a conserved quantity, meaning that the total momentum of any closed system (one not affected by external forces) cannot change"

http://en.wikipedia.org/wiki/Momentum

Quote:
...some people have been able to prove that their sneeze traveled supersonic (breaking the sound barrier)


Two point here:

1) I can find no evidence to substantiate your claim. The maximum speeds I've found in various sources - medical and layman is 90-150mph. The fastest speed I've seen claimed by a pseudo-medical source (JFK Health World Museum) is 650mph; about 85% the speed of sound. According to wikianswers, the highest confirmed speed is 166.7km/h; about 103mph.

2) Even if your claim is true, it hardly disproves what I said. Your nose is a divergent structure; the nasal cavity expands in cross section nearly 15X relative to the nasopharinx (where the air enters the nose when you exhale/sneeze). Ergo, your nasal cavity acts exactly like a rocket nozzle would - it allows for acceleration of expired gas, due to the expansion of pressurized gas within the nasal cavity.

In fact, airflow through the nose is a serious area of research, and is very well understood. A few examples:
http://www.springerlink.com/content/x48u517p27517169/
http://www.springerlink.com/content/7869gchy3g05fhut/

Once again, the very physical phenomena I've been describing, in action...well understood, and completely within the laws of physics I have described.

Bryan
_________________________
UAA...CAUGCUAUGAUGGAACGAACAAUUAUGGAA