Originally Posted By: paul
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"


...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:

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