Help! Physics Is Driving Me Nuts
Category: Science > Physics
Asked by: nronronronro-ga
List Price: $2.50
07 Nov 2002 17:45 PST
Expires: 07 Dec 2002 17:45 PST
Question ID: 102331
Feel kind of guilty placing a non-homework physics question on Google. On the other hand, I am an old man who is genuinely perplexed. My building is a 3-story concrete structure. Used to be a can factory. The walls, floors, and ceilings are solid concrete----approximately 18" thick. (Could never build something like this today. Would cost way too much.) Someone has drilled a 3" diameter hole in the floor of my third-story office. It goes down 18" to the ceiling of the guy below me on the second floor. The opening in his ceiling is also 3". Hence, the bored hole is of uniform 3" size and connects the two floors. When I place my hand near the 3" hole, I can detect very rapid movement of air. 24 hours a day. But I can't determine the direction! Is it cold air from my third-story office descending to the second-floor? Or, is is hot air from the second-story office rising? Both? I cannot determine either direction or temperature of the moving air by "feel" alone...and it's driving me nuts. The velocity is rapid---I am guessing 25 miles per hour. A great answer would be 3-4 sentences. Then I can sleep tonight... All comments greatly appreciated !
Re: Help! Physics Is Driving Me Nuts
Answered By: drdavid-ga on 08 Nov 2002 10:39 PST
If you have airflow at 25 mph (an exaggeration, I suspect, but I accept that there is at least a "strong" flow) through a "pipe" such as you describe, then the flow must be unidirectional, either up or down. Which it is depends on many factors, but I suspect that the dominant factor is the design of the air circulation system (heating and cooling system) in your building. A strong flow like you describe is probably driven by a pressure difference and not just a temperature difference, and the pressure difference is probably, in turn, determined by the configuration of ducts and blowers. It may also change from day to day or from winter to summer. If the flow bothers you, block it; if you want to know which direction its going, try holding a thin strip of paper or thread in the airflow and see which way it deflects (and you can always check the temperature with a thermometer). [Thats already five big sentences, which exceeds my quota, but Im a generous soul; if you need another sentence or a few of further discussion, just ask!]
rated this answer:
Top-notch answer. Thanks, Doc! Now I can sleep better...
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