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ERIC Number: EJ891999
Record Type: Journal
Publication Date: 2007-May
Pages: 4
Abstractor: As Provided
Reference Count: 5
ISSN: ISSN-0031-921X
Some Interesting Thermodynamics of the Thermos Flask
Berger, Roland
Physics Teacher, v45 n5 p270-273 May 2007
When opening a thermos flask filled with coffee, one often "hears" the equalization of the pressure difference that appears to be present between the air cavity inside the flask and the surrounding room atmosphere. Recently we discussed this phenomenon while drinking coffee and guessed about the direction of the gas stream accompanying the pressure release. Our hypotheses were tested, and we found that the pressure was higher inside the flask. But this only holds when the coffee is fresh. After some hours one observes an inversion; the pressure inside drops clearly under the environmental value and we wondered--what is going on inside the flask? That question gives the opportunity to discuss some basic thermodynamic concepts, with different degrees of difficulty, in a motivating manner.
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A