ISSN:0002-9505    

DOI:10.1119/1.17784

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17786

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18056

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18057

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18063

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18058

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Temperature measurements taken near vessel walls show that initially hot water may well begin to freeze quicker than cold. This is not, as previously surmised, due to the cooling history of the water (e.g., air expulsion during heating). Rather, supercooling virtually always takes place. On those occasions where the cold water supercools sufficiently more than the hot the Mpemba scenario is the following: The hot water supercools, but only slightly, before spontaneously freezing. Superficially it looks completely frozen. The cold water (in larger volume than that of the hot sample) supercools to a lower local temperature than the hot before it spontaneously freezes. This scenario can occur more often for ambient cooling temperatures between −6 °C and −12 °C.

ISSN:0002-9505    

DOI:10.1119/1.18059

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

A full‐scale re‐enactment of an historic experiment carried out by Pascal in 1646 to demonstrate the principles of barometric pressure to an outdoor audience can provide a dramatic event today for a university open day or a town festival. The script for such a performance is given together with practical details for its production.

ISSN:0002-9505    

DOI:10.1119/1.18060

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Pressure melting cannot be responsible for the low friction of ice. The pressure needed to reach the melting temperature is above the compressive failure stress and, if it did occur, high squeeze losses would result in very thin films. Pure liquid water cannot coexist with ice much below −20 °C at any pressure and friction does not increase suddenly in that range. If frictional heating and pressure melting contribute equally, the length of the wetted contact could not exceed 15 μm at a speed of 5 m/s, which seems much too short. If pressure melting is the dominant process, the water films are less than 0.08 μm thick because of the high pressures.  

ISSN:0002-9505    

DOI:10.1119/1.18028

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

We describe an apparatus with which the shape, size, and composition of a concealed body are determined by measuring the body’s moments of inertia about its three principal axes. The apparatus is constructed using inexpensive, easily obtained materials and components. Just as in professional research, students must rely solely on their data to guide them to the correct answer. Response to the experiment has been very favorable.

ISSN:0002-9505    

DOI:10.1119/1.18029

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP