The Nobel Prize in Physics 1996
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Phases and phase transitions |
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| Depending on
pressure and temperature, a substance can exist in
three phases – as gas, liquid or solid.
Water for example exists as steam, water or ice. The
transition between phases may be noticed as abrupt
changes in pressure and temperature. At normal pressures both 4He and 3He refuse to freeze no matter how low the temperature. The explanation is that no atoms can be completely at rest (zero point motion) and that the attractive force between helium atoms is too weak to make them come to rest. However, if the pressure is increased to about 3 MPa (30 atmospheres) both fluids become solids at very low temperatures. |
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