Poynting effect

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As Poynting effect , two by John Henry Poynting referred named phenomena of physics:

  • In continuum mechanics, this describes the change in length (expansion) of a cylindrical body under torsion , which John Henry Poynting observed on very long steel and copper cylinders and which leads to an increase in volume. This increase in volume indicates elastic dilatation and is theoretically a 2nd order effect in elasticity theory.
  • In thermodynamics , the change in the vapor pressure of a condensate due to mixing with a gas that is non-condensable in the pressure and temperature range under consideration is called the Poynting effect. For example, it plays a role in anesthesia when using Entonox (MEOPA) in pressure bottles. This is a 50:50 mixture of oxygen with the narcotic nitrous oxide ( "laughing gas" ). The oxygen in the pressurized cylinders is gaseous and the nitrous oxide is usually liquid, but due to the Poynting effect it is also in gaseous form.

These Poynting effects are to be distinguished from the Poynting-Robertson effect .

Individual evidence

  1. ↑ JH Poynting: On pressure perpendicular to the shear planes in finite pure shears, and on the lengthening of loaded wires when twisted. In: Proceedings of the Royal Society. A 82, 1909, pp. 546-559. In 1913, Poynting also examined the example of a twisted rubber thread JH Poynting: The changes in length and volume of an Indian-rubber cord when twisted. In: India-Rubber Journal. October 4, 1913, p. 6.
  2. ↑ Brockhaus abc Physics . 1st edition. VEB FA Brockhaus Verlag, Leipzig 1972.
  3. ^ Poynting effect. In: Ulrich Kilian, Christine Weber (Ed.): Lexicon of Physics. Spektrum-Verlag, 2000.
  4. ↑ Anesthesia General, Poynting Effect