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• Localización: Scientific American, ISSN 0036-8733, Vol. 290, Nº. 5, 2004, págs. 120-120
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • The article answer a question about measuring temperatures close to absolute zero and another on why air is cooler at higher elevations. Wolfgang Ketterle of the Massachusetts Institute of Technology, who won the Nobel Prize in Physics in 2001 for his work with ultracold atoms, explains: First, let me introduce the scientific meaning of temperature: it is a measure of the energy content of matter. Cooling requires extracting energy from an object and depositing that energy somewhere else. As an atomic cloud becomes denser and colder, the cooling effect becomes dominated by other processes, which still result in some trembling motion of the atoms. The processes include energy release from collisions between atoms and the random recoil kicks in light scattering. At this point, however, the atoms are cold enough to be confined by magnetic fields. Evaporative cooling can then selectively remove the most energetic atoms from the system. Paul B. Shepson, professor of atmospheric chemistry at Purdue University's School of Science, provides this answer: In the earth's atmosphere, pressure, which is related to the number of molecules per unit volume, decreases exponentially with altitude. Therefore, if a parcel of air from the surface rises (because of wind flowing up the side of a mountain, for example), it undergoes an expansion, from higher to lower pressure. When air expands, it cools.