Temperatura
La temperatura es un promedio de la energía cinética de traslación de las partículas elementales de cualquier sustancia pura.[1]
Contenido
Definición conceptual
En condiciones normales, las partículas elementales de cualquier sustancia (átomos de un elemento químico, y moléculas de un compuesto químico) se mueven de forma aleatoria en cierta medida. Puesto que se mueven, tienen energía cinética.
Calor es el total de energía cinética que estas partículas tienen, o una medida de la transferencia de dicha energía de un cuerpo a otro. La temperatura es el promedio de esta energía y depende de la cantidad de sustancia presente.
Aplicación práctica
La temperatura determina donde el calor fluirá cuando dos objetos hacen contacto. El calor siempre fluirá desde el objeto que tiene la temperatura más alta para el objeto que tiene la temperatura menor. El calor no tiene un flujo neto entre dos objetos cuya temperatura es la misma.
Furthermore, if any two objects are each at thermal equilibrium with a third object, i.e. have the same temperature as that third object, then they must be in thermal equilibrium with one another. Ralph H. Fowler recognized this transitive property of thermal equilibrium as the Zeroth Law of Thermodynamics.[2]
Absolute Temperature
Absolute zero is the temperature at which all random motion of the elementary particles of a substance ceases. By definition, no substance can possibly be colder than this.
The absolute temperature of any substance is the difference between the measured temperature, on any given scale, and absolute zero.
Scales
Four different temperature scales are in common use today. Each one measures temperature with reference to one or more standard temperatures.
Fahrenheit
The Fahrenheit scale uses as its zero the freezing point of a supersaturated aqueous solution of sodium chloride. On this scale, the boiling point of water is 212 degrees.
Celsius
The Celsius or centigrade scale uses as its zero the freezing point of pure water. The boiling point on this scale is 100 degrees.
Kelvin
The Kelvin scale uses absolute zero as its zero. Its degrees describe the same interval as those on the Celsius scale, and therefore on this scale the freezing and boiling points of water are one hundred degrees apart.
Rankine
The Rankine scale also uses absolute zero as its zero. Its degrees describe the same interval as those on the Fahrenheit scale.
Conversions
To convert from Celsius to Fahrenheit, multiply the Celsius temperature by 9/5, and add 32, the Fahrenheit temperature of the freezing point of pure water.
To convert from Fahrenheit to Celsius, first subtract 32 from the Fahrenheit temperature and then multiply the result by 5/9.
To convert from Celsius to Kelvin, add 273.15 to the Celsius temperature. Absolute zero is 273.15 degrees Celsius below zero. (The Kelvin scale uses no degree symbol, and instead uses the letter K with no other symbol.)
To convert from Fahrenheit to Rankine, add 491.67 to the Fahrenheit temperature. Absolute zero is 459.67 degrees Fahrenheit below zero.
Referencias
- ↑ Jones, Andrew Z. "Definition of Temperature." <physics.about.com/>, n.d. Consultado el 26 de junio 2008.
- ↑ Jones, Andrew Z. "Laws of Thermodynamics." <physics.about.com/>, n.d. Accessed June 26, 2008.
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