Temperature Scale

Many people often think of temperature and heat as being the same thing. Temperature is a measure of the internal energy a substance has, while heat refers to the flow of internal energy from one substance to another. For instance, in a home during winter, there is a heat loss to the outside, which must be replenished in order to keep the temperature of the house constant. The processes by which heat energy is transferred from one object to another will be discussed later. In general, however, energy transfer can happen by one of three processes. Light can be absorbed or emitted (radiation), neighboring atoms can bump into matter (conduction), or matter can move from one place to another (convection/advection).

The energy of a rigid body in motion is generally given in terms of its mass and velocity. When we look closely at a substance at the atomic level, we see atoms and molecules vibrating and moving about at high speeds. We can associate that internal movement with the internal energy of the substance. The property of the substance that we associate with this internal energy is called the temperature.

The two most common units used to measure temperature are the Fahrenheit and Celsius scales. Both operate by defining two fixed points and making equal divisions between the two. The Fahrenheit scale sets the temperature at which water freezes at standard atmospheric pressure at 32^oF and the temperature at which water boils at standard atmospheric pressure as 212^oF. The Celsius scale uses 0^oC and 100^oC.

As the temperature is a measure of the amount of internal vibration within a substance, it should have a lowest possible value, which is the point at which all internal motion ceases. This temperature is refered to as absolute zero, and has been theorized to be -273.15^oC, or -459.67^oF. The Kelvin temperature scale uses absolute zero as the zero point for a temperature scale, and uses the same unit of division as the Celsius scale. Thus, on the Kelvin scale, water freezes at a standard atmospheric pressure at 273.15 K. Notice that no ^o symbol is used in the Kelvin scale. The unit of temperature in the Kelvin scale is kelvins, not degrees Kelvin.

Less often used is the Rankine scale, which is a temperature scale with a zero point of absolute zero, like Kelvin. The difference between the Rankine and Kelvin scales is that a temperature change of 1 Rankine is equal to 1 degree Fahrenheit.