Have you ever thought about what the term temperature really means and how many ways it can be represented? A scientific definition is, temperature is an arbitrary measure which is proportional to the average kinetic energy of the molecules in an ideal gas. A more practical definition might be: temperature is the sensation we feel as warmth or cold. It can be extreme, like the heat of fire and ice, or moderate like the varying temperatures in a home. The measurement of temperature is very important for all sort of things like manufacturing processes, the safe storage of foods, and many other everyday items we might take for granted. There are four temperature scales commonly used in the United States. The two that most of us are familiar with are the Fahrenheit (° F) scale and the Celsius (° C) scales. Celsius was formerly called centigrade. In science and manufacturing, there are two other scales used. They are the Kelvin and the Rankine scales. How do these various scales relate to each other? There are several equations, which can be used to convert among the scales. To find degrees Celsius when you know the Fahrenheit temperature use this equation: °C = 5/9 (°F - 32) To find degrees Fahrenheit when you know the Celsius temperature use this equation: °F = 9/5 °C + 32 To find degrees in Kelvin when you know the Celsius temperature use this equation: °K = °C = 273.15 To find degrees in Rankine when you know the Fahrenheit temperature use this equation: °R = °F + 459.67 It is interesting to note that when a temperature is either °K or °R, it is said to be the absolute temperature, because these scales read zero for the condition where the kinetic energy of the molecules of an ideal gas is presumed to be zero. This means at 0°K or 0°R, all molecular motion stops. This is known as the term absolute zero.   The outside temperature in Nome, Alaska in December is -40° Fahrenheit. What is this temperature in degrees Celsius? °C = 5/9(-40°F - 32) = -40° Celsius A laboratory sample of a molten metal is measured at 2,100°C. What is the absolute temperature of this metal sample in degrees Kelvin? Estimate the answer: Less than 273 °K Between 273 and 2,100 °K Greater than 2,100°K