Temperature , Heat and Heat Tansfer Illinois State 温度，热和传热伊利诺斯州.docVIP

Temperature, Heat and Heat Transfer When we think of temperature, we usually think of something that we measure with a thermometer. However, have you ever stopped to think about what you were measuring? Temperature is a measure of the kinetic energy of molecules and atoms in the surroundings. An environment where the molecules are moving around very quickly is said to have a high temperature. An environment where there is relatively small motion has a low temperature. This is how the Kelvin temperature scale was determined. We hopefully are familiar with the Celsius and Fahrenheit scales: Water boils: 100 degrees Celsius 212 degrees Fahrenheit Water freezes: 0 degrees Celsius 32 degrees Fahrenheit and 1 degree Celsius is 9/5 degrees Fahrenheit. So we can go back and forth between units of temperature. In equation form: TF = 9/5 TC + 32 Furthermore, as you can tell from the units of division, we will stick with the Celsius scale. The Absolute Temperature Scale The Kelvin scale was defined from the concept of absolute zero. Absolute zero is the theoretical point where all molecular and atomic motion stop (However, when you encounter quantum mechanics next semester you will find out that there is always some residual energy left over, this is known as the zero-point energy). It was found by looking at how the pressure in a gas reacts to falling temperature: The hypothetical negative pressure region cannot happen so there is a limit to how “cold” something can get. It was found to be –273 degrees Celsius. This was the 0 point for the Kelvin scale. So to find a temperature in Kelvin, you just add 273 degrees to the Celsius scale. Therefore: Water boils: 373 Kelvin Water freezes: 273 Kelvin Notice not “degrees” Kelvin! The Celsius, Fahrenheit and Kelvin scales were all named after the men who “discovered” them: Anders Celsius (1701-1744), Gabriel Fahrenheit (1686-1736), and Lord Kelvin (1824-1907), respectively. Temper