The student will:
- Explain what is meant by temperature.
- Use the centigrade (Celsius) and Kelvin temperature scales.
temperature: A measurement of the average kinetic energy of the molecules in an object or system.  Temperature can be measured with a thermometer or a calorimeter.
Objects that appear to be motionless with the human eye still have motion inside them.  Matter is typically found in three states: solids, liquids, and gases. Solids have their molecules rigidly bound together by electrical forces, but the molecules can still vibrate back and forth in place. Liquids have molecules that touch and attract each other, but can move freely around each other.  Gases have almost no electrical attraction between their molecules, and can move freely in any direction.
The Fahrenheit Scale
The first modern thermometer was invented by Daniel Fahrenheit (1686-1736), shown in the Figure below. The Fahrenheit scale is common in the United States but rarely used elsewhere.  The scale was originally based on the range between zero at the temperature of brine (an equal mix of ice, water, and ammonium chloride) and 100 at average human body temperature.
The average is closer to 66.6 degrees above freezing (98.6 degrees). Since the freezing and boiling points of water make for good references, they were kept, and the average human body temperature was readjusted.
The Celsius Scale
The Kelvin Scale
The other metric scale was invented later, after it was determined that temperature is based on motion.  William Thomson, titled Lord Kelvin (1824 - 1907), Figure below, was an Irish physicist and engineer who devised a temperature scale that had an absolute zero.  Although he did not fully understand the nature of heat, his calculations predicted there was a minimum temperature where the object had absolutely no heat.
Check Your Understanding
1. What is a temperature of 20 °C in Kelvin?
2. What is the temperature of -300 °C in Kelvin?