13.1. Temperature http://www.ck12.org
13.1 Temperature
Objectives
The student will:
- Explain what is meant by temperature.
- Use the centigrade (Celsius) and Kelvin temperature scales.
- Describe the relationship between temperature and kinetic energy.
Vocabulary
- temperature: A measurement of the average kinetic energy of the molecules in an object or system. Tem-
perature can be measured with a thermometer or a calorimeter.
Introduction
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.
Temperatureis a measure of the motion of the molecules of a substance. It is traditionally measured with a
thermometer, which uses a liquid that can readily expand and contract in a tube. As the liquid gets hotter, it expands
and shows a higher number on the tube. There are two closely related metric units of temperature – degrees Celsius,
◦C, and Kelvin, K, as well as the common non-metric unit, degrees Fahrenheit,◦F.
The Fahrenheit Scale
The first modern thermometer was invented by Daniel Fahrenheit (1686-1736), shown in theFigure13.1. 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.