308 Chapter 11 Temperature and Temperature-Related Parameters
example, as you already know, water molecules are made of two atoms of hydrogen and one
atom of oxygen. Temperature represents the level of molecular activity of a substance. The mol-
ecules of a substance at a high temperature are more active than at a lower temperature. Perhaps
a simple way to visualize this is to imagine the molecules of a gas as being the popcorn in a pop-
corn popper; the molecules that are at a higher temperature move, rotate, and bounce around
faster than the colder ones in the popper. Therefore, temperature quantifies or provides a mea-
sure of how active these molecules are on a microscopic level. For example, air molecules are
more active at, say, 50C than they are at 25C. You may want to think of temperature this
way: We have bundled all the microscopic molecular movement into a single, macroscopic,
measurable value that we calltemperature.11.2 Measurement of Temperature and Its Units
Early humans relied on the sense of touch or vision to measure how cold or how warm some-
thing was. In fact, we still rely on touch today. When you are planning to take a bath, you first
turn the hot and cold water on and let the bathtub fill with water. Before you enter the tub, how-
ever, you first touch the water to feel how warm it is. Basically, you are using your sense of
touch to get an indication of the temperature. Of course, using touch alone, you can’t quantify
the temperature of water accurately. You cannot say, for example, that the water is at 21.5C.
So note the need for a more precise way of quantifying what the temperature of something is.
Moreover, when we express the temperature of water, we need to use a number that isCopyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀