232 Chapter 9 Mass and Mass-Related Parameters
Atoms are combined naturally, or in a laboratory setting, to create molecules. For ex-
ample, as you already know, water molecules are made of two atoms of hydrogen and one
atom of oxygen. A glass of water is made up of billions and billions of homogeneous water
molecules. Molecules are the smallest portion of a given matter that still possesses its char-
acteristic properties. Matter can exist in four states, depending on its own and the sur-
rounding conditions: solid, liquid, gaseous, or plasma. Let us consider the water that we
drink every day. As you already know, under certain conditions, water exists in a solid form
that we call ice. At a standard atmospheric pressure, water exists in a solid form as long its
temperature is kept under 0C. Under standard atmospheric pressure, if you were to heat the
ice and consequently change its temperature, the ice would melt and change into a liquid
form. Under standard pressure at sea level, the water remains liquid up to a temperature of
100 C as you continue heating the water. If you were to carry out this experiment further
by adding more heat to the liquid water, eventually the liquid water changes its phase from
a liquid into a gas. This phase of water we commonly refer to as steam. If you had the means
to heat the water to even higher temperatures, temperatures exceeding 2000C, you would
find that you can break up the water molecules into their atoms, and eventually the atoms
break up into free electrons and nuclei that we call plasma.
Well, what does all this have to do with mass? Mass provides a quantitative measure of
how many molecules or atoms are in a given object. The matter may change its phase, but its
mass remains constant. Some of you will take a class in dynamics where you will learn that on
a macroscopic scale mass also serves as a measure of resistance to motion. You already know this
from your daily observations. Which is harder to push, a motorcycle or a truck? As you know,
it takes more effort to push a truck. When you want to rotate something, the distribution of
the mass about the center of rotation also plays a significant role. The further away the mass 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