Matter exists in three states: solid, liquid, and gas;
each has distinguishing characteristics. Solids have
a definite volume and a definite shape; liquids
have a definite volume, but take the shape of their
containing vessels; gases have neither a definite
shape nor a definite volume. Gases not only take
the shape of the containing vessel, but also expand
and fill the vessel, regardless of its volume.
Examples of the states of matter are iron, water,
and air.
Matter can change from one state to another.
Water is a good example. At high temperatures
it is in the gaseous state known as steam. At
moderate temperatures it is a liquid, and at low
temperatures it becomes ice, which is definitely
a solid state. In this example, the temperature is
the dominant factor in determining the state the
substance assumes.
Pressure is another important factor that will
affect changes in the state of matter. At pressures
lower than atmospheric pressure, water will boil
and thus change into steam at temperatures lower
than 212° Fahrenheit (F). Pressure is also a critical
factor in changing some gases to liquids or solids.
Normally, when pressure and chilling are both
applied to a gas, the gas assumes a liquid state.
Liquid air, which is a mixture of oxygen and
nitrogen, is produced in this manner.
In the study of fluid power, we are concerned
primarily with the properties and characteristics
of liquids and gases. However, you should keep
in mind that the properties of solids also affect
the characteristics of liquids and gases. The lines
and components, which are solids, enclose and
control the liquid or gas in their respective
systems.
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