Page 31 - Curriculum Visions Dynamic Book

water. As a result, the soap molecules and their captured dirt particles are pulled away from the surface to remain suspended in the water. Because it is now surrounded by soap, the dirt particle cannot readily settle out and stick back on a surface, so it is easily washed away.
A detergent is a material made from crude oil that mixes with water. Most detergents are more complex than soap because fabric or household surface cleaning needs to remove a complex variety of substances in addition to greasy dirt. However, they work in much the same way. That is why sometimes washing your hands with soap will not get them fully clean, but using a detergent, such as washing-up liquid, will.
Compressibility and hydraulics
Although the molecules in a liquid are free to move around, there is not much difference between the density of a liquid free to move around and one that is confined and under pressure. This is an important property that is employed when liquids are used to send forces from one place to another. If the liquid compressed, that would not be possible. Sending forces using a liquid is known
as hydraulic action. Water can be used in this way provided it is not expected that temperatures
above boiling point or below freezing point will be encountered. So, it is perfectly
possible to use water as a hydraulic fluid indoors, but it is not used in, for example,
the braking system of a car. That is because in winter the water might freeze, and under heavy braking pressure the heat generated in
the brakes might make the water boil.
(Above) Coloured water being used to demonstrate the incompressibility of liquid water and its ability to transmit forces if it is confined.
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