Physics: Understanding the Properties of Matter and Energy

Physics: Understanding the Properties of Matter and Energy — page 9
PHYSICS UNDERSTANDING THE PROPERTIES or MATTER AND ENERGY heated to very high temperatures before it becomes a liquid or a gas In most people's experience wide changes in pressure are not as common as drastic changes in temperature For this reason examples of the effects of pressure on the states of matter are not common Often high pressure machines and vacuum low pressure machines must be used to study the effects of pressure changes on matter Under very low pressures matter generally tends to enter the gaseous phase At very high pressures gases tend to liquefy and liquids tend to solidify In fact at the very lowest temperatures that can be reached helium will not solidify unless a pressure of some 25 times the normal atmo spheric pressure is applied The relation between pressure and temper ature in changes of state is familiar to people who live at high altitudes There the pres sure is lower than at sea level so water boils at a lower temperature Cooking anything in water takes longer on a mountaintop than at sea level These properties of the three states of mat ter are easily observed They are ex exDlained however by a theory that describes the behav ior of particles far too small to be seen 14