Physics: Understanding the Properties of Matter and Energy
PHYSICS UNDERSTANDING THE PROPERTIES or MATTER AND ENERGY and the explosion of a stick of dynamite all have one thing in common they are expres sions of energy Energy and matter together form the basis for all observable phenomena THE STATES OF MATTER Most of the matter that people ordinarily observe can be classified into one of three states or phases solid liquid or gas Solid solid gas ice water vapor liquid water cyclopaedia Britannica no Water exists in the three basic states of matter as ice water and vapor Encyclopaedia Britannica Inc 12
WHAT IS MATTER matter generally possesses and retains a def inite size and shape no matter where it is situated A pencil for example does not change in size or shape if it is moved from a desktop and placed upright in a glass A liquid unlike a solid assumes the shape of its container even though like a solid it has a definite size or volume A pint of water changes its shape when it is poured from a glass into a bowl but its volume remains the same A gas expands to fill the complete volume of its container At a given temperature and pressure a sub stance will be in the solid liquid or gaseous state But if the temperature or the pressure changes its state may also change At con stant atmospheric pressure the state of water for example changes with changes in tem perature Ice is water in a solid state If it is removed from a freezer and placed in a warm pan the ice warms up and changes to a liquid water If the pan is then placed over a hot fire the water heats up and changes to the gaseous state steam Most substances can exist in any of the three states provided that they do not decom pose chemically as sugar for example often does when it is heated in air Oxygen must be cooled to very low temperatures before it becomes a liquid or a solid Quartz must be 13
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
WHAT IS MATTER ATOMIC THEORY OF MATTER All substances are made up of tiny units called atoms Each atom consists of a massive positively charged center called the nucleus around which fly one or more negatively charged electrons The nucleus itself contains at least one proton a positively charged particle In all atoms except those of ordinary hydro gen the nucleus also contains at least one neutron a particle that has no electrical Hydrogen Atom Oxygen Atom One electron pink circles the lone proton blue in a hydrogen atom An oxygen atom has eight protons blue which can bind eight electrons Encyclopaedia Britannica Inc 15
