A study of the properties of matter must include a study of energy.
Energy,
defined as the capacity to do work, has many forms.
Potential energy is stored energy; it may be due to composition (the composition of a battery determines the energy it can release), to position (a rock at the top of a cliff will release energy if it falls to lower ground), or to condition (a hot stone will release heat energy if it is moved to a cooler place).
Kinetic energy is energy of motion. You are undoubtedly aware that the faster a car is moving, the more damage it does on crashing into an object. Because it is moving faster, it has more kinetic energy and has a greater capacity to do work (in this case, damage).
One of the characteristics of energy is that one form of energy can be converted to another. When wood is burned, some of its potential energy is changed to radiant energy(heat and light). Some is changed to kinetic energy as the water and carbon dioxide formed move away from the burning log. Some remains as potential energy in the composition of the water and carbon dioxide produced by the burning. Throughout all these changes, the total amount of energy remains constant. All changes must obey the
Law of Conservation of Energy, which states that energy can neither be created nor destroyed. An alternative statement is that the total amount of energy in the universe remains constant.
The Law of Conservation of Mass and the Law of Conservation of Energy are interrelated principles. Mass can be changed into energy and energy into mass according to the equation:
E=mc2
where
E = energy change
m = mass change (in grams)
c = speed of light (3.00 X 108 m/sec, or 186,000 mi/sec)
This relationship allows us to state the two laws as a single law, called the Law of Conservation of Mass/Energy:
Energy and mass may be interconverted, but together they are conserved. This law was first stated by Albert Einstein (1879-1955). In most changes, the amount of matter converted to energy is much too small to be detected by even the most sensitive apparatus, and we can say "in this change both mass and energy are separately conserved." It is nevertheless important to be aware of this relationship between mass and energy, because nuclear energy is obtained by just such a conversion of mass to energy.