Energy is a fundamental physical concept
which can be used to interpret many everyday phenomena.
There are many forms of energy. Here are just a few examples:
An object has more energy when it is moving ("kinetic
energy"). Kinetic energy also depends on mass, so that
heavy objects have more kinetic energy than
light ones do, if they are moving at the same speed..
A book on a high shelf has more energy than when it is
on the floor ("gravitational potential energy"). Gravity energy also
depends on the weight of the book.
A hot object has more energy than when it is cold
("thermal energy").
Light delivers energy
("radiant energy").
A chemical fuel (such as coal or gasoline) releases
energy when it is burned ("chemical energy").
Energy can be converted from one form to another; however,
the total amount of energy in the universe does not change.
We say:"Energy is conserved," and refer to
this idea as the Principle of Conservation of Energy,
or even The First Law of Thermodynamics
(with these two grandiose names it must be important!).
Temperature and energy
We will have much to say about these subjects, and so it is important
to have them clearly defined.
Energy is what we add to a battery when we charge it. A moving hammer has more
energy than a stationary hammer; a hot pan contains more energy than a cold one.
We add energy to ice to melt it. Energy has many forms, but the total amount
of energy in the universe never changes.
Temperature is an indicator of the presence of a certain kind of energy.
However, we need to know other things before we can turn a temperature
measurement about a statement about energy: both the amount of material and the
kind of material matter. There is far more energy in a cold lake than in a
cup of hot coffee, just because there is far more water in the lake.
Heat is Thermal Energy
A hot object has more energy than when it is cold.
The extra energy is called "thermal energy." It is in the form of
small scale motions of the matter -- you may think of atoms running
around faster. The higher temperature may be the only indicator
of its presence.
Another word for thermal energy is "heat"; however, what we mean by "heating"
something is slightly different (only the energy that moves counts), and
in ordinary language we complain about the heat (but we are referring to the temperature,
which is not at all the same thing).
"Heat" is a confusing word;
just to be extra clear, we will never use the word "heat" at all.