Heat and Thermal Energy
Name: Neil S.
What is the difference between heat and thermal energy?
As loosely used, I think the two are equivalent.
The first law of thermodynamics divides the internal energy change of a
system, denoted, dE as the sum of the heat input/output, denoted dq, and the
work input/output, denoted, dw. So,
dE = dq + dw
where, inputs are positive and outputs are negative. In this sense one might
define the thermal energy as dE and the heat as dq. However, in common usage
I don't think that distinction is made.
There is no difference between "heat" and "thermal energy." They are
synonymous. Both refer to the net energy that is transferred form a hot object
to a colder one solely as a result of the temperature difference between
The word "thermal" in "thermal energy" is used to differentiate this type of
energy from other types, for example, kinetic energy, potential energy, etc.
Heat is a more familiar term. It has historically been used to refer to
that invisible "flow" that leaves us with the sensation of warmth. It was
later established that heat was a form of energy, and the expression "thermal
energy" was used to differentiate it from other forms of energy as stated
Ali Khounsary, Ph.D.
Advanced Photon Source
Argonne National Laboratory
Over zero degrees Kelvin, there is movement.
The temperature is a measure of this kinetic energy,
called thermal energy.
If two bodies with different temperatures are brought
together, than the movement of one body will influence
the movement of the other one and - after a period of time -
both bodies will be at the same level movement. Lord Kelvin pointed
out the direction of this flow of energy ( from the body with the
highest to the body with the lowest temperature ).
This flow of energy between two bodies at different energy
is called "heat". A body alone, considered as an unity, has
no "heat" : has thermal energy.
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Update: June 2012