Work and heat are both names for ways in which energy can transfer from one object to another.
Mechanical work occurs via large-scale fores between objects, in which one can keep track of the product of the force times the distance moved by the point the force acts on. Thatís the work, so long as youíre careful to use the vector dot product.
Heat is the energy transfer due to the temperature difference between the objects. At a very small scale, little particles are still exerting forces and doing work on each other, but not on a scale we can keep track of in detail.
You can probably think of energy transfers that donít neatly fit in either category, such as ones involving rubbing friction. Thatís no problem, we still understand whatís going on regardless of the words.
Note that heat and work are forms of energy transfer, not forms of energy. You canít correctly say that some object has a certain amount of heat or work in it.
(published on 08/03/07)