ABSTRACT
Chemists talk about moles and weighing moles. Physicists speak of charge-carrying wires and cutting field lines. What if they really meant what those names imply? John Holden helps us visualize that.
Units and dimensions are constant bugaboos for physics students. They are used to distinguish numbers which represent measurements of different things. Students learn that one mustn’t add numbers with different units, such as length to mass. That would be akin to adding apples and oranges, which would, however, be
o.k. if one only wanted to count pieces of fruit. One may multiply different units, and the results are in still different units. Work is the product of distance and force. If these have units of feet and pounds, the work has the unit ‘‘foot-pound.’’ But a quite different concept, torque, is also the product of a distance (lever arm in feet) and a force (in pounds). This, however is a vector, while work is a scalar. To distinguish one from the other, and keep everything perfectly clear, torque is given the unit ‘‘pound-foot.’’
