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Introducing WORK



My students will start learning about work this week. As usual,
the product F*d is going to be called work and N*m is going to
be called Joule. In textbooks one can often see verbal formulations
referring to "work done on an object" rather than "work done by a
specific force on such object". I do not like this.

Suppose I am pushing a box along a horizontal floor with F=100 N
over d=2 m. There is no acceleration. Somebody could say "the work
done on the object is 200 J". The second person could object by saying
that a=0 implies a friction force and "the work done on the box is
zero, +200 J by the pusher and -200 J by the floor. And a third person
may consider a situation in which there is a positive acceleration. In
that case "the work done on the box can be anything between 0 and
200 J, depending on the size of acceleration.

The concept of energy is ahead of us and work can not be defined
thermodynamically at this stage of learning. Would you agree that
"the concept of work has no meaning unless a working force is
specified"?

Three years ago I heard about an elementary physics curriculum
(developed and presumably widely used in West Germany) which
teaches about energy before teaching about work. Work is then
defined thermodynamically, from the very first encounter. Can
somebody tell us more about this approach? Was it tried in other
countries? What is its present status? A good and accessible
reference (written in English) could be very helpful.

Ludwik Kowalski