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Re: [Phys-l] ? passive force of constraint



I think that John is asking about passive, as opposed to active, forces,
where an active force is a force exerted by an animate organism and a
passive force is a force exerted by an inanimate object. Not all
passive forces are forces of constraint. Gravitational and macroscopic
electrostatic forces are passive forces.

Many students in introductory physics courses believe that only active
forces exist. The following is a typical statement: "The table doesn't
exert a force on the falling ball: It simply gets in the way." Physics
education research has shown that addressing this preconception helps
many of these students to better understand normal force, tension and
other passive forces.


The terminology passive and active with respect to forces have appeared in
texts, and this is unwise, except in a refutational passage. Actually most
texts use the words action and reaction which students translate to mean
active and passive. I was in a school where the physical science teachers
were asking question on test like "which force is the reaction" with the
answer being the force which is identified by students as the passive force.
The school was supposed to be very good, and when I objected to things, I
was slapped down.

John M. Clement
Houston, TX