This is a specific reply to John Denker, but others are welcome to chime in.
John wouldn't have used some of the wording I used. But I am curious as to
what wording to use when things are colliding and materials are being
deformed (permanently or temporarily) and kinetic energy is "being
converted" to thermal energy.
If the definition of work is basically F times delta-x (with the usual
integral stuff as necessary), isn't that happening with the floor and the
dropped object.
Clearly a third-law action/reaction pair exists. And clearly the force of
the ball on the floor is moving/deforming the floor a bit, and the force of
the floor on the ball is moving/deforming the ball a bit. The "delta-x" is
pretty small, but the impulsive forces are huge, so the work can still be
substantial.
Or do we typically not call this work? What do we call it when a force
permanently or temporarily deforms something?
I always viewed it as work just like we do work when we compress a spring.
And just like some springs and rubber bands are more elastic than others,
some of this compression/deformation work shows up as thermal energy due to
atomic/molecular friction.
I also don't understand why John says the floor doesn't gain much thermal
energy from this interaction. Doesn't it depend on what the floor is. If
the floor were covered with inelastic rubber floor mats I would think the
"floor" would gain more thermal energy than the ball.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817