Re: Pb

["Bernard G. Cleyet & Nancy Ann Seese" <georgeann@REDSHIFT.COM>]

Chiming in -- the selection of Pb is fortunate as it can't be work hardened (at
RT).   As a result, another complication wa avoided.  The majority of other
metals and alloys can, and, therefore, some of that KE will be converted into
internal energy that is not "HEAT."  Upon annealing that energy will be
"released" as mostly heat.

bc



"John S. Denker" wrote:

> At 04:55 PM 3/9/01 -0500, Michael Edmiston wrote:
>
> > 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.
>
> What's wrong with the usual Physics 1 terminology?  I vaguely recall being
> assigned this problem back when I was in the larval stage.
>
> Object #1.  Mass M1.  Initially at rest.
> Object #2.  Mass M2.  Initial velocity V2.  Collides with #1 and sticks.
>
> P before = M2 V2.
> KE before = P^2 / 2M2
> P after = P before.
> KE after = P^2 / 2(M1 + M2) == really small if M1 = earth.
>
> > 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.
>
> Sure.  But if the floor doesn't deform, the transferred energy is really
> small, as I asserted in general terms earlier and calculated above.
>
> > 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
>
> The original problem set for us spoke of M2 being lead, and asked us to
> make explicit whatever assumptions we wished.  I explicitly stated that I
> wished to model the lead as being fairly squishy, and the floor as being
> reasonably rigid.  These conditions can be achieved in practice;  they are
> not absurd or unphysical.
>
> If you want, you can make the opposite assumption.  You can devise some
> super-hard lead alloy, and drop it on a marshmallow floor.  That wasn't how
> I interpreted the original question, but suit yourself.
>
> > 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.
>
> Ditto.  This is a just a question of how to interpret a somewhat vague
> question.  I still think the intent was to have the lead ball deform, not
> the floor, but you are free to assume otherwise.