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Re: Pb




On Fri, 09 Mar 2001 11:52:33 -0700 Jim Green <JMGreen@SISNA.COM> writes:
> Suppose I drop a piece of lead. The Earth, via gravity, does positive
> work on the lead and increases its KE.  OK?  The lead hits the floor; the
> floor does negative work on the lead; the lead halts. KE->0  OK? Does
> Wgravity = Wfloor?      Why is the lead heated?
 
 
I assume that your "W" above stands for Work rather than Weight.
Unlike forces, which are vector quantities, work is a scalar quantity
which has no direction and cannot be considered as either positive or
negative . .....   that is unless you define  the work as being positive when
energy is being added to a system... and work  being negative when
a system   gives us energy to its surroundings.
 
When you drop a piece of lead,  the lead and the Earth move toward
each other .  As they get closer and closer, the lead-earth system
loses potential energy, both the lead and the earth gain kinetic energy,
and the air , the lead, and the earth all become a bit warmer.
 
When the lead reaches the earth,  the remaining kinetic energy of the lead-earth
system is changed to "heat" energy and "sound" energy. Some this heat energy
raises the temperature of  both the lead and the earth. Some of it heats the air and
some of it radiates out into space.
 
If we assume that the "floor" is attached to the earth, the same kind of thing that
befalls the earh will also befall the floor.
 
 
 
> Please state any assumptions in you reply.
>
>
>
> Jim Green
> mailto:JMGreen@sisna.com
> http://users.sisna.com/jmgreen
>
 
 
Herb Gottlieb from New York City
(Where it's nice to live but I wouldn't
want to be a tourist here)
herbgottlieb@juno.com