Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Basketball and Global Warming

I try to get students to look at these conceptual problems from a
variety of 'extreme' points of view.

For instance, let's say that the earth has a mass EQUAL to the
sum-total mass of the entire Chinese population.. Consider massless 1
meter high step ladders that each will climb.

Remember that the CM will ALWAYS be fixed in space unless there is
some external force.

Does that help the picture clear up any????

or try it with just ONE ladder climber and the earth's mass equal to hers.


At 4:08 PM -0500 12/30/03, Richard Tarara wrote:
The variation on this--If all the Chinese jump off a 1 meter high
step-stool at the same time.....

I have no problem with the conservation of momentum but have more of a
problem with the position part. I'm sure part of the analysis has to do
with the act of climbing up the stool steps, but what I have trouble with
is that the 'last' thing in the problem is the force of the feet hitting
the earth. We tend then to think of this force as one that would drive the
earth away from the feet. However, to conserve linear momentum and the
position of the COM, this force needs to STOP the earth from moving and
needs to stop the earth back at it's initial position (before the climbing,
jumping, and landing). I'm not sure I have all the motions straight in my
head, so I'll leave it for someone else to explain the whole thing in
detail! I suspect we need to look at the impulses (of the falling Chinese
on the earth versus their feet hitting the earth), but what about as they
climb the steps--moving farther away from the center of the earth and
pushing 'down' to do so. ;-)

--
Chuck Britton Education is what is left when
britton@ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 416-2762 Albert Einstein, 1936