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Re: Basketball and Global Warming

Science (AAAS) a few years back reported as a result of a rather extreme
"El Niño" the earth had slowed (detectable using the newer clock
technology (cesium?) after the El Niño had "passed" the earth's rotation
was back to "normal".

bc, who thinks the expansion of the oceans due to global warming will do
the same.

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. ;-)

Rick

****************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
rtarara@saintmarys.edu

**********************************************************
FREE: Windows and Mac Instructional Software
www.saintmarys.edu/~rtarara/software.html
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[Original Message]
From: Jack Uretsky <jlu@HEP.ANL.GOV>
To: <PHYS-L@lists.nau.edu>
Date: 12/30/2003 3:42:17 PM
Subject: Re: Basketball and Global Warming

But the analysis is still flawed. Steve leaves out the dynamics of
slowing the ball on the rebound.

On Mon, 29 Dec 2003, Steve Clark wrote:



When the ball started back down, wouldn't the earth have to begin to
move back toward the ball to conserve linear momentum? Thus, no net
change in the center of mass of the earth/basketball system. But don't
let the newspapers get wind of this problem. They'll get it wrong and
soon we'll be crashing into the sun "within the year'!

Steve Clark

On Monday, December 29, 2003, at 12:57 PM, Gary Turner wrote:



A nice easy puzzle for the holiday season - I was reminded of this by
the
recent conservation of (angular) momentum discussions. I have used it
in
the past to demonstrate the problems of assuming linear momentum is
only
conserved in "collisions" (whatever they are).

Consider a basketball, about to hit the ground. I has linear momentum
downward. A short while later, the ball will be moving up. It now


has


linear momentum upwards. Where did the downward momentum go? Well
that
one is easy, into the ground - but that means the ground is now moving
down.

Now, bounce a ball over and over, and eventually, the ground will


start


moving down at an appreciable speed. This is where basktball and
global
warming come in. Most basketball games are played at night. It does
not
matter where on the world you are, night is always on the opposite
side of
the Earth to the sun. So basketball games must be pushing the Earth
towards the sun - hence global warming.



--
"Don't push the river, it flows by itself"
Frederick Perls