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I am used to seeing and using...
L=r ×p = r × mv.
What happens when the object has:
v_y_ = +10
v_x_ = 0
And the original position of the object is (5,5) relative to my
origin. Then even though p is constant, the position vector r is
constantly changing in both magnitude and direction. In this case, L
is not constant. No torques, no interactions with something outside
of my system (the ball and my oddly chosen origin), and L is not
conserved. Why is that? There seems to be some sort of a condition
for the origin. I am not used to that. Thanks again for the time
help. Paul.
.:. Sent from a touchscreen .:.
Paul Lulai
-------- Original message --------
From: treborsci@verizon.net
Date:07/21/2014 1:05 PM (GMT-06:00)
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] angular momentum
Consider the motion of a ball, free of all forces, to be the constant
velocity path: x=a (a constant), and y= vt (v is its constant speed).
Its angular momentum about the origin (0,0) is simply m*a*v, a
constant in time. In the same way, Its angular momentum about any
fixed point is a constant in time .
Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
www.sciamanda.com<http://www.sciamanda.com>
-----Original Message-----
From: Paul Lulai
Sent: Monday, July 21, 2014 1:36 PM
To: Phys-L@Phys-L.org
Subject: [Phys-L] angular momentum
Hello.
I am finding I have some questions about conservation of angular
momentum that I hadn't considered in the past. If I am investigating
the angular momentum of a soccer ball about a point, is angular
momentum only conserved if the ball is orbiting about the center of a
circular path or a foci of an ellipse? Certainly a ball traveling
directly west across a field does not have its angular momentum
conserved. I am completely excluding the idea of impulse, torques,
and isolated systems at this point. I just found I haven't thought
about this aspect before. Thanks for your thoughts.
Paul.
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