Re: Conservation of angular momentum

On May 26, 4:28 am, Mark Teller <markteller2...@xxxxxxxxx> wrote:
I guess this must be a trivial question.
Nevertheless I am having trouble with it.

Say there are two bodies in motion approaching each other. One of them
is a ball and another of a dumbbell shape. Both of them are in pure
translation with no rotation about any axis.

As the ball hits one end of the dumbbell it (dumbbell) starts
spinning.

How would you account for the fact that there was no net angular
momentum before collision, while there is after the collision?

Mark

Your problems with angular momentum are due to the fact that it is now
generally (incorrectly) considered to be something different from
linear momentum (different units, different dimensions, one is a
vector, the other is not). In fact, they are the same thing, and, for
a particle, it is equal to mv; linear and angular momentum readily
convert into each other (there are many examples of this). The
direction of the velocity of an object in rectilinear motion does not
change, of course, and the direction of the velocity of a point
object in curvilinear motion changes continuously. In either case, if
no net external force acts in the direction of its motion, the
magnitude of its momentum |mv| does not change. In the case of
extended objects, since they are all made of point particles, their
total momentum (linear or angular is the sum of the momenta of their
constituent particles. I hope this helps. If you have any questions,
please do not hesitate to ask.

Peter

.

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