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Re: [Phys-l] interaction



While we are discussing various ways of stating the laws of
motion, let me remark that there is some difference of opinion
as to whether N3 should be stated in such a way as to incorporate
conservation of /angular/ momentum.

Some folks like to incorporate it; others state it separately.

Note that conservation of angular momentum by itself immediately
implies conservation of linear momentum ... but the converse does
not hold. Starting with conservation of linear momentum, you need
to add additional restrictions to the laws of motion, such as:
-- For contact forces, the forces are equal and opposite
/and act at the same point/.
-- For action-at-a-distance forces, the directions of the two
forces are collinear with the line joining the two points of
application.

It's good to discuss these things. This thread has shed light on
several truly fundamental issues.