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Summary:
 Does the motion ever "stop"
Basic zero clearance frictionless model of a crank journal turning with an attached bar on that journal.
Bar moves up and down in Sine fashion, components of journal Velocity vector change accordingly (showing clockwise rotation here), and Velocity of the attached bar only has a Y component (up and down).
All simple thus far.
Now, here's the tricky question, does the bar ever stop moving? We know the Velocity of the bar has to pass through zero at Ymax as the bar itself changes direction, but there is no dt where dx=0, or in other terms, for any dt the dx !=0 .
So from a physics perspective, when V=0 does this attribute alone define motion? The acceleration vector is not zero when V=0, so doesn't this tell us the body is still in motion? Surely we can select a finite point in time to see where V=0, but can a point in time define motion, or must dt/dx be the thing that defines motion?
Bar moves up and down in Sine fashion, components of journal Velocity vector change accordingly (showing clockwise rotation here), and Velocity of the attached bar only has a Y component (up and down).
All simple thus far.
Now, here's the tricky question, does the bar ever stop moving? We know the Velocity of the bar has to pass through zero at Ymax as the bar itself changes direction, but there is no dt where dx=0, or in other terms, for any dt the dx !=0 .
So from a physics perspective, when V=0 does this attribute alone define motion? The acceleration vector is not zero when V=0, so doesn't this tell us the body is still in motion? Surely we can select a finite point in time to see where V=0, but can a point in time define motion, or must dt/dx be the thing that defines motion?
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