On 12/29/2016 12:46 PM, Vibrator ! wrote:
What's wrong with the centripetal tether example?
With the engine turned off (no thrust) putting the tether in place doesn't change the angular momentum at all. The cross product of the linear momentum of the object with its radius vector remains unchanged. Since it's exerting no torque on the pivot, that must be true, classically.
Meanwhile, the linear momentum of the tethered object is changing constantly, as its velocity vector rotates. But it's also exerting a force on the pivot point, as a result of which the linear momentum of whatever the pivot is anchored to is also changing constantly, in such a way that the sum of the two remains constant. (Energy, not so much, as it goes as the square of the velocity and hence has zero derivative WRT velocity at zero velocity.)
There's no interconversion between linear and angular momentum. As I already said, they're conserved separately.
