But now I can calculate (and plot) the total angular momentum of this ball-spring system. Actually, I can't plot the angular momentum since that's a vector.

The angular momentum of a spinning object will remain the same unless an outside torque acts on it. In physics when something stays the same we say it is conserved . That's where the phrase ...

All this wizardry depends on another form of momentum: the ball’s spin, or more formally, angular momentum. “Watch the really, really, really good [players],” says Goodwin.

Summer Fun: How to transfer momentum from a basketball to a tennis ball Dave Maiullo, Physics Support Specialist at Rutgers University, does a very simple demonstration using just a tennis ball ...