CONSERVATION OF ANGULAR MOMENTUM
Newton’s second law says that
so if Fnet = 0, then p is constant. This is conservation of linear momentum.
The rotational analog of this is
So if τnet = 0, then L is constant. This is conservation of angular momentum.
Basically, this law says that if the torques on a body balance so that the net torque
is zero, then the body’s angular momentum can’t change.
The Skinny on Spinning
When two objects have
the same mass, the one
that has more of its mass
distributed closer to the
axis of the rotation will be
easier to rotate. Therefore,
when a skater pulls her
arms in, her mass remains
the same but is now closer
to the axis of rotation,
which means that it is
easier for her to spin.The most common example of this phenomenon is when a figure skater spins. As the
skater pulls her arms inward, she moves more of her mass closer to the rotation
axis and decreases her rotational inertia, I. Since the external torque on her is
negligible, her angular momentum must be conserved. Since L = Iω, a decrease in
ω causes an increase in, and she spins faster.