The spinning that we have all seen done
by a figure skater once in our lives is done to perfection by the conservation
of Angular Momentum.
Before going into the
relationship between the figure skater’s spin and angular momentum here is some
information that needs to be taken into consideration:
Angular momentum= moment of inertia x angular speed
Moment of inertia is dependent upon the mass distribution and
the location of the axis of rotation.
I=MR2
Angular Speed is the velocity of something divided by its radius
So to go
on to show the relevance of angular momentum to a skater’s spin. When a skater’s angular speed increases this
means that he/she pulls her arms and legs as close to the center of the body as
possible. In order to slow the spin down
the skater stretches he/she’s limbs out away from the trunk. However, this is opposite for the moment of
inertia, when the arms and feet are brought towards the body the moment of
inertia decreases and it increases when the limbs are extended
If torque
is considered which is:
Change in
angular momentum/time interval
One must
realize that the torque will be greater if the moment of inertia increases. The
force to rotate an object about some axis is known as the measurement of
torque:
Torque=Force x (d) lever arm of the force
To see a
problem solved using this theory go to the website:
http://www.bsharp.org/physics/stuff/skater.html