The Physics of Spinning
Basketball on Finger
The physics
behind this trick is fairly simple. The main concept is about
understanding centripetal force.
Centripetal Force is a force that acts on a body moving in a
circular path and is directed towards the center which the body
is moving.
Centripetal force is applied to spinning a basketball on a
finger at a particular point.
At that point, the basketball applies one force on the person
spinning it, while we apply two forces on the basketball.
The result is a nonuniform circular motion. Because the point
has a groove (intersection), the ball is more inclined to spin
in a horizontal direction until another force is applied or the
coefficient of drag friction stops the ball and allows it to
fall off your finger.
Another huge concept is that of angular acceleration.
Angular Acceleration is the change in angle over the time^2.
The Force created to keep the basketball spinning is the Angular
Acceleration multiplied by the mass of the basketball.
The final main concept to understand about spinning a basketball
on the tip of your finger is the Law of Angular Momentum which
says momentum must always be conserved.
L= mVr(sin theta)
Law of Angular Momentum says that the velocity of the ball with
respect to the angle and the mass of the ball, that is we
decrease the mass or make the angle tighter, then the object
will spin faster.
IE: Imagine your standing on a disk that has free circular
motion in the horizontal plane, if you held an object with your
arms extended, you will notice a decrease in speed. If you
tucked your arms into your chest or brought the weight as close
to you as possible, your speed will increase.
