Mass On String - Orbits With Varying Radius
To illustrate conservation of angular momentum.
Ball of string and metal tube.
Rotate the mass on the string with the central end of the string passing through the tubular metal collar.Pulling the string decreases the radius of the ball, thus decreasing the moment of inertia and increasing the angular speed of the ball.
John H. Walters, Jr., Centripetal Force Apparatus, AJP 29, 212, (1961).