Purpose: Conservation of Angular Momentum.
Keep the platform on the floor, let a volunteer stand on it(feet should spread out and align the body so that the center of mass is right over the center of mass of the platform).
Give two equal weights to his hands. Ask him to hold each weight far away from the body so that his hands are vertical. Give him a spin not too fast not too low. Ask him to bring his arms closer to body as fast and uniformly as possible. Watch out the speed change. This explains the conservation of angular momentum, as inertia changes velocity changes to keep momentum conserved (L=I?).
This also can be used along with the spinning bicycle wheel.
Instead of weights, now hand over the spinning bicycle wheel to the person on the platform, Have him hold it so that two handles are horizontal. Ask him to slowly turn the wheel either side and note the direction and speed of rotation of the platform.
Note: Leave plenty of space around the platform, just in case if the person on the platform need to step off quickly.