To demonstrate the phenomenon of rotational inertia using a circus trick.
1. A two or three feet long stick or ruler.
2. Some clay.
1. Take the stick and attach the clay as a lump near one end.
2. Try to balance the stick on your index finger at the end which is nearer to the lump of clay.
3. Next, try to balance the stick on your finger at the other end that is the end farthest from the lump of clay. Observe at which end it was easier to balance. You will find it easier to balance when the clay is at the top end and not near your finger.
An object has more inertia when its mass is more. In this case the end of the stick with the lump of clay has more mass and hence more inertia. When the heavy end is at the top, the inertia of the mass tries to hold it where it is and resists the gravitational pull which pulls it sideways for an instant. Hence you get time to adjust your finger accordingly in this time and keep it balanced.