BALANCING MAGIC HOOK
The Balancing Magic Hook allows for its center of gravity to be manipulated by the addition of weight to the hooked end. Once you know the secret, you can easily balance it on the tip of your finger… or on the end of a pencil… or even on the tip of your nose!
Balancing toys were popular in the 19th century. Dating back to ancient China and India, where they were most often carved from soft wood, the western balancing toys were traditionally made from tin or metal. Illustrations of balancing toys can be found in educational literature from the 18th century. The physics governing the movement of such toys intrigued and amazed people
Figure 1 shows a balancing magic hook in (full-size) cross-section, and can be used as a pattern from which to make your own balancing magic hook. It can be made from a variety of materials: wood, metal, thick cardboard, etc. The ideal thickness is about 1 cm (the aluminum one I have is 9 mm thick).
Once the balancing magic hook has been made, position it on the end of a fingertip as shown in Figure. 2. It is unstable in this position and falls to the floor. Now take a belt (preferably a firm leather one with a reasonably large buckle), and fasten the buckle so that the belt forms a closed loop. Place the belt on the hook (on your fingertip) as shown in Fig. 3, with the buckle at the bottom of the belt.
Instead of the balancing magic hook and belt falling to the floor, the entire system is quite stable! For added effect you can swing the hook and belt gently from side to side, or place it on the edge of a table or the top of a door frame. Figure 3 The hook is unstable by itself, but stable when the belt is hung on it.
HOW IT WORKS — If an object (which is free to rotate) is to be in stable equilibrium, the centre of mass must be below the pivot point. When the hook alone is placed on a fingertip, it is impossible for the centre of mass to be position below the pivot point without the hook sliding from the finger and falling. (The pivot point is just the contact point between the hook and the finger.) When the belt is on the hook, the centre of mass of the system (hook + belt) is now positioned somewhere in the middle of the loop formed by the belt, and it is “easy” for the centre of mass to be under the pivot point, with stable equilibrium being the result.