You must have noticed a question mark shape in the kit, and perhaps puzzled with the kind of toy it is. Let us play with it. The question mark has a circular head and a long tail. Just try and see if it stands on your fingertip if you keep end of the long side of question mark on your finger? Can it stand? Of course, it cannot. The moment you remove your thumb, holding the question mark, away from it, it falls down. Needless to say that the whole body of a question mark cannot rest on just one end of it. Can you ever do it? Even if we allow; you to use any other thing along with this piece, can you make it stand on a fingertip? There is a trick to do it. See the question mark carefully. You will find a slot on the circular side of the question mark.
Insert a leather belt which boys often wear in this slot and try to balance it on your fingertip again.
Wow, it just happens! The question mark stands on your fingertip quite easily.
How does it happen?
We are all aware that earth's gravity acts on us and we are attracted towards the earth because of this gravitational pull. We can stand on the ground on our feet. Similarly, we can lie flat or even sit on the; ground. In all these postures, center of gravity of our body is well within the base of our body, giving it necessary stability. We may not be able to stand on single arm even if we attempt it. When we stand on one leg, we often lean on one side a little bit so that the centre of gravity passes through our standing leg. Now look at the Question Mark again. You can rest it on table comfortably on its flat surface. At the most, you may be able to keep it standing on its edge. However,it is impossible to make it stand on its one end. When we add belt to the question mark, overall scenario changes. If you look carefully, the slot in which the belt is inserted has a specific angle. As the belt is inserted, it is automatically tilted inside. Now we have to consider centre of gravity of not just the question mark, but belt and question mark together. As the belt is tilted inside, the C.G. also gets shifted inside. That means, it comes at the end of the question mark. This makes the question mark stand easily on its end. See if you can use any other object in place of a belt? What is Centre of Gravity? C.G. of a body is a fixed point through which the resultant force of gravity always passes, irrespective of the position of the body.