Materials required: - 2 onions and 2 broomsticks.

Arrange the two sticks as shown in the picture. Rest one end of the long stick on your finger horizontally and see how wonderfully it balances. Tilting it this way or that way does not lose its balance. The attachment of the second onion to the top one makes the centre of gravity of the top stick fall outside its point on the left and hence it is balanced with stable equilibrium. Many toys like rocking doll, rock horse, etc. are made based on this principle.

Materials required: - 3 onions and 3 broomsticks. Take 3 broomsticks (one long and two short). Insert the long broomstick into an onion so that it is at 1/3rd distance from the bottom. Insert two short broomsticks at the side of the onion to form an angle. Insert one onion each at the end of two small sticks as shown in the figure. Place the bo­ttom of the long stick on your finger and let it balance. Tilt it. Even then it would not fall down; but it oscillates wonderfully.

How does it balance?
Centre of gravity is at the middle of the stick. It is far above the bottom point of the stick. Without the onion the stick does not balance vertically on your finger. But when the two onions are attached to the sides, the centre of gravity is lowered down even below the stick point. Now, the end rests on the finger in a stable equilibrium. So even if you tilt in any way the stick rests comfortably on the finger.

Materials required: - a small stone, a big stone, two square cards, a feather and a small tin lid. Take both the small and big stones. Drop both the stones from above. Watch them carefully. Which stone will touch the ground first? Is it the big stone or the small stone? Why? Repeat the same either from the ladder or top floor of a building.
Now place the feather on the tin lid and drop it. Which will touch the floor first? Tin or feather or both. Keep two cards one above the other and drop them. Which card will reach the floor first? Why? The earth pulls the small and big stones in the same way. Weight is not the criterion here. Therefore, both the stones dropped together. Similarly in the second experiment, both the tin lid and feather reached the ground at the same time. In the third experiment also, the cards together reached the floor. These are all due to the gravitational force of the earth. Sir Isaac Newton discovered it. The great Italian Scientist, Galileo demonstrated it.