1. Why are Man holes on the drainages are and should be circular in shape?
In square shaped man holes, the lid would easily enter the hole diagonally, but it is not possible in circular man holes.

2. Why is the sky blue?
(Scattering of light) Violet and blue light have short waves which are scattered more than red light waves. While red light goes almost straight through the atmosphere, blue and violet light are scattered by particles in the atmosphere. Thus, we see a blue sky.

3. A man with a load jumps from a high building. What will be the load experienced by him?
Zero, because while falling, both the man and the load are falling at the same acceleration i.e. acceleration due to gravity.

4. A piece of chalk when immersed in water emits bubbles. Why?
Chalk consists of pores forming capillaries. When it is immersed in water, the water begins to rise in the capillaries and air present there is expelled in the form of bubbles.

5. Why does a liquid remain hot or cold for a long time inside a thermos flask?
The presence of air, a poor conductor of heat, between the double glass wall of a thermos flask, keeps the liquid hot or cold inside a flask for a long time.

6.Why does a ball bounce upon falling?
When a ball falls, it is temporarily deformed. Because of elasticity, the ball tends to regain its original shape for which it presses the ground and bounces up (Newton's third law of motion)

7. Why is standing in boats or double decker buses not allowed, particularly in the upper deck of buses?
On tilting the centre of gravity of the boat or bus is lowered and it is likely to overturn.