Q:- Why cannot petrol fire be extinguished by water?

Ans:- As water is heavier than petrol therefore slips down permitting the petrol to rise to the surface and continue to burn. Besides, the existing temperature is so high that the water poured on the fire evaporates even before it can extinguisher the fire. The latter is true if small quantity water is poured. Thus the petrol fire can not be extinguished by water.

Q:- Who will possibly learn swimming faster-a fat person or a thin person?

Ans:- Te fat person! The reason is that the fat person displaces more water which will help him float more freely as compared to a thin person.

Q:- Why does water remain cold in an earthen pot?

Ans:- There are pores in an earthen pot which allow water to percolate to the outer surface. Here evaporation of water takes place thereby producing a cooling effect. Therefore the water remain cold in an earthen pot.

Q:- Why it is recommended to sprinkle oil in the ponds with stagnant water to prevent growth of mosquitoes?

Ans:- Mosquitoes breed in stagnant water. The larve of mosquitoes keep floating on the surface of water due to surface tension. However, when oil is sprinkled ,the surface tension is lowered resulting in drowning and death of the larve. Thus it is recommended to sprinkle oil in the ponds with stagnant water to prevent growth of mosquitoes.

Q:- Why does oil rise on a cloth tape of an oil lamp?

Ans:- This is again due to the capillary action. The pores in the cloth tape suck oil due to the capillary action of oil. Thus oil rise on a cloth tape of an oil lamp.

Q:- Why are ventilators in a room always made near the roof?

Ans:- The hot air is lighter in  weight tends to rise above and escape from the ventilators at the  top. This allows the cool air to come in the room to take its place. Therefore the cool air makes the room cool. Thus the ventilators in a room always made near the roof.