Question : Why does ice float on water but sink in alcohol?
Answer : Because ice is lighter than water it floats on it. However, ice is heavier than alcohol and therefore it sinks in alcohol.

Question : Why does moisture gather outside a tumbler containing cold water?
Answer : The water vapour in the air condenses on cooling and appears as droplets of water.

Question : Why does kerosene float on water?
Answer : Because the density of kerosene is less than that of water. For the same reason cream rises in milk and floats at the top.

Question : Why is the water in an open pond cool even on a hot summer day?
Answer : As the water evaporates from the open surface of a pond, heat is taken away in the process, leaving the surface cool.

Question : Why is it less difficult to cook rice or potatoes at higher altitudes?
Answer : Atmospheric pressure at higher altitudes is low and boils water below 100°C. The boiling point of water is directly proportional to the pressure on its surface.

Question : Why are winter nights and summer nights warmer during cloudy weather than when the sky is clear?
Answer : Clouds being bad conductors of heat do not permit radiation of heat from land to escape into the sky. As this heat remains in the atmosphere, the cloudy nights are warmer.

Question : Why is a metal tyre heated before it is fixed on wooden wheels?
Answer : On heating, the metal tyre expands by which its circumference also increases. This makes fixing the wheel easier and thereafter cooling down shrinks it; thus fixing the tyre tightly.

Question : Why is it easier to swim in the sea than in a river?
Answer : The density of seawater is higher; hence the upthrust is more than that of river water.

Question : Who will possibly learn swimming faster–a fat person or a thin person?
Answer : The fat person displaces more water which will help him float much more freely compared to a thin person.

Question : Why is a flash of lightning seen before thunder?
Answer : Because light travels faster than sound, it reaches the earth before the sound of thunder.

Question : Why cannot petrol fire be extinguished by water?
Answer : Water, which is heavier than petrol, 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 extinguish the fire. The latter is true if a small quantity of water is poured.