Q:- Why is it less difficult to cook rice or potatoes at higher altitudes?
Ans:- Atmospheric pressure at higher altitudes is low and boils water below 1000 C because the boiling point of water is directly proportional to the pressure on its surface. As less boiling point is required at higher altitudes therefore it is less difficult to cook rice or potatoes at higher altitudes.
Q:- Why is the water in an open pond cool even on a hot summer day?
Ans:- This is due to evaporation. As the water evaporates from the open surface of a pond, heat is taken away in the process, leaving the surface cool.
Q:- Why is it difficult to breath at higher altitudes?
Ans:- Because of low air pressure at higher altitudes the quantity of air is less, and if air is less so also that of oxygen. Therefore it is difficult to breath at higher altitudes.
Q:- Why are winter nights warmer and summer nights hotter during cloudy weather than when the sky is clear?
Ans:- Clouds are bad conductors of heat and therefore do not permit radiation of heat from land to escape in to the sky. As this heat remains in the atmosphere, thus the cloudy nights are warmer.
Q:-Why is metal tyre heated before it is fixed on wooden wheels?
Ans:- You must know that on heating metal expands and on cooling it shrinks. Therefore 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.
Q:- Why is it easier to swim in the sea than in a river?
Ans:- The density of sea water is higher, hence the upthurst is more than that of river water. Thus it is easier to swim in the sea than in a river.