Question : Why do we perspire before rains?
Answer : Before the rain falls, the atmosphere gets saturated with water vapour, as a result, the process of evaporation of sweat is delayed.

Question : Curved rail tracks or curved roads are banked or raised on one side. Why?
Answer : Because a fast moving train or vehicle leans inwards while taking turn and the banked or raised track provides required centripetal force to enable it to move round the curve.

Question : How do bats fly in dark?
Answer : When bats fly they produce ultrasonic sound waves which are reflected back to them from the obstacles in their way and hence they can fly without difficulty.

Question : Water pipes often burst at hill stations on cold frosty nights. Why?
Answer : The temperature may fall below 0³C during cold frosty nights which converts the water inside the pipes into ice, resulting in an increase in volume. This exerts great force on the pipes and as a result, they burst.

Question : Why are ‘white clothes more comfortable in summer than dark or black ones?
Answer : White clothes are good reflectors and bad absorbers of heat, whereas dark or black clothes are good absorbers of heat. Therefore, white clothes are more comfortable because they do not absorb heat from the sun rays.

Question : Why is rose red and grass green in daylight?
Answer : Rose absorbs all the constituent colours of white light except red which is reflected us. Similarly, grass absorbs all colours except green which is reflected us.

Question : Why does a ship rise as it enters the sea from a river?
Answer : The density of sea water is high due to impurities and salts compared to river water. As a result, the upthrust produced by the sea water on the ship is more than that of river water.

Question : Why are fuses provided in electric installations?
Answer : A safety fuse is made of a wire of metal having a very low melting point. When excess current flows in, the wire gets heated, melts and breaks the circuit. By breaking the circuit it saves electric equipment or installations from damage by excessive flow of current.

Question : Why is it easier to lift a heavy object under water than in air?
Answer : Because when a body is immersed in water, it experiences an upward thrust (Archimedes’ Principle) and loses weight equal to the weight of the water displaced by its immersed portion, and hence, is easier to lift objects.

Question : If a highly pumped up bicycle tyre is left in the hot sunlight, it bursts. Why?
Answer : The air inside the tube increases in volume when heated up. As sufficient space for the expansion of the air is not available because the tube is already highly pumped, it may result in bursting of the tyre.

Question : What will be the colour of green grass in blue light?
Answer : Grass will appear dark in colour because it absorbs all other colours of the light except its own green colour. The blue light falling on grass will be absorbed by it, and hence, it will appear dark in colour.