Question : Why does ice float on water?
Answer : The weight of the ice block is equal to the weight of the liquid displaced by the immersed portion of the ice.
Question : A man with a load jumps from a high building. What will be the load experienced by him?
Answer : Zero, because the acceleration of his fall is equal to the acceleration due to the gravity of the earth.
Question : A piece of chalk when immersed in water, emits bubbles. Why?
Answer : 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.
Question : Why does a liquid remain hot or cold for a long time inside a thermos flask?
Answer : 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.
Question : Why does a ball bounce upon falling?
Answer : 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).
Question : Why is standing in boats or double decker buses not allowed, particularly in the upper deck of buses?
Answer : On tilting the center of gravity of the boat or bus is lowered and it is likely to overturn.
Question : Why is it recommended to add salt to water while boiling dal?
Answer : By addition of salt the boiling point of water gets raised which helps in cooking.
Question : Why is the boiling point of sea water more than that of pure water?
Answer : Sea water contains salt, and other impurities with different boiling points, which jointly raise its boiling point.
Question : Why is it easier to spray water to which soap is added?
Answer : Addition of soap decreases the surface tension of water. The energy for spraying is directly proportional to surface tension.
Question : Which is more elastic, rubber or steel?
Answer : Steel is more elastic for the same stress produced compared with rubber.
Question : Why is the sky blue?
Answer : 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.