Question : Why do we lean forward while climbing a hill?
Answer : In order to keep the vertical line passing through our center of gravity always between our feet, which is essential to attain equilibrium or stability.

Question : Ice wrapped in a blanket or sawdust does not melt quickly. Why?
Answer : Both wood and wool are bad conductors of heat. They do not permit heat rays to reach the ice easily.

Question : Why does a thermometer kept in boiling water show no change in reading after 100°C?
Answer : The boiling point of water is 100°C. Once the water starts boiling at this temperature, thermometer records no change in temperature. The quantity of heat supplied is being utilised as latent heat of evaporation to convert the water at boiling point into vapor.

Question : Why do we bring our hands close to the mouth while shouting across to someone far away?
Answer : By keeping hands close to mouth the sound is not allowed to spread (the phenomenon of diffraction of sound) in all directions but is directed to a particular direction and becomes louder.

Question : Why does a corked bottle filled with water burst if left out on a frosty night?
Answer : Because of the low temperature the water inside the bottle freezes. On freezing it expands, thereby its volume increases and pressure is exerted on the walls.

Question : Why is a small gap left at the joint between two rails?
Answer : To permit expansion of rails due to the heat generated by the friction of a moving train.

Question : Why cannot a copper wire be used to make elements in the electric heater?
Answer : Copper melts at I08.3°C and forms a black powder on reacting with atmospheric oxygen. For heater elements, a metal should have more resistance to produce heat.

Question : Why are water or mercury droplets always round .when dropped on a clean glass?
Answer : The surface of a liquid is the seat of a special force as a result of which molecules on the surface are bound together to form something like a stretched membrane. They tend to compress the molecules below to the smallest possible volume which causes the drop to take a round shape as for a given mass the sphere has minimum volume.

Question : Why does a balloon filled with hydrogen rise in the air?
Answer : Weight of hydrogen is less than the weight of air displaced by it. In balloons, hydrogen is normally filled because it is lighter than air.

Question : Why does smoke curl up in the air?
Answer : Smoke contains hot gases which is lighter in weight, follow a curved path because of the eddy currents that are set up in the air.

Question : Why does an electric bulb explode when it is broken?
Answer : The bulb encompasses partial vacuum and as it breaks, air rushes in causing a small explosion.