Q:- Why does a ball bounce up upon falling?

Ans:- According to the Newton’s third law, to every action there is equal and opposite reaction.

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 (due to the Newton’s Third Law of motion)

Q:- Why do we perspire on a hot day?

Ans- Do you know that we have sweat glands in our body.

When the body temperature increases on a hot day then the sweat glands are stimulated to secrete perspiration. It is the nature’s way to keep the body cool. During the process of evaporation of sweat, body heat is taken away, thus, giving a sense of coolness.

Q:- Why do we perspire before rains?

Ans:- Sometimes before the rain falls, the atmosphere has lots of moisture or in other words atmosphere gets saturated with water vapor, therefore , the process of evaporation of sweat is delayed. Thus sometimes we perspire before rain.

Q:- Why does a thermometer kept in boiling water show no change in regarding after 100^o C?

Ans;- Do you know that the boiling point of water is 100^oC. Once water starts boiling at this temperature, thermometer records no change in temperature. The quantity of heat supplied is being utilized as latent heat of evaporation to convert the water at boiling point into vapor.

Q:- Why do we bring our hands close to the mouth while shouting across to someone far away?

Ans:- Do you know the phenomenon of diffraction? Diffraction is the bending of the light at the corners of an obstacle.

By keeping hands close to mouth the sound is not allowed to spread (phenomenon of diffraction of sound) in all directions but is directed to a particular direction and therefore the sound becomes louder.