Explain the following observations very briefly
(a) A firki does not rotate in a closed area.
(b) An empty glass in fact is not empty.
(c) Breathing through mouth may harm you.

Explanation

(a) Lack of air movement. (b) Shows the latest direction of the wind. (c) Even the so called empty glass is not in fact empty. It is filled with air. (d) You may inhale dust if present in air which may prove harmful.