Explain the following observations very briefly.
(a) A firki does not rotate in a closed area.
(b) The arrow of weathercock points towards a particular direction at a particular moment.
(c) An empty glass, in fact, is not empty.
(d) Breathing through the mouth may harm you.
Explanation of observations:
Observation (a):
Observation (b):
Observation (c) :
Observation (d):