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):

1. When pressure is carried out to the blades of the primary, the firki shows rotation.
2. The pressure is carried out to the blades of the primary through transferring air referred to as wind, however, as there's no air movement (wind) in a closed area, firki no longer rotates.

Observation (b):

1. The arrow of weathercock factors in a selected course as it shows the modern course of the wind (air) at that time.

Observation (c) :

1. We can say that an empty glass isn't genuinely empty as it is filled with air.
2. We cannot see the air, however, we will experience it as it's obvious and weightless.
3. Air now no longer has a set form or volume.

Observation (d):

1. It is accurate to say that respiration via mouth can be dangerous due to the fact that the air contains dirt debris, and if we breathe through the mouth, the damaging dirt debris may also enter our bodies (breathing system) and cause lung damage.
2. However, if we breathe through our nostrils, the first-class hair and mucus in our nostrils may also save us from doing so.