Air

...It is here but you cannot see it... guess what?...Air
Air is the Earth's atmosphere. Air around us is a mixture of many gases and dust particles. It is the clear gas in which living things live and breathe. It has an indefinite shape and volume. It has no color or smell. It has mass and weight. It is a matter as it has mass and weight. Air creates atmosphere pressure. There is no air in the vacuum and cosmos. Air is a mixture of 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. There is an average of about 1% water vapor. Animals need the oxygen in the air to live. In the human body, the lungs give oxygen to the blood, and give back carbon dioxide to the air. Plants need the carbon dioxide in the air to live. They give off oxygen that humans can breathe again. Wind is moving air. Air can be polluted by some gases (such as ozone and carbon monoxide), smoke, and ash. This pollution is one of the reasons for global warming, by causing the "greenhouse effect".
Other uses of air are as follows:
Aircraft use propellers to move air over a wing, which allows them to fly.
To fill air in balloons, tyres, cushions, inflatable toys
to dry washed clothes
To suck in dust in vacuum cleaner
to blow air
In wind mill
To cool hot objects
To burn fuel
to form bubbles
in piston
This invisible friend is always with me...