Birds, balloons, and airplanes all need air to fly. Human understanding of air has been a slow process that has spanned many centuries. After all, explaining air is not simple.
Air is invisible.
You cannot easily taste or touch air. Yet air is one of the most important substances on Earth. We now know that air consists of a mixture of gases in which we move, live, breathe, and fly. These elements were the essential substances of which everything else was made. In the days of Aristotle, air was thought to be a uniform substance that occupied all space.