Английский язык в сфере профессиональной коммуникации: природопользование. Тарасова Л.А - 32 стр.

mouths. Air is everywhere and it gives life to every living thing. When
air moves, we call it «wind».
      When we say that a bottle is empty and has nothing in it, that
is not really true, for the bottle is full of air. Push it under water
and you will see the air coming out of it as the water goes in.
      Although we cannot see it, air has some strength. For exam-
ple, it stops a piece of paper from falling as quickly as a piece of
wood. Hold a piece of wood in your left hand and a small piece of
paper in your right hand and drop them together. The wood will fall
quickly, but the paper will fall much more slowly. The two pieces,
dropped together, will fall on the ground at different times. This is
because it was more difficult for the paper to push through the air
than for the piece of wood. But if you put the paper on the piece of
wood and drop them again, they will fall together and reach the
ground at the same time, because the wood pushes the air out of the
way and the paper falls as quickly as the wood does. This shows us
that falling things must push their way through the air.
      This is very useful to airmen. When an accident happens to an
airplane in the air, such as the airplane catching fire, the airman
can jump out and can fall slowly to the earth by his parachute. The
airman held by a parachute does not fall quickly to the ground, he
goes down slowly.
      Airplanes can fly because of the strength of the air. Airplanes
are bigger and heavier than motor cars. How, then, can they keep
up in the air without falling? The answer is this: as the engine pulls
the airplane through the air, the air presses on the under part of the
wings and this holds up the airplane. When an airplane starts from
the ground, first of all it runs on its wheels like a motor car, going
more and more quickly. When the speed is great enough, the pres-
sure of the air under its wings lifts it off the ground and it rises like
a bird.
      Air is a gas. Things called 'solids' keep the same shape when
you put them in a vessel. A piece of wood or a stone do not take the
shape of the vessel. Things called 'liquids' do not keep their shape in
a bottle or a cup. They take the shape of the bottle or the cup, but
they keep their size. Put some water into a bottle or a cup and it will
take the shape of the bottle or a cup. Air is not a solid, for it changes
its shape. And it is not a liquid because it changes its size as well. That
is why we say it is a gas.

32