52
Mysterious air
pressure
You will need
– Clear plastic cup
– Plastic bowl of water
Here’s how
1. Fill the bowl with water.
2. Dip the cup in it so it fills with water. Then,
turn it over under the water.
3. Now partially pull the cup out of the
water. As long as its opening remains
under the surface of the water, it will not
empty out. As soon as air penetrates, all
of the water in the cup runs out.
Experiment
5
We live at the bottom of a huge ocean of air. The air column above us
weighs heavily on us. We usually don’t feel this so-called
air pressure,
mainly because all of the parts of our bodies are experiencing the
same pressure and we are adapted to it. A vacuum (airless space)
“feels” the full force of the air pressure. Such a vacuum would form if
the water hanging in the cup flowed down under its own weight. But
this is prevented by the external air pressure — it is far greater than
the weight of the water in the cup. It is similar with household suction
cups: Pressing creates a
vacuum
between them and the surface they
are stuck to, so the
air pressure
presses the suction cup firmly against
the surface.
dId YOU KNOW ...
... that a drinking
straw only works
thanks to air
pressure? Sucking
at the top creates
a vacuum in it, and
therefore the air
pressure pushes the
drink into the straw
from below.
W
hAt’s
ha
p
p
eN
in
g
?
