Airplane Window by Heute
They both have a tiny hole on their side. Why? Well, pressure, of course.
If you’ve ever taken a window seat on an
airplane you might have noticed that there is a tiny hole at the bottom of the
window glass. Even though it is quite a small hole one can’t help but wonder
what its purpose is. After all, if there is one thing you don’t want to see on
a plane is a hole.
That hole,
however, serves a very important purpose. As you might be aware, airplanes are
pressurized to create a comfortable and safe environment for passengers and crew
at high altitudes where air pressure and oxygen levels are too low for humans
to survive. Otherwise, we would either freeze or pass out from the lack of
oxygen. None of these options are ideal for passengers, let alone for the
pilots and the rest of the crew.
However, the
difference in air pressure between the outside and the inside of the aircraft creates
tension between the glass panes of the aircraft’s windows and if left unchecked
could cause the window to crack or even shatter. I cannot stress this enough,
holes on an airplane are a big no-no.
The easiest
way to fix this would be to not have windows at all. Unfortunately, that would
make for a very unpleasant experience for the passengers and would also create
a safety issue making it harder for passengers, crew, and potential rescuers to
navigate their way in and out of an aircraft in case of a crash. This is where
those tiny holes come in.
Called ‘bleed
holes’ or ‘breather holes’ they are typically located in the middle layer of
the three-layer aircraft window design, and their purpose is to regulate pressure between the
different glass panes and prevent fogging.
This hole
allows the air pressure to equalize between the panes, stopping the outer glass
from bearing the full brunt of the pressure changes as the airplane ascents and
descends during flight, preventing it from shattering. By allowing air to
circulate between the panes it also keeps moisture from accumulating and
compromising visibility.
In case of
an emergency landing, a regular window would most likely shatter due to the
rapid changes in pressure as the plane quickly descends. This tiny hole
prevents that from happening by keeping the window’s structural integrity even
in the most extreme scenarios.
BIC Cristal Pen by Wikimedia Commons
Now that
you have some grasp of why these holes are so important for an aircraft, you
might be wondering why a ballpoint pen would also need one. After all, unless
you are using it during an exam, it’s probably not going to find itself in many
high pressure situations.
Although a
regular ballpoint pen will probably not ever fly to a high altitude, there is
still a difference in air pressure between the inside of the pen and the
outside. The principle is the same as that of an airplane window. The small
hole on its side is there to equalize the air pressure between the inside and
the outside of the pen and to prevent the ink from leakage.
Ballpoint
pens work by applying pressure to the tip of the pen which makes the ball
rotate and the ink to come out through capillary action – the movement of a
liquid within narrow spaces, such as a tube or a straw.
To put it
simple, a liquid in a narrow tube like the one that a pen uses to store its ink
will always be drawn upwards unless there’s a force preventing it.
This way,
by keeping the pressure equalized, the hole on the side of the pen keeps the
ink from leaking while the pen is not being used.
Bad habits die hard
It’s not
just the pen itself that has a hole in it. The pen cap also has a hole on its
top. This however has nothing to do with pressure but it does have to do with
air, particularly with breathing.
Even if you
don’t do it yourself you probably have at least one friend who likes to nibble
on pen caps. You know. The one you never asked to borrow a pen from because
they always looked gross and chewed on.
Because of
your friend and of millions of other people like them, pen caps have a hole at
the top so that if they ever happen to swallow and choke on it, the cap will
not stop them from breathing, by allowing the air to pass through its top.
