Kind: captions
Language: en
if there were a portal through which you
could see all of the invisible air
currents temperature gradients and
differences in pressure and composition
of
air then this is what it would look like
to strike a
match
this is helium being squeezed out of a
balloon
you could see the warm air Rising off
your
hands the invisible Vapors of isopropyl
alcohol and the plume of ejected
material when you
sneeze
this is the setup for how I made those
shots over here I have a 40 cm diameter
concave parabolic mirror normally this
would be used to make a telescope but if
it Formed just a tiny piece of a big
spherical shell right a giant spherical
mirror that we're inside then the center
of that mirror would be right here and
that's where I've placed this led it's
3mm but I tried to make the light source
even smaller by painting it with some
black nail nail polish so we try to
approximate a point source of light
there now that light spreads out in all
directions and it bounces off the mirror
and reflects back almost to exactly the
point where the light is you can see
that the light converges to a point
right there now I've offset the light
just a little bit so that this light
will pass straight through and into the
lens of my camera so right here I
position this razor blade so it cuts off
about half the light passing through
this setup allows you to see Tiny
variations in what is in front of the
mirror for example when you have hot
gases coming off of a candle well you
can see that because as the reflected
light from the LED passes through this
column of hot air it changes directions
ever so slightly that is it refracts and
the reason for that is because the
refractive index of hot air is different
from the refractive index of the cooler
air around it now refractive index is a
measure of how fast light travels
through a medium relative to its speed
in a vacuum so for air the value is
pretty close to one but hotter air
actually has a lower index of refraction
in this case the difference in
refractive index is incredibly tiny and
so we don't notice the deflection of the
light but with this setup it actually
makes a difference because some of the
light that would have passed over this
razor blade instead gets deflected down
and gets blocked and that forms a darker
spot on the image similarly some light
that would have hit the razor blade is
instead deflected over it creating a
brighter spot on the image and that is
how this works so you can see the heat
rising off your
head and you can see your
breath and you can see the cold air
poured out of a cup of
ice but temperature is not the only
thing that affects the refractive index
different materials different substances
they have different ref ractive indices
for example the butane in a lighter
obviously we can't see that it's coming
out right now but the camera can even
before the lighter is
lit light also refracts when it passes
through a bubble and the amount depends
on the thickness of that bubble
film this technique is known as schin
based on the German word Scher which
means streak and it was first observed
in 1665 by Robert Hook who was using two
candles and some lenses then in the 19th
century they used this method to try to
find defects in the glass used to make
lenses and more recently people have
used schen to study aerodynamics and
fluid flow because it allows you to see
those pressure differences and
temperature gradients so you can look at
shock waves and differences in the
composition of gases so when you watch
the lighting of this match you're seeing
heat generated from friction igniting
phosphorus which in turn generates more
heat and Begins the reaction between
sulfur and potassium chlorate which
releases sulfur dioxide which you can
also
see and you can see my breath as I blow
out the
flame
I am so excited that I got this set up
to work so if you can think of anything
that would look really cool and schen
then let me know in the comments and I
will try to make it happen and if you're
new to this channel will click here to
subscribe I've got some awesome videos
coming up very
soon