DIANNA: Thanks to CuriosityStream for supporting
PBS Digital Studios.
You start to question your sanity after you've
opened hundreds of Band-Aid wrappers alone in your closet
but you haven't put any of them on yet.
Hey, I'm Dianna.
You're watching "Physics Girl".
And the reason that I've been opening hundreds of Band-Aid
wrappers, besides the fact that I'm trying to start a trend,
is because when you open them in the dark--
I know, I wouldn't have thought to try that either-- they
produce this blue glow.
I'm going to show you the footage in a second.
Honestly, it's kind of hard to see on camera.
So I would suggest just going into a closet and trying it
yourself.
Let your eyes adjust to the dark for a bit
while you keep this video playing
so you can hear the very interesting
scientific explanation.
Not even saying that for the sweet, sweet watch time.
Yes I am.
OK, here's the footage of the Band-Aid glowing
at regular speed.
Check out that glow.
I never knew in all those years of opening Band-Aids.
And you notice that it doesn't work as well for some
Band-Aids, like certain brands work better than others--
clue number one as to what's going on.
But then I also filmed it in high speed.
So here's the footage at a quarter of the speed.
Unfortunately more grainy because I
had to turn up the ISO to pick up enough light
to be able to film it at such a high frame rate.
Yup, it's definitely glowing.
Why-- my favorite question-- do these Band-Aids
produce that glow?
One clue as to what's going on is that it's the ripping open.
It's the motion or the unsticking that
causes the light to happen.
Then here's another clue.
You might have eventually tried this on your own,
but this also works with some types of tape.
I tried Scotch tape, duct tape, packing tape.
But the clue is that it must be the sticking, but not
all types of tape work.
And the very last important clue is
that if you try this in a different gas other than air,
like neon, then the glow is a different color.
What?
And then if you try it in air but you
suck out a bunch of the air and produce a moderate vacuum,
then sometimes scotch tape being pulled
can produce X-rays, like enough X-rays
to show the bones in your finger.
Come on.
I love that the scientists in that experiment
thought to X-ray their finger with their experiment.
Scientists are great.
OK, now comes the hard part, trying
to put all the clues together and also
a bunch of scientific articles listed in the description
and figure out what's going on.
Listen, I've got a little bone to pick with other YouTube
videos that claim that this effect is not well understood.
It's like they got to this line in their favorite source
and were like, OK, that's good enough for me.
So we're going to get to the heart of what's going on.
Don't worry, if it hurts, I've got Band-Aid.
Motion is important for the light production.
There is a word for an effect where
the relative motion of two surfaces creates light,
and it's called triboluminescence.
I'm doing the thing that I hate, just naming jargon,
but it is a pretty sweet word.
Tribo, I learned, comes from the Greek for rubbing or friction,
and luminescence, I relearned, is
the word for the emission of light in situations not caused
by heat.
For example, you may have heard of bioluminescence,
like the recent glowing waves in San Diego which
is caused by biological reactions in bacteria.
And evanescence is also the emission of light.
[MUSIC - EVANESCENCE, "BRING ME TO LIFE"]
AMY LEE: (SINGING) Save me from the dark.
That's-- that's a joke.
Sometimes you've got to clarify on scientific videos.
Spoiler alert, we're pretty confident that this
is triboluminescence.
But what causes triboluminescence?
Now I want to make it clear here--
[CLEARS THROAT],, Wikipedia-- that there are some things that
we do understand about triboluminescence and some
things that we don't.
We do know that triboluminescence
is caused by the build up of excess charge
or charged particles that lead to a spark.
It's kind of like the process that
produces lightning or an electrostatic
spark like when you shock yourself on a metal door knob.
It goes something like this.
You create a separation of charges,
say positive charges over here, negative charges over there.
And the positive and negative charges are like, I miss you.
I need to be with you.
But the electrons typically can't jump through air
to the positive charges because air is typically
an electrical insulator.
But if you build up enough charge,
you get a super strong pull, and you can reach the point
where air violently turns from an insulator into a conductor.
That point is called the dielectric breakdown of air--
more jargon.
When that happens and the electrons
start to flow through the air, electrons
are stripped off of air molecules left and right.
Or, in other words, the air molecules become ionized,
and then light is produced in that moment when electrons
jump to the ionized molecules.
This ionization part would explain
why the glow is a different color in different gases
because ionization of different molecules or atoms
produces different light spectra.
That's how we get the colors in neon lights, which
ironically and importantly are not all made of neon.
Now, what we don't know is the exact mechanism
for how charges get separated.
We think we understand pretty well the triboelectric effect,
which is that when you rub materials together
like a balloon and your hair, charges build up
because some materials hold on to their electrons
more than others.
They have different electron affinities,
a good term to remember if you want to look up more
about this later.
That's why the glow didn't work as well with different bandage
brands and different types of tape
because they're made of different materials.
But triboelectricity also depends on the humidity
and how you rip open the Band-Aid,
and it depends on the type of motion,
whether it's unsticking or relative motion like friction.
And the energy that holds the tape together
is the van der Waals interaction,
which is a hundred times smaller than the energy needed
to produce a visible light photon.
So how do we get visible light, and how
are the X-rays made in this situation with the vacuum?
There are hypotheses for that as well.
I'll link to some of the sources in the description.
It's still being explored.
And, I know some of you are waiting for this question.
You can get a similar effect to the Band-Aid glow by smashing
candy.
Something different must be going on there.
The hypothesis goes that the separation of charges
in that situation is crystal structures breaking rather
than rubbing of materials.
Dude, there are still a lot of unanswered questions
for scientists in the lab and for us
here in our boredom palaces.
That's where the learning happens.
You don't necessarily notice the coolest phenomena
unless you take objects out of their normal environment.
And the seemingly most simple phenomena
don't always have the simplest explanation.
That is all I have for you today,
except maybe I should take a quick moment
to address the seven-digit elephant in the room.
I can't freaking believe we crossed a million subscribers.
You guys, when I started this channel
I stood on my diploma trying to reach a higher
shelf because I didn't know what to do with a physics degree.
This is not what I thought I would end up doing with it.
I mean, it still may not be what I end up doing with it,
but this has been the journey of a lifetime.
My gosh, I've had so much, so, so, so much fun.
You guys ask me the craziest questions.
You send me the craziest comments.
I feel like reaching a million subscribers needs
a little bit more than my unthought-through word vomit
right now.
But I'm just so thankful, so excited.
Thank you for four, five, sixish years-- who even knows?
We're going to do something to celebrate.
We'll do something.
But in the meantime, go forth into the world
and ask those questions, and happy physicsing.
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