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 so you can hear the very interesting scientific explanation.

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 But the clue is that it must be the sticking, but notall types of tape work.

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 then sometimes scotch tape being pulled can produce X-rays, like enough X-rays 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, Tribo, I learned, comes from the Greek for rubbing or friction, and luminescence, I relearned, is and luminescence, I relearned, is the word for the emission of light in situations not caused the word for the emission of light in situations not caused by heat.

by heat.

For example, you may have heard of bioluminescence, like the recent glowing waves in San Diego which like the recent glowing waves in San Diego which is caused by biological reactions in bacteria.

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 we do understand about triboluminescence and somethings that we don't.

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.

where air violently turns from an insulator into a conductor.

That point is called the dielectric breakdown of air-- 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, Go forth into the world and ask those questions, and happy physicsing.