This video is sponsored by CNRS Editions.
My question is this: is it or is it not a myth
that people regularly slip on banana peels and fall?
Has anyone in France already fallen
because they stepped on a banana peel?
It drives me crazy.
Let's go.
So you often ask me how I find my video ideas.
Sometimes they come from watching one of Squeezie's videos.
And you know what, I am with him on this.
Because bananas are famously very slippery.
But I'm more worried about winter in Montreal than a banana peel
on the ground.
So that's what we're gonna do today, we will put it to the test and see if,
even though it doesn't seem very slippery now, if in reality,
it is very slippery.
And so we're going to do a slide test.
That's not the officially term at all, obviously.
But I think it's funny.
Is a banana peel more slippery than my shoe?
My god, come on!
This slanted board test is used to determine
the coefficient of friction of a couple of objects.
Here, the banana and the plank.
And this coefficient of friction will really vary depending on the materials we have.
If I had a board made of rubber or ice
or I don't know what,
we would not have the same coefficient of friction with the banana.
So it's very very sensitive to the materials involved.
So here, we're specifically testing
the coefficient of friction of the banana peel with this board.
And what we saw with the test from before is that, in fact, my shoe
begins to slide on the board long before the banana does.
So that means that technically, my shoe is more slippery
than the banana.
It's a bad start for the notion of a slippery banana.
The advantage is that you can measure quite accurately
what is the coefficient of friction,
of the banana-plank couple, because there is a formula for that which is:
slipperiness = tangent theta.
And tetha is the angle between the board and the table.
So in order to find the slipperiness of my banana with this board,
I just have to measure the angle.
Okay that's good.
Testing the board.
The angle we need to look at is the one that will change
as I raise my board.
Okay, 52.
So we find that theta was
52 degrees, which gives us a coefficient of friction of 1.3.
That's huge.
Huge.
To compare,
let's see what we get with a shoe: 0.7.
And if I refer to a paper
which gathers some coefficients of friction, in this paper,
it is indicated that leather on wood has a coefficient of friction of 0.35
and fabric on fabric has a coefficient of friction of 0.3.
So the banana that we found at a 1.3 coefficient of friction, that's huge.
The reason it is interesting to know the coefficient of friction of a banana
is because that allows us to know how
we should walk if we wanted to cross a banana field.
Let me explain, I'll take my shoe back.
When we walk, we first plant our heel down and then roll the foot.
If you plant your heel at a big angle like this,
you have a much higher chance of slipping.
It's like taking a huge step.
You'd be very likely to slip whereas if you plant your heel
at a very small angle here, you will slip a lot less.
It's as if you would walk tiny little steps like this.
What the experiment with the board tells us is that ultimately,
the angle of attack of our foot can be 52 degrees
in order to walk safely in a field full of bananas.
So the story of the slippery banana, since we can go up to a
52 degree angle before starting to slip... meh.
Yes but no, it's a little more subtle than that. This doesn't account for
what goes on as we step on the banana.
And this is where everything changes.
And for this I'll refer to two articles which were published by the same author
and which won him an Ig-Nobel award.
You know, the research award for
slightly quirky research, shall we say.
And this article shows that really, the behavior
between the slant board test, which is a fairly standard test,
is very different from when we walk, when you put weight on the banana.
In fact, when we step on the banana peel, under our weight,
it will generate mucus which will lubricate the banana.
Between the peel and the ground.
At least that's what the article says.
We'll try to see it under the microscope.
So if I apply pressure, are we going
to see mucus coming out...?
We see that it changes color,
it goes from yellow to white to brown.
And it gets a lot more moist.
So it was already a little moist
on one side here, but here it's now very very very moist.
You can see here
I'm getting some sort of banana slime.
So what that means is that if the behavior of the banana changes
when we step on it,
that means that the board test is no good.
This just can't work on the board.
And by the way, this is what they did in the Ignobel paper,
they tried the board experiment but it didn't work.
So they moved on to another test where they used
equipment that I obviously don't have in my little home studio.
And the result they got with their equipment was
another coefficient of friction, far from the 1.3 we had found.
They found 0.066.
It is extremely low.
And for comparison's sake, a pair of skis on snow
have a coefficient of friction around the same figure, below 0.05.
So when you step on a banana peel,
when you put some weight on it,
it gets as slippery as skiing on the snow.
But I want to go a little further here because this phenomenon of lubrication
is super interesting.
And this actually brings together two of my favorite subjects: mechanics and the skeleton.
Mechanics. Skeleton.
So with the mucus,
we have a phenomenon of lubrication, it is the hydrodynamic friction.
I love this, there is a category called creamy friction (in French),
but that's not the one we're looking at today.
So there is a category called hydrodynamic friction,
which is when there's no more contact between surfaces.
There is no more contact because,
between the banana and the plank, it is the mucus that occupies the space.
And this mucus actually creates a banana-based aquaplaning phenomenon.
So when you slip on a banana, your shoes is riding on mucus.
Wow.
So where does this aquaplaning come from?
This is because the lubricant, the mucus
is compressed by the pressure we apply with our foot.
But since it's a little viscous, this liquid has a hard time escaping.
It will more or less stay put and that's what separates
the banana and the board.
This phenomenon, in English, is called the lubrication squeeze film.
In French, I don't know.
We also find it in most of our joints
which have a liquid inside the joint.
And when we apply pressure, the liquid remains contained inside
and helps lubricate the joint so that the bones don't come into contact.
Hence why I said that this topic brings together
two of my favorite subjects, mechanics and the human skeleton.
It's perfect. All that from a banana...
why not?
So in the end, we got the answer to Squeezie's and probably
many other people's question.
The answer being that the banana peel itself
is not really slippery, that much is true.
On the other hand, when you step on it,
that completely changes its properties.
The banana peel begins to produce a liquid that is quite viscous
and we end up going banana aquaplaning, which is why
it becomes extremely slippery; as slippery as skiing.
I'll try it now for real,
to see if in real life situation,
if it works.
But I don't want to fall.
So obviously this stone ground is a lot less slippery than if it were wood,
but that suits me because I really don't want to fall either.
It's slippery.
Ooh, a new camera with a good focus this time.
Alright, so
I've told you about all the very physics-based aspects of a banana slide.
And we could do the same exercise, but focusing on the miscroscopic
aspect of how the banana interacts with the floor
at a molecular or even at an anatomical level.
And we would be entering another area: the world of chemistry.
By the way, by the way, this video is sponsored
by the CNRS Institute of Chemistry, who just published
a science popularization book called Amazing Chemistry.
And it goes into a lot of everyday things, a bit like I do
on this channel.
But with a chemical approach.
For example: recently, we talked about fingerprints,
but I didn't get into the chemistry of fingerprint developers.
It's in there.
We also talked about how to extract energy from a burger.
There is a chapter on how to extract energy from sweat.
Or another chapter on batteries.
Look at this, this should remind you of something.
We did this experiment in the tears of wine video.
Well they go even further, but they focus on cosmetic chemistry.
Or here's another topic
which interests me a lot in the field of health:
they explain how to use chemistry in medical imaging
with what we call contrast agents
to see some things in the body
which would otherwise not be visible.
We haven't talked about that on the channel yet, but it's coming.
As you can see, this book covers many different subjects.
The chapters are short, 4-5 pages max.
In total, 54 topics are covered.
And the target audience is quite large: from early high school to adult.
It's co-written by many French researchers.
And if you're interested in what really happens
within matter, whether in current or future technologies,
you should get quite a few answers in this book.
Amazing Chemistry, Discoveries and promises of the 21st century at CNRS Éditions.
The link is of course in the description.
Thanks for watching this video.
I hope it made you want to subscribe
because I would really, really like
to cross the 500K subscribers milestone this year.
So please subscribe and spread the word.
Make it so that banana science is widely known.
Ok, bye.
Also, I changed something big in my video creation process
and I wanted to know: 1, did you notice it?
And if so, do you know what changed?
I'm curious.
Oh damn it's slippery!
It slips like crazy!