'Do not stack'. ('to stack' also means 'to vomit' in French)
If you have already worked in handling, you know that 'do not stack'
has nothing to do with the action of vomiting.
'Do not stack' means: do not stack packages on top of each other.
The underlying reason is more complex than it appears and is intrinsically linked
to this: the corrugation of cardboard!
It was estimated that Amazon handled 5 billion shipments via its Premium program in 2017,
most of which were packages.
We could wrap the Earth more than 570 times over with all the cardboard we have.
The design of a cardboard box is a science that links pizza holding techniques
all the way to he structure of a bridge. By the end of the video, you will know why it is forbidden to stack.
Before the creation of corrugated cardboard, we would send packages in wooden boxes.
Very heavy, not adaptable, expensive... in short not very practical.
But back then every package really mattered.
We didn't get your toothpaste that way.
The inventor of corrugated board was inspired, it seems, by the fashion of the 19th century
which was all about frills.
Cardboard frills served as reinforcement to maintain the shape of top hats.
Fashion can therefore inspire inventors to innovate in the industrial sector.
I am curious to see what inventions today's fashion will inspire.
Albert Jones filed the first patent on corrugated cardboard in 1871
in order to pack fragile materials such as glass bottles.
The cardboard was composed of a single flat surface
stuck to a corrugated surface, or flutes.
You can find flutes on a 'canelé de Bordeaux' or on
certain metal sheets.
Since then, we've created tons of new types of corrugated cardboard:
single face, single wall, double wall, triple wall... with many variations in thickness too.
Each type of cardboard is defined according to its grooves because they each have
"a je-ne-sais-quoi...
...that others don't have"
Let me explain.
Let's take a slice of pizza (which also comes in a corrugated cardboard box).
If you hold your pizza without doing anything special
it bends under its own weight
and the toppings fall off, which is a shame since that's the best part.
The way to counter this, as I'm sure you all know,
is to fold (or flute!) the pizza crust in the middle
and the pizza slice becomes magically rigid.
We basically created a groove.
In short, a simple action of the hand can help to stiffen an elongated shape like this.
There are many ways to explain mathematically or physically how a curvature can
rigidify a whole object but we will keep it simple.
The thicker an object, the harder it is to bend.
When we fold the crust of our pizza slice, we increase the thickness
or rather we reorganize the matter so as to have more along the vertical axis,
but that sounds a bit more complicated.
So by adding grooves to cardboard, it becomes thicker
and more stiff, which means it can better withstand a whole set of strains.
Let me explain.
I'm going to need...
The FX team has worked hard on this video...
Let's stop talking about pizza and get back to the stacking problem.
Once the boxes are stacked, their vertical sides have to withstand the weight coming from above.
That's called buckling (also means 'burning' in French).
It has absolutely nothing to do with fire.
Buckling relates to the reaction of a material when it is strained to the point
of instability, like when I compress this spaghetti.
When the pressure and instability get too high, it breaks.
The critical buckling force is proportional to
something called the quadratic moment
noted capital I.
The quadratic moment represents the distribution of the mass around an axis
(in our case that's the axis around which the cardboard bends).
When more matter is distributed far from the axis, the quadratic moment increases,
which means that moving all this material around the axis is more difficult.
So what that means
Tssst, don't talk with your mouth full.
So one material can have a different structural stiffness depending on its shape.
I say stiffness and not rigidity because they are different things.
(at least in French)
Small aside...
Cardboard, the material itself, regardless of shape, has a certain rigidity.
It's not very high (obviously)
but it is defined by its Young's modulus noted E.
But the stiffness of cardboard, once folded to make corrugations,
its structural stiffness if you like,
depends both on Young's modulus (the characteristics of the material),
and on the quadratic moment (the shape of the material).
Aside over...
The force required for my spaghetti to buckle
also depends on the stiffness of the material
which we represent with E*I.
The greater the rigidity,
the greater the necessary force to induce buckling.
That's why trying to buckle a rotini or a spaghetti is very different.
For corrugated cardboard, the formulas are more slightly more complex
but the geometry of the material always matters for its resistance.
In short, the 'do not stack' notice is there because cardboard boxes
weren't designed to withstand heavy loads...
... or to prevent boxes from being handled without care.
But there is something more. It isn't written 'do not stack' on every cardboard box.
It is mostly written on very tall boxes.
This is because the taller an object,
the smaller the buckling force.
The quadratic moment is not enough.
Size also matters.
You'll notice that in this formula, the weight of the material is not considered.
So by keeping the inside of a cardboard surface empty and filling it with grooves,
we obtain a stiffness equivalent to that of a full cardboard surface.
This saves a lot of material which is great both economically and ecologically.
Small aside...
FYI, if you take an average box (30cm x30cmx30cm) and an average tree,
we build about 152 boxes per tree.
In 2010 in the US, it was estimated
that each person consumed 1.5 tree per year, *just* for cardboard boxes.
Since corrugated cardboard gets recycled very well
and that our consumption of it is kind of absurd,
do put it all in the recycling bin, it's worth it ;)
Aside over...
Aside from stacking boxes, grooves perform great under pressure.
When a force is applied to the cardboard, it is transmitted along the corrugations
which compresses them all along their length.
When the compression is too strong,
the flutes buckle as you can see here.
So corrugated cardboard has an integrated shock absorbing system.
Apart from cardboard, you will find a similar type of structure in bridges.
The folds aren't called 'grooves' but the principle is the same.
This shape helps distribute its mass across the entire bridge
and avoid (or reduce the risk) of this happening...
Such bridges appeared only 50 years before the invention of corrugated cardboard.
Who knows, it may not be a coincidence...
Next time you receive a package, look at it closely --
you'll see it in a whole new light.
--- Ok, time for a confession.
Originally, I wanted to make a short bullsh*t-y video just to restart the algorithm
and to talk about the fact that we passed 100,000 subscribers
because it's cool and because YouTube sent me a plaque to celebrate it.
But I got carried away.
In preparation for this bullsh*t video, I started reading
all about the cardboard that carried the Play button
but it turned out to be way more interesting than I thought it would be.
So this isn't a bullsh*it video after all
but one with some science in it.
Even better ;)
Thank you all for being here still, I know I took a long break.
Well, it looked like a break to you, but it wasn't really.
So please share this video because after spending so much time away,
YouTube is a little upset and resents me a little,
so I'm counting on you to compensate.
See you soon
Bye.