This video is sponsored by the Rubber Division of ACS.
Watching your favorite team throw the pigskin around is an autumn weekend ritual -- but
there’s something they don’t want you to know.
As much fun as some people have watching guys in tights fight over who gets to hold a weirdly
shaped hand-egg, they’re LYING to you.
That’s right -- footballs aren’t made of pigskin(1).
Instead, sports balls of all varieties owe their resilience and reliability to an unusual
polymer, one whose derivatives and spinoffs are everywhere you look, from cars to shoes
to rocket fuel.
Yes, rocket fuel.
Meet the all star’s best friend: Rubber.
For hundreds of years, indigenous peoples of Central and South America like the Olmecs
have known that you can extract a stretchy, bouncy substance from the sap of certain trees,
most notably Hevea brasiliensis.
This is natural rubber latex.
The sap contains polyisoprene, which is processed into natural rubber, or dried and used as
latex for things like surgical gloves.
The polyisoprene strings are springy and flexible, giving rubber its stretchy properties.
Natural rubber has some flaws.
It flows readily at high temperatures and becomes rigid when it’s cold.
That’s because the long strings of polyisoprene are free to flow past each other inside the
rubber, so they can ooze or solidify like any other substance.
Charles Goodyear found in 1839 that adding sulfur to rubber, then heating the mixture,
causes a chemical change to take place.
Atoms of sulfur form bridges between the polyisoprene chains, linking them together.
They can no longer drift past each other.
The flexible polyisoprene and tough sulfur cross-links strike a balance between flexibility
and rigidity that are the key to rubber’s bouncy, stretchy properties.
It can deform, but return to its original shape time and time again.
Like stretch armstrong.
Remember him?
When rubber became temperature-resistant, aka ‘vulcanized’, that was its chance
to take over the world.
Not only was it suitable to be made into tires; it could also be used to make engine turn
belts and seal up gaps, even at high heat.
Yup, rubber totally made cars a thing.
But its cultural awesomeness doesn’t end there.
Most rubber these days isn’t derived from trees.
There are dozens of kinds of synthetic rubber, and even more kinds of not-rubber-but-still-kinda-stretchy-and-useful
materials, made from petroleum.
One kind of synthetic rubber, polysulfide rubber, or Thiokol is even used to bind rocket
fuel together.
But back to sports, because we know that’s what you really watch science videos for.
Most of your good ol’ sports balls are going to have some rubber in them, or one of those
similar stretchy substances.
Footballs contain an air bladder made of polyurethane, surrounded by leather made from cows -- not
pigs.
Originally, footballs were probably made of animal bladders, which might actually have
come from pigs -- but that’s still not their skin.
Rubber and then urethane replaced the bladders -- to the pigs’ relief.
And while rubber or urethane holds its shape, animal bladders don’t.
It’s possible that the pointed shape of modern footballs is just because the animal
bladders were so wonky they gave up on trying to have a round ball.
How much rubber is in the ball affects what it can do.
This tennis ball is filled with air, which is easily compressed, so it smushes flat when
it bounces.
The rubber snaps the ball back into shape, but that requires energy.
So some of the energy the ball had on the way down is lost on the way back up.
A super ball, on the other hand, is one giant chunk of polybutadiene-- another synthetic
rubber.
And the whole thing is vulcanized.
The tough sulfur bridges prevent the ball from losing its shape too much, and most of
the energy carries over to the next bounce.
Basketballs bounce much like the tennis ball, but the NBA apparently favors natural rubber
and leather.
And baseballs need to fly when you hit them, but not so far that every hit is a home run.
So while they have a rubber core, it’s wrapped in string to deaden the bounciness a little,
then in leather for grip.
So there you have it: All your fave sports rely on rubber,
or rubber-ish things, to make the play.
And you need rubber to drive to the ball park and rubber to fly to space to watch space
volleyball.
I made that one up, but how dope would that be?
Thanks to the Rubber Division of the ACS for making this video possible.
Engage with them at rubber.org to learn more about elastomer science, and to find out how
to become part of this community.
Sound off in the comments, and be sure to hit like and subscribe as you’re scrolling
down.
See you out there, sports fans.
And hey, thanks for watching.