The science of friction -- and its surprising impact on our lives

I have to admit that it's a lot of fun

when people ask me what I do for my job,

because I tell them
I literally rub things together.

This sounds ridiculous,

just rubbing things together.

But it has a technical name:

tribology.

T-r-i-b-o-l-o-g-y,

from the ancient Greek word "tribos,"

which means "to rub."

It's a funny-sounding word
you've probably never heard before,

but I promise you,

discovering it changes your experience
with the physical world.

Tribology has given me amazing projects.

I've worked on materials that fly,
and I've worked on dog food --

a combination that doesn't sound like
one person has any business doing

in the span of just a couple years,

until you start to view the world
through a tribological lens.

And I think you'll be surprised

at how significant
a little bit of tribology can be

in alleviating some very large problems.

Tribology is the study of friction,
wear and lubrication.

You have all experienced
all three of these things.

Remember the last time you tried
to move a heavy object across the floor,

and you can just feel
something resisting you?

That would be friction.

Friction is the force that opposes motion.

Wear is the loss or transfer of material.

It's the reason you have to replace
your favorite shoes,

because eventually the soles disappear.

Lubricants are used
to reduce friction and wear.

They loosen up those stubborn rusted bolts
that just otherwise will not budge.

But tribology is also defined
as the science of interacting surfaces

in relative motion.

So, interacting surfaces
in relative motion:

there are a lot of those in the world.

As you're sitting there right now,
are you wiggling your foot at all

or maybe shifting around in your seat?

Because guess what?
Tribology is happening.

Even the smallest shift in your seat

involves two surfaces
moving relative to each other.

And your tribological
interaction for the shift

will be different than
the person next to you.

This is because the clothes you're wearing

change the friction
between you and the seat.

If you're wearing silk, it's a little
easier to squirm around in the seat

than if you're wearing wool.

That's because the friction
is lower for silk.

If you're moving your ankle
or wiggling your ankle at all,

did it make a popping sound?

You've had that, right?

You get up, you move around,
and some joint cracks or pops.

Thank you for that sound, tribology.

That sound can come from the fluid
that lubricates your joints

just moving around.

You're essentially releasing
gas bubbles in that fluid.

That sound can also come from the tendons
simply moving over each other.

Pretty common in the ankle,

so any of my fellow
foot-wigglers out there

may suddenly find themselves curious
about the tribology of tendons.

But how does one become
a tribologist like me?

It starts when you're a kid, of course.

I was a ballerina growing up.

I reached the level
where I was dancing on my toes,

or "en pointe."

Now, when you're dancing en pointe,
you're wearing those amazing shoes,

but they can be slippery on the stage.

The last thing you want to do
when you're trying to dance on your toes

is to slip and fall.

So we had boxes of stuff called rosin.

We would step into the rosin,
put a light coating on our shoes.

Rosin comes from tree sap,

and in its powdered form,
makes things less slippery.

You learned real fast as a dancer

how much was the right amount
to put on your shoes,

because if you didn't put enough on,
you were probably going to slip

due to the low friction
between your shoe and the stage.

Best case scenario,

you're the clumsy ballerina on stage,

but the worst case scenario
would be an injury.

Already, I was optimizing
and manipulating friction.

You see, I was destined
to be a tribologist.

(Laughter)

But you were also a junior tribologist.

When you used crayons or colored pencils,

you knew that the harder you pressed,
the darker the color.

You also knew this meant
you were going to have to sharpen

that crayon or colored pencil
more frequently,

because it was wearing down faster.

Now let's talk about
those enticing shiny waxed floors

that you just had to slide across.

You knew if you put on a pair of socks,

you were going to get
a really good slide across that floor.

Good luck trying to do that barefoot.

Master manipulators of friction.

All kids are tribologists.

What about us as adults?

At some point today,
you brushed your teeth.

I hope.

(Laughter)

This is tribology in action.

The toothpaste and toothbrush
are working to remove or wear

the plaque from your teeth.

For the record, my dad is a dentist.

Never thought my career was going
to circle back to the family business.

But one day, we found ourselves
speaking the same language,

when I was tasked with developing a test
to investigate plaque removal.

Sounded simple enough,

until I started to look at it
as a tribologist,

and then it became incredibly complex.

You have hard materials --
those would be your teeth --

soft materials like your gums,
the toothpaste, the toothbrush.

There's lubrication --
the form of saliva and water --

the dynamics of the person
doing the brushing, and more.

I promise if we put diamonds
in your toothpaste,

you're going to remove that plaque.

Probably going to remove
your teeth as well.

So there's a fine balance to be had
between wearing the plaque away

and not damaging your teeth and gums.

We're brushing our teeth because we ate.

Eating is another routine thing we all do.

Seems simple enough.

But it's another field of tribology,

and it's not so simple.

You have the food, which will break
and wear while you're eating,

and that food is interacting
with your teeth, your tongue,

your saliva, your throat.

And all of those interactions are going
to influence your experience of eating.

I think you can all recall a moment
where you tried something new

and you just found yourself going,

"Well, it tastes alright.

I really don't like that texture."

Tribologists are looking at lubricity
and coefficient of friction

as ways to connect mouth feel
and texture to what you're experiencing,

so that if we're changing the formulations
of what we're eating and drinking

so the sugar content
or fat content are different,

how does that change mouth feel?

How do we quantify that?

This is what tribologists
are looking to solve.

And while my colleagues
were in one corner of this lab

looking at the fat content of yogurt,

I was in another corner,

studying dog food.

That lab smelled really good,
by the way, let me tell you.

We all brush our teeth on a regular basis.

How many of us brush our pets' teeth?

Animals as adults commonly get
periodontal disease,

so we really should be
brushing their teeth,

and more pet owners
are starting to do this.

I know my best friend is really great
at brushing her cat's teeth, somehow.

Good luck trying to do that with my cat.

So what pet food suppliers
are trying to do

is incorporate plaque removal
in things like treats.

If you have a dog,

you may have observed
that you give a dog a treat,

and it magically seems to disappear
after just one bite.

So the added challenge here is:

How do you remove plaque
when you have one bite?

I developed a benchtop test
to study this problem,

and to do so, I had to mimic
the oral system of dogs:

their teeth, plaque, saliva.

And I used friction and wear measurements

to study the effectiveness
of that treat on removing plaque.

If you're sitting there right now
thinking about the last time

you didn't brush your dog's teeth,
you're very welcome.

But what's the big deal with tribology?

Let me give you one more example.

No matter where you are right now,
you got to this location somehow.

Maybe you walked or rode your bike,

but for most people in this room,
you probably came in a car.

Just think about all
the tribological systems in a car.

You have your personal
interactions with the car,

the car's interactions with the road,

and everything under the hood
and in the drivetrain.

Some routine maintenance
is directly connected to tribology.

You know how many miles
your tires are recommended for using

before you replace them.

You regularly check
the treads on those tires.

You're actively monitoring
the wear of your tires.

Tribology is the study
of wear and friction,

and with tires, friction can be
the difference between a safe arrival

and a car accident.

This is because the friction
between your tires and the road

will influence your acceleration,
your deceleration

and your stopping distance.

As a driver, you instinctively
already know how important friction is,

because you know
that when the roads are wet,

they're more dangerous
because they're slippery.

This is because the water
is reducing the friction

between your tires and the road.

You may recall that friction
is the force that opposes motion,

so water reducing that force
means it's now easier for you to move,

hence it's more slippery
when the roads are wet.

Something else to consider

is that overcoming friction takes energy,

so you're losing energy to friction.

This is one way your tires
can influence your fuel efficiency.

And, in fact, did you know
that about one-third of the fuel

that you put into your
internal combustion engine vehicle

will be spent overcoming friction?

One-third.

Tribology research
has helped us reduce friction

and therefore increase
fuel efficiency and reduce emissions.

Holmberg and Erdemir have actually
done some great studies

showing the impact
tribology research can have

on reducing our energy consumption.

And they found that, looking over
the span of 20 years,

we had the opportunity to reduce

the energy consumption
of passenger vehicles

up to 60 percent.

When you think about
all the cars in the world,

that's a lot of energy we can save.

It's part of the nearly nine percent
of our current global energy consumption

that the authors identified
tribology can help us save.

That's a significant amount of energy.

So when you look at the numbers,
tribology can do some amazing things.

My colleagues have identified
up to 20 quads of energy

we can save across the US alone.

To put this in perspective:

one quad of energy is roughly equivalent
to 180 million barrels of oil,

and tribology can help us
save 20 times that.

This is through new materials,
new lubricants,

novel component design,

doing things like making wind turbines
more efficient and reliable.

This happened just by putting
31 people in a room

who viewed the world
through a tribology lens.

Imagine the opportunities
that will reveal themselves

as more of us start to see
tribology all around.

My favorite projects right now
are in aerospace applications.

I love reducing wear and friction
in these challenging environments.

I can make materials and parts

that will reduce the friction
in moving components and engines

so that they have less force
opposing their motion.

Less force to move
means they require less power,

so you can use a smaller actuator,

which would weigh less,

which saves fuel.

I can also help make parts
that last longer through lower wear.

This will reduce material waste

and also means we're manufacturing
the parts less frequently,

so we're saving energy in manufacturing.

I encourage you to start seeing
tribology in the world around you

and to think about how you would improve
those interacting surfaces you experience.

Even the smallest improvements

really add up.

Tribology may be a funny-sounding word,

but it has a huge impact on our world.

Thank you.

(Applause)