Traction!

In conversations, few words catch my attention faster than ‘friction’ – and especially talk of making things frictionless. From the workplace to grocery shopping, our societies seem to be striving to remove friction from everything. The motivation appears to be that decreasing resistance makes life easier and smoother.

Having spent a career as a tribologist, studying friction, wear and lubrication scientifically, I have some opinions on this. I’ll confess that, in most of my career, I too have sought to reduce friction, developing new materials, designs or even instrumentation in order to lower friction in a jet engine or reduce emissions from your car. However, I’ve also found myself trying to figure out how to increase friction to remove plaque on teeth.

The reality is that friction, despite seeming so antagonistic, is necessary and even productive. The force that resists motion has, since humans first struck a spark from a stone, been the very thing that propels us forward. And this paradox offers a lens through which to reread humanity’s entire technological history.

In order to appreciate all that an understanding of friction has helped us to accomplish, it’s necessary to start at square one and state what friction actually is. We define friction as the force that resists motion, and that means friction is rather ubiquitous. If things are moving, whether they’re sliding around or rolling, there’s friction. Solids, liquids, gases? Doesn’t matter. If there’s movement, friction is there to resist it. Unfortunately, because friction’s job is to resist, we’ve developed an aversion to it as a nuisance. But it’s a very important force, and we’ve thrived by expanding our understanding of it. By the 1960s, after millennia of evolving with friction, we finally accepted that friction is such a critical part of our world that a scientific field of study needed to be devoted to it: tribology.

Tribologists like me study this force in all its forms. Tribology is the science of interacting surfaces in relative motion, concerned with the wear of materials, friction and lubrication. Basically, tribology is the specialisation of things rubbing against each other. You may raise an eyebrow at a field of science focused on this, but when you pause to consider how much motion is going on inside us, around us and throughout the Universe, you can appreciate that tribology is vast. More than anyone, tribologists know the problems friction can cause. But they also know the achievements that have followed as we’ve come to understand resistance better.

Although tribology as a formalised field is relatively modern, friction has long shaped humanity’s technological innovations. For example, consider its pivotal role in people’s journeys from A to B over the centuries. I’m willing to bet that whenever you need to move unwieldy furniture or carry home that giant bag of cat litter, your instinct is to find a cart to help you. Early humans had a similar thought, turning to log rollers to move heavy objects, and coming up with one of our greatest inventions: the wheel. Rolling makes it easier to move objects because it reduces friction between the object and surface you’re moving it against. There are far fewer surface interactions in the process of rolling versus sliding. Plenty can be said about the wheel, including the fact that even in 2026 we can’t seem to agree on the origin of its discovery, but there is zero doubt that it’s a brilliant innovation for dealing with friction. But wheels also need friction: when we exert a force to move a wheel forward, the force between the ground and the wheel – static friction – keeps it from spinning freely, which would result in us going nowhere. Once forward motion begins, the resistance to motion becomes dynamic friction, which is just as important. If you’ve driven on ice, you know the danger of too little friction.

However, if people hadn’t continued improving on these basic principles, even the wheel would be rather inefficient due to friction.

The Vikings’ longships minimised form drag so they could cut through the water quickly

The ancient Romans discovered this in their amphitheatres. Roman chariot races didn’t come without their headaches. Or rather, foot aches. I’m certain the drivers likely complained about their hot feet, caused by friction between the wheels and axle heating up the surrounding parts. In Odes, a collection of lyric poems, the poet Horace described how chariot wheels would glow during racing. Today, scientists know that this glow is from turning the energy of motion into thermal energy. Roman designers eventually figured out that they could temper the problem by putting axungia (animal fat) grease between the wheel and axle. By doing so, they were applying tribological knowledge already exploited by the Sumerians: that fats and oils work more effectively than water as lubrication between surfaces. However, that created a new conundrum: if the grease got hot enough, it risked catching fire. The solution? A coolant. In this case, they splashed water on the chariots, in the ancient equivalent of a pit stop.

While all roads led to Rome, you could say all seas led to the Vikings. They, too, cleverly adapted to the resistance that met them as they journeyed through the oceans. Moving through fluids produces a type of friction known as drag. Even within drag there are subsets. Skin drag is from the friction between the surface of the ship and the water, whereas form drag stems from the shape of the hull as it moves through the water. When they had to transport cargo safely, the Vikings used sturdy ships with wide hulls. This wider hull increased form drag and slowed them down, but the stability provided was more critical. Their famous longships, however, were long and slim, minimising form drag as much as possible so they could cut through the water quickly.

As with all friction scenarios, however, the Vikings found themselves having to balance some competing demands. Faster longships are better, yes, but it was also imperative that the ships not break apart into pieces from the waves. They needed flexibility and strength, while keeping the ships as light as possible to ride higher in the water to reduce drag. To do this, the Vikings used their ‘clinker’ technique of nailing together long planks of wood. The rivets and overlapping planks would increase drag compared with a more polished, smoother design but these individual planks gave the ships the ability to twist and flex to weather storms. If I was on a boat trip in the middle of the ocean, I too would be happy to sacrifice a little bit of drag reduction to avoid capsizing from a rogue wave.

Looking at boats and ships today, it’s clear that we didn’t just accept these Viking designs as the culmination of nautical perfection. Likewise, we aren’t driving around in Roman chariots today. We have since made incredible leaps forward in understanding how to quantify friction and thus design for it, finally approaching friction scientifically. In the 1920s, Chrysler’s head of engineering Carl Breer had the idea to design cars with aerodynamics in mind. Planes seemed to slice seamlessly through the air. Shouldn’t cars do the same? Breer tasked the engineer William Earnshaw to consult with none other than Orville Wright to learn how to design a car in a wind tunnel. The resulting teardrop-shaped Chrysler Airflow was considered a flop, as many disruptive designs can be when they’re just too jarring for taste, but that flop revolutionised how we design cars. Wind-tunnel testing remains a standard today, and friction’s presence is as expected as the air itself.

Tribology testing is routine for the automotive industry today, and there are tribology labs scattered throughout a variety of industries, from medical to food. In these labs, you’ll find instruments designed to measure friction at macro-scales down to the atomic level. My PhD lab at the University of Florida had tribometers measuring friction in force ranges that covered three orders of magnitude. I’ve even worked in a lab that had a tribometer built to test an actual train wheel against a railway. Tribologists are incredibly clever with innovating ways to measure friction, given how persnickety friction is. Friction is dependent on the conditions of the operation – how fast things are moving, how much force they experience, and what temperature and environment they’re in.

Temperature in particular is a fun variable to contend with, because friction itself leads to temperature changes; indeed, frictional heating can be extreme in some cases. Like with Roman chariots, greases can ignite at certain temperatures making it imperative to control friction heating in order to avoid accidentally reaching that temperature. And for applications like jet engines, which get very hot anyway, we have engineered solid materials with low friction to withstand the heat.

When tribologists run into a wall, we develop a new instrument to understand what friction is trying to tell us

You may think tribology is already a niche field, but we have specialisations within it. Mine was solid lubrication, and I worked on developing and testing materials for jet engines and automobiles. In some cases, the conditions of the end use were so aggressive that the steel I was running my material against would experience enough friction heating to completely change the colour of the steel. That’s how you know you’ve reached the extremes in tribology, but those extremes must be met and they obviously are. After all, we have space stations orbiting Earth and landers on Mars.

Which brings us to another critical point about friction’s role in human progress: resistance is a consequence of progress, and its existence is a sign of progression itself. We wouldn’t have the now-robust business of solid lubricants if we had not advanced technologically to design turbine engines, which themselves were the result of us figuring out powered flight. By achieving that, our progress led us to new resistance. I think this is critical to remember anytime we find ourselves confronting unexpected resistance, and it’s something I remind myself of whenever I get halted in my work. I wouldn’t be stumped by this new resistance if I hadn’t managed to advance myself to this position where the resistance exists.

Often when tribologists run into a wall, we find ourselves developing a new instrument to help us understand what friction is trying to tell us. Tribometers have been designed to mimic all of the variables mentioned above, and that alone is quite a feat of human engineering, but now we also couple them with other techniques that allow us to somehow see what is happening while it’s happening. From maps of frictional heating during operation to how friction is influencing cellular movement, instruments and techniques have enabled us to usher friction into a new era to drive us forward, doing more than just finding clever ways to overcome friction. We can harness it as a tool.

In terms of friction, the 20th century can be thought of as the century in which humans accepted the resistance, and established engineering rigour around friction to propel our technological advances forward. Critically, it’s when we formalised how to overcome friction to be more efficient. As a tribologist, however, I’m far more excited about what the 21st century has brought us. Instead of just overcoming friction, we began fully realising how to harness that resistance to bring in a new era of progress. Exhibit A is once again found in our cars, where friction has been deployed as a tool in sustainability. Braking requires friction, so engineers asked: why don’t we use the consequences of that friction to our advantage? The heat from friction in braking is now used to create electricity in regenerative braking in EVs and hybrids. We must continue to use this creative and fresh perspective when dealing with friction, as opposed to always driving towards frictionlessness. Imagine if those engineers had been so fixated on the negatives of friction that they didn’t harness its power.

Using friction as a tool has come to us only as we’ve evolved to understand the depths of friction, including its behaviours and where it may be lurking. We know it is involved in dynamic processes, so let’s use it to control such processes. Yes, we’ve done so for a while with mechanisms like brakes and dampeners, but expanding this beyond machines has really taken hold in recent decades. Now, we’re looking at how friction may be a tool in perhaps the most impressive machine there is: the human body. It’s possible friction may be a lever to help us better model and understand biological processes and, in turn, help in the development of therapeutics. The rate at which a virus ejects from its protein shell or capsid can dictate whether it results in an active infection or instead remains dormant in the cell. If we want to use viruses to intentionally infect and defeat other viruses or bacteria, then controlling the virus’s ejection rate is crucial. Friction is the key to unlocking this possibility. In 2023, researchers found that, by packing the coils of virus DNA in certain ways, they could increase friction during ejection and slow down its rate of ejection.

Every advance we make generates new friction. We solve one problem, and friction presents another

Recently, our knowledge of friction has taken us to even more surprising places, extending even to helping us understand dark matter. The concept of ‘resistance is your reward for progress’ may be best illustrated by the astrophysicist Subrahmanyan Chandrasekhar. Despite the fact that established scientists mocked his theories, Chandrasekhar would go on to become a founder of astrophysics, and is the reason we understand the evolution of stars and interstellar dynamics. In the 1930s, he was interested in how the interactions between stars could lead to their collisions. He calculated the timescales of such collisions and realised, though only after publishing, that things weren’t adding up quite right. This led him back to the drawing board, where he spotted there was a resistance present that no one before had identified: dynamical friction. This friction is a gravitationally induced drag that acts on objects as they interact and move through space.

Fast-forward to the 21st century, and dynamical friction has been used as a tool to infer the presence of dark matter. In 2024, researchers in Hong Kong realised that orbital times weren’t matching up with a couple of stars they were studying that were believed to be circling around black holes. They looked at Chandrasekhar’s concept of dynamical friction and wondered what would happen if they incorporated the contribution of friction from the dark matter surrounding the black hole. Voila! Suddenly, the predicted and calculated orbital times of the stars matched with what they were measuring. Friction was present when humanity first started experimenting with fire and the wheel. Now it’s there as we probe the frontiers of our Universe.

We need friction to move. Without its resistance, Earth’s plates would be in constant motion. We could not walk, or drive, or even hold objects. Understanding how to achieve what we want, in a world requiring this resistance, has been essential in our development.

Yet there is a deeper paradox at work, one that William James captured when he wrote that life is built ‘in the self-governing resistance of the ego to the world’. Every advance we make generates new friction. We solve one problem, and friction presents another. We step forward, and new resistance awaits. This is what progress means: that we have moved into territory that demands new understanding.

Roman engineers learned it when their chariot wheels caught fire. Chandrasekhar discovered this when his calculations didn’t add up. And we will continue to encounter resistance as we push forward.

When people speak of a frictionless world, they imagine ease. But ease without resistance is a wheel spinning in place, motion without progress.