Friction and Viscosity
Friction and viscosity are forces that resist motion and change. Minimizing these opposing forces in our environment reduces the energy required to achieve goals, and the relevance of these forces depends on the scale at which we operate.
THE IDEA
Energy is precious and we employ it sparingly. It’s human nature to allow the current state to remain as changing it requires us to expend energy. Getting started is the hardest part. Once something is moving in a direction, it’s much easier to keep it in motion. But once something is in motion, it’s hard to stop. The bigger the mass the more effort required.
Friction and Viscosity
Friction is a force that must be overcome to achieve an outcome. There is always something trying to slow us down.
While we can never eliminate the forces that impede our progress, we can work to minimize them. Like a smooth surface provides less challenge to a rolling ball, or how water is easier for a human to swim through than a krill, shaping our environment to reduce the challenges of opposing forces is a key to improving productivity.
Friction is a force that opposes the movement of objects that are in contact with each other, such as the wheels of a pair of roller skates moving across the ground. For objects to move, they must overcome friction that pushes in the opposite direction. This requires extra energy, which produces heat and sound. Smooth surfaces cause less friction than rough ones, which explains why walking on pavement is much easier and less tiring than walking on gravel. There are no frictionless surfaces, only surfaces with less or more resistance.
All objects experience friction. There are two key types of friction: kinetic and static. Kinetic friction occurs when two objects are sliding past each other. This explains why an object in motion, without consistent forces pushing it forward, will come to a halt. For example, if you place a book on a table and give it a push, it will move a bit then stop. The kinetic friction absorbs the energy you transfer to the book in the push. Static friction, on the other hand, occurs when an object is stationary; it’s what prevents it from moving.
Although scientists have been examining friction for about 600 years, there are still gaps in our understanding. Despite some of its mysterious qualities, friction remains a useful mental model because it captures how our environment can impede our movement.
Viscosity, which can be seen as the partner of friction, is the “measure of how hard it is for one layer of fluid to slide over another layer.” If a liquid is hard to move it is more viscous. If it is more viscous there is more resistance. Viscosity isn’t usually an issue for humans in our day-to-day lives. We have to deal with gravity and inertia, although viscosity is always present. But for small particles, gravity and inertia become a nonissue compared to viscosity. So if you make things bigger, viscosity is less relevant.
A tiny plankton moving in the ocean is going to have to struggle through the viscous water and will stop coasting forward almost as soon as it stops moving. For a whale, on the other hand, the viscosity of the water hardly registers. Its size means it can push water out of the way with ease, and capitalize on other forces such as inertia to keep forward motion.
There are two important aspects to using friction and viscosity as a model. First, what is easy in one environment might be harder in another. For instance, what we can accomplish in times of peace is different than what we can accomplish in times of war. Second, we also learn that the main forces relevant to a particular situation depend on the scale you are operating at.
—Sidebar: Surface Tension
When to use it
Process streamlining in business: Identify bureaucratic steps that create unnecessary friction for employees, then simplify or remove them to boost productivity.
User experience design: Reduce interface friction by minimizing clicks, load times, and confusing navigation to make desired actions effortless.
Personal habit formation: Lower the activation energy for desired habits by preparing the environment (e.g., laying out workout clothes the night before) to reduce static friction.
Scaling a startup: Recognize that what works for a small company (where interpersonal viscosity is high) changes as the organization grows, requiring different structures to manage inertia and communication.
FROM THEORY TO EVERYDAY LIFE
In practice
Plankton vs. Whale
A tiny plankton struggles against viscous water and stops almost immediately when it ceases movement, while a whale barely notices viscosity and can coast on inertia due to its large size. Scale changes which forces dominate.
Book sliding on a table
When you push a book on a table, it moves briefly then stops. Kinetic friction absorbs the energy from the push, converting it into heat and sound, demonstrating that objects in motion always face resistance until they stop.
Walking on pavement vs. gravel
Pavement is smoother than gravel, so it causes less friction. This explains why walking on pavement is easier and less tiring—reducing surface roughness minimizes opposing forces.
A MOMENT TO REFLECT
Put it to work.
What areas of your life have high friction that you could minimize by changing the environment?
How does the viscosity (resistance) of your current project or team affect momentum? What would need to change to reduce it?
Recall a time when starting was much harder than continuing. How can you apply the static vs. kinetic friction insight to overcome initial resistance in the future?
CONTINUE THE CONVERSATION
Source texts
- The Great Mental Models Volume 2 Physics, Chemistry and Biology