Understanding Friction

Friction plays a role in every mechanical system. Whether it's gears meshing, pistons sliding, or bearings rotating. Anytime two surfaces contact each other, friction is there resisting motion whether you want it to or not. But what exactly is friction? What causes it? And how can we use it to our advantage? Let's find out. At the most

basic level, friction is a resistive force that acts whenever surfaces are in contact and there's relative motion or attempted motion between them. Consider a block resting on a table. If you push on it with a small amount of force, it doesn't move because a friction force develops at the interface between the two surfaces, exactly

balancing the applied force and preventing the block from moving. As you increase the applied force, the friction force increases too up to a limit. Push beyond that limit and the block starts sliding. Let's plot this relationship between friction and the applied force. The friction force increases linearly as the applied force increases up to a

maximum value. Any additional force causes the block to slide and once it starts moving the friction drops to a lower roughly constant value. There are two different friction types, static friction and kinetic friction. It takes more force to start motion than it does to maintain it. So what causes this resistive force between the two surfaces? It turns out

friction is the result of some quite complex interactions that occur at the microscopic level. Even the most smooth seeming surface, if you zoom in close enough, is covered in microscopic peaks and valleys called asperities. When two surfaces are brought together, it's these asperities that make the first points of contact. Because the load is supported by just a