Friction



Friction is a non-conservative force, meaning that it's path-dependent, it's a contact force in physics and there are two different types: static friction and kinetic friction. Static friction is a frictional force that exists before the object moves. It has equal magnitude of the net force and has opposite direction of it. Kinetic friction is a frictional force that exists while the object is moving. Friction has a special relationship with normal force which also means that it is related to the mass of the object. When you do an experiment to figure out the relationship between these two forces and plot the data on the graph, you will see a line and the slope of that line is called the coefficient of friction, which is written as µ. The coefficient of friction depends on the type of surface. The coefficient of static friction is always bigger than that of kinetic friction because it is always easier to keep the object moving than to make it move from rest because the object has inertia. There are two formulas for friction.

Ffs ≤ µs Fn(perpendicular), Ffk = µk Fn(perpendicular)

If the magnitude of the net force exceeds the magnitude of the maximum static friction, the object starts to move. As soon as it starts to move, kinetic friction is applied to the object. It is also good to know that in order to accelerate you will need a net force or force greater than the friction (if the object is just on a flat surface).