Types of Forces
- Static friction
- Frictional force between surfaces at rest with respect to each other.
- It increases with increasing applied force up to a maximum value (which is proportional to normal contact force).
- Kinetic friction
- Frictional force acting between surfaces in relative motion.
- Viscous forces
- Resistive force experienced by a solid moving in a fluid.
- Dependent on speed of object v, e.g. $$F_D\propto v$$ at low speeds and $$F_D\propto v^2$$ at high speeds.