# 04. Forces

### 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.
https://physicslens.com/04-forces/