Friction is the opposing force that comes into play when two bodies come in contact with each other. According to classical theory, friction is caused due to the welding effect. While modern theory suggests that friction arises due to the adhesive and cohesive force between the molecules and the pressure exerted by the body.
Types of friction:
Static friction: The friction which acts until the body is at rest is called static friction. Static friction is also called self adjusting force because it has neither fixed magnitude nor direction and hence adjust according to the applied force. and it is the strongest type of friction.
Kinetic friction: The friction which comes into play between two surfaces when one body is slided over another body is called kinetic friction. Kinetic friction is also known as sliding friction. Kinetic friction is always less than limiting friction. Kinetic friction is required for a body to bring a moving body into rest.
Rolling friction: The friction which comes into play when a body rolls over the surface of another is called rolling friction. It is always less than rolling friction. This friction is required to stop the rolling body.
Fluid friction: The frictional force that comes into play when a body is moving through a fluid is called fluid friction.