Frictional force is the force generated by two surfaces that contact and slide against each other. It is a contact force that opposes motion and decreases the mechanical advantage of a machine. The factors affecting frictional force include the surface texture, the amount of force impelling the surfaces together, and the angle and position of the object. There are different types of frictional forces, including static, kinetic, rolling, sliding, and fluid friction.

• Static Friction: This type of frictional force is experienced when we try to bring a stationary body to motion on a surface without stimulating a relative motion across the surface. The static frictional force is a little different from the kinetic frictional force. For one, the static frictional force will change its value based on how much force is being applied to the unbudging object.

• Kinetic Friction: This type of frictional force occurs when two surfaces are sliding past each other. The force of kinetic friction always opposes the sliding motion and tries to reduce the speed at which the surfaces slide across each other.

• Rolling Friction: This type of frictional force occurs when an object rolls over a surface.

• Sliding Friction: This type of frictional force occurs when two surfaces slide against each other.

• Fluid Friction: This type of frictional force occurs between fluids and gases.

The frictional force is proportional to the normal force exerted between the surfaces. The value of the coefficient of friction for a case of one or more objects sliding on a surface depends on the texture of the surface and the amount of force exerted on the objects. The unit of frictional force is the same as force, which is Newton (N), and its dimensional formula is .