Which of the following is NOT a type of friction?

Friction is a force that opposes the motion of objects in contact with one another. There are several recognized types of friction based on the nature of the movement and the interaction between surfaces.

Static friction occurs between surfaces that are not moving relative to each other. It is the force that prevents an object from starting to move when a force is applied.

Sliding friction, which can also be referred to as kinetic friction, acts between surfaces that are sliding against each other. This type of friction is typically less than static friction, making it easier for objects to continue moving once they are in motion.

Fluid friction, or drag, pertains to the resistance experienced by objects moving through fluids, which can be liquids or gases. This force becomes significant when considering objects like boats moving through water or airplanes flying through the air.

In contrast, frictionless refers to an ideal scenario rather than a type of friction. In reality, all surfaces experience some level of friction unless they are in a vacuum or otherwise specifically engineered to minimize it. Thus, defining a condition as "frictionless" does not classify it as a type of friction.

Understanding these distinctions helps clarify how different interactions between surfaces affect motion in physical science.