Which of the following types of friction is associated with physical barriers or opposition?

The correct answer is physical friction because it refers to the resistance encountered when objects interact with one another due to their surfaces. This type of friction is generated through tangible barriers or opposition within a physical context, such as surfaces rubbing against each other. Physical friction plays a crucial role in many aspects of movement and interaction in the physical world, as it can slow down or halt motion.

In contrast, the other types of friction mentioned do not correspond to this tangible sense of resistance. For instance, mental friction pertains to cognitive or psychological barriers that can inhibit thought processes or decision-making, rather than a physical interaction between surfaces. Internal friction generally relates to forces or resistances within a system, such as within a fluid, which does not address the direct opposition found in physical interactions. External friction might suggest forces acting from outside but is not a standard term used in physics to describe the direct interaction between physical barriers. Thus, physical friction distinctly captures the essence of friction as a result of contact between tangible objects or surfaces.