Force of friction always:

The force of friction is a resistive force that always acts in the opposite direction to the applied force when an object is in motion or when a force is attempting to cause motion. This means that if you push an object to the right, the frictional force will act to the left, thus opposing the applied force.

Friction arises due to the interactions between the surfaces in contact, and it serves to resist the relative motion of those surfaces. In practical terms, it is essential for many everyday processes, such as walking, driving, and holding objects in place. Understanding this fundamental characteristic of friction is crucial in the field of engineering, as it directly affects calculations related to force, motion, and the design of mechanical systems.

The other aspects mentioned in the choices provide interesting information about friction but do not define its fundamental nature concerning the applied force. For example, friction does not travel with the applied force; instead, it acts against it. While the contact area can influence the magnitude of friction, it does not dictate its directional nature. Furthermore, friction typically only exists when there is some force applied to create that interaction; hence, it does not normally exist without an applied force.