The reason this occurrence with friction happens is B. The force of friction is always equal to our applied force, resulting in no net force and therefore no acceleration.
When we walk, the force of friction between our feet and the ground provides the necessary opposing force to move us forward. In simple terms, our muscles exert a force on the ground, and the ground exerts an equal and opposite force (friction) on us, following Newton's third law of motion.
This equilibrium of forces means there is no net force acting on us, resulting in no continuous acceleration. While there may be slight variations in force as we walk, these are not significant enough to cause noticeable, continuous acceleration. Therefore, we don't keep accelerating while walking, and we maintain a relatively constant speed.
Options are:
We are constantly accelerating when walking, but it's imperceptible due to the small magnitude of the acceleration.
The force of friction is always equal to our applied force, resulting in no net force and therefore no acceleration.
Walking involves a series of alternating forces, so we do experience continuous acceleration.
The force of gravity counteracts the force of friction, preventing continuous acceleration.