When a person walks on a rough surface, the frictional force exerted by the surface on the person is opposite to the direction of his motion.

Step 1: Analyze the mechanics of walking.

When a person walks, their stance foot pushes the ground backward.

$$\vec{F}_{\text{foot on ground}} \text{ is directed backward}$$

Step 2: Apply Newton's Third Law to find the direction of friction.

By Newton's Third Law, the ground exerts an equal and opposite reaction force on the person. Since there is no slipping at the point of contact, static friction opposes the relative tendency of the foot to slide backward.

$$\vec{f}_{\text{ground on person}} \text{ is directed forward}$$

Since the person moves forward, the frictional force acts in the direction of motion.

Step 3: Analyze the forces using a Free Body Diagram (FBD).

In the vertical direction, the normal force balances the weight.

$$N = mg$$

In the horizontal direction, the static frictional force $f$ is the net force causing forward acceleration $a$.

$$f = ma$$

The maximum possible acceleration is determined by the coefficient of static friction $\mu$.

$$f_{\max} = \mu N = \mu mg$$ $$a_{\max} = \mu g$$

If $\mu = 0$ (a perfectly smooth surface), then $f = 0$, meaning no forward force can be exerted and walking is impossible.

Step 4: Distinguish between walking and sliding.

The behavior of friction depends on the type of contact:

• For sliding, kinetic friction opposes the direction of motion.
• For walking, static friction prevents slipping and acts in the direction of motion to propel the person forward.

Answer: The statement is False. The frictional force exerted by the surface on a walking person acts in the direction of motion, not opposite to it.