1. **Problem statement:** A 4 kg block rests on a horizontal surface. A force vector $P_N$ acts at an angle of 30° above the horizontal. The block is on the verge of sliding. We need to determine the direction of the friction force. 2. **Understanding friction:** Friction always acts to oppose the relative motion or impending motion between surfaces. Since the block is about to slide, friction acts in the direction opposite to the impending motion. 3. **Analyzing the force direction:** The force $P_N$ is angled 30° above the horizontal to the right, so it tends to move the block to the right. 4. **Direction of friction:** Since the block tends to slide right, friction acts to the left along the horizontal surface to prevent sliding. **Final answer:** The friction force acts horizontally to the left, opposite to the direction of the applied force $P_N$.