Walking becomes difficult, When the ground is covered with snow or sand this is because

Explanation

### Step-by-Step Solution:

1. **Understanding the Surface Interaction**:
- When walking on a solid, stable surface (like concrete), the foot exerts a downward force on the ground. According to Newton's third law, the ground exerts an equal and opposite force back on the foot, allowing for effective propulsion and movement.

2. **Analyzing the Effect of Snow and Sand**:
- On surfaces like snow or sand, when a person steps down, the foot pushes into the material. Instead of the ground providing a stable reaction force, the snow or sand gets displaced. This displacement means that less force is transmitted back to the foot.

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