Answer:
Both the cases deal with the principle of pressure due to force acting on an area.
Explanation:
When a stone is place between a pile of book and our head when we carry it then the area subjected to the force decreases while the magnitude of the force remains same and therefore the pressure on our head increases.
As we know that pressure is force per unit area is called pressure.
Mathematically:
It is easy to cut our skin with an edge of a paper because our skin is relatively softer than the edge of a paper and the edge of a paper is thin which applies more pressure due to less area of contact with our skin.