Question

A chef while cooking cuts his hand with a sharp edged knife, but to his surprise his hand did not cut with a spoon even on the application of a greater force. Why was it cut from a knife for a smaller force?

Answer 1

In order to answer the question you must be clear about the point that pressure and force are interrelated. There is a basic relation between both and using that only we can achieve the solution. Whenever force is applied it induces pressure in the body on which the force is applied. Pressure is measured only on the perpendicularly applied forces.

Complete step by step solution:
Pressure is defined as the force acted perpendicularly on the object’s surface in a unit area (i.e. perpendicular force acting on a unit surface area). Numerically it is given as
$P = \dfrac{F}{A}$
Where,
$P = {\text{Pressure }}$
$F = {\text{Force applied}}$
$A = {\text{Area}}$
From the equation it is clearly evident the relation between area and force and pressure. Pressure is inversely related to area i.e. larger the area lesser will be the produced force.
This relation is evident that being a knife but having a sharp edge reduces the area on which the force is to apply. Being a sharp edge it provides a very less contact area on which force is applied by knife. Due to less contact area the pressure produced by the knife is much larger.
And on the other hand it is clear that a spoon being of large area itself reduces the pressure of force applied by it. So in case of the same amount of force applied, the substance having lesser area will have high pressure. Hence, the knife cuts open the skin while the spoon isn’t capable of doing so.
Note:
Pressure and force relation has proven its application in several fields like the area of hammer is made large and that of screw or pin or nails are made small so that on application of any amount force by hammer the sharp edged nails can easily pass the barrier by producing large pressure from that force.