Theory:

Before we get into the definition of pressure, let us look at the following activity.
Consider you have two nails, one with a sharp edge and another one with a blunt edge; which one will penetrate the wood easily?
  
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Iron nail with a sharp edge
 
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Iron nail with a blunt edge
 
Iron nail with a sharp edge would penetrate the wood easily. The reason for this is pressure. Let us discuss about pressure in a detailed manner.
  
Pressure:
The pressure is the quantity with which can measure how much force is exerted on a body. It can also be defined as the amount of force applied perpendicularly on a unit square meter area.
Pressure=ForceArea
The unit of pressure is N/m2.
The area in the denominator is inversely proportional to the force. So, the smaller the area, the larger the pressure, whereas the larger the area, the less the pressure acts. Therefore, the area and force decide the pressure acting on the surface. This is why the nail with a sharper edge penetrates the wood easily than the nail with a blunt edge.
 
Look at the following example
A knife has a tiny and sharp edge to exert more pressure on the opposite object's smaller area to get the maximum effect from it.
 
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Knife with smaller area