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If we put an object on a table and this object has a uniform distribution of mass, then the force exerted by the object on the table would be uniformly distributed in case the area of contact of the object is equal or larger than to that of table , on the other hand the force would not be uniformly distributed in case the area of contact of object is smaller than the area of table . Am I thinking right?

Now how could we measure the pressure of a force that's not uniformly distributed over an area ?? Because calculating the pressure in case the force was uniformly distributed is easy ( pressure everywhere is equal to average pressure : total force / whole area)

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  • $\begingroup$ -1 Not clear. Do you want to calculate average pressure? If pressure varies over the surface then it has many values, like temperature. You have to specify at what point you are measuring it. $\endgroup$ Commented Mar 1, 2018 at 16:02
  • $\begingroup$ Possible duplicate of Define Pressure at A point. Why is it a Scalar? $\endgroup$ Commented Mar 1, 2018 at 18:02

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You must use a smaller area to measure a force exerted over a smaller area. If your pressure-gauge has a certain area $A_{tot}$ and you calculated pressure by measuring $F_{tot}$, the net force exerted on the whole area, then you calculate pressure by $P_{avg} = \frac{F_{tot}}{A_{tot}}$. As you've identified in the OP, this type of pressure measurement can only calculate the average force averaged over the whole area $A_{tot}$. You must have a smaller area to determine finer resolution pressure information.

More generally, any detector averages whatever physical quantity it is measuring over the detector size. If you want higher resolution you must have a smaller detector. One can make an analogy between pixels in a camera or pixels in your computer screen. If you have two identical cameras but one has smaller pixels then if they take the same picture the one with smaller pixels will give you more details information, whereas on the one with bigger pixels some of the finer details will be blurred out and averaged between pixels.

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