# concept of pressure

i am at a stage where i really need to have an in depth intuition about properties governing nature; and when i look at force, i can picture its effects it in my mind(change in movement,deformation) by replacing objects with force vectors and theoretically analyse them, but when it comes to pressure, i understand the definition but can not get an intuitive knowledge about pressure,especially in fluids. so i came up with my own theoretical experiments which might help me get an intuition about it, and i need a second opinion on the possible answers or further methods which might help me get a more comprehensive understanding of pressure.So,here are the questions:-

1. Assume there is a $1m$ by $1m$ square flat plate. And I divide the area into $50$ by $50$ equal partitions. Then I apply point forces on every midpoint of the partitions all pointing downwards perpendicularly with magnitude $1N$, what is the pressure exerted on this $1m$ by $1m$ square flat plate? TRIAL: The answer is: $\frac{50 \times50\times1N}{1m\times1m}=2500Pa$.Initially i was tempted to say $1Pa$,but i later understood the definition of pressure and why it is a scalar quantity because it describes the SUM of all forces(perpendicular ones) present in a unit area.

2. I have taken strength of materials course and worked with stress and strain.There is a concept about yield or ultimate strength which i totally understand, and there are corresponding stess values(yield or ultimate strength) to materials, for example, $A36$ steel has yield strength of $250Mpa$.when i say this statement, am i including atmospheric pressure? in other words, if i measure the yield strength in space, where there is negligible pressure is the yield strength of $A36$ steel a different value than the one i measured here in earth,maybe($250.1Mpa$)?

3. While i am sitting down, I looked at the palm of my hand. and i measured a reasonable $4cm\times4cm$ square and i said to my self that around this sqaure area there is an air pressure of $0.1Mpa$,so a total force of $0.1M\times0.04\times0.04=160N$.To make things simpler i assumed gravity is $10\frac{m}{s^{2}}$.so it seems i am always holding a $16kg$ object.And if i am lying flat down and simply take a $15cm\times15cm$ square, a $225kg$ object is crushing my gut, so if i go to a theoretical planet with no atmosphere and gravity of $10\frac{m}{s^{2}}$, will my body withstand if a $225kg$ object is sitting on my body?

• For item 3, if, on the theoretical planet, you would need to apply a normal pressure of 0.1 MPa over your whole body if you wanted to simulate the effect of earth's atmosphere. If you only did it over a 15x15 square, you skin would be bulging out over the rest of your body. And there would be a high stress on the edges of the square. – Chet Miller Oct 26 '17 at 16:21

1) You are right. You can even confirm this my measuring pressure exerted on each of those partitions. 1/50th of a meter is 2 cm. $2*2=4cm^2$.
$1N/4cm^2=2500 Pa$