Thread: Pressure on a lateral side of a tank

Hello,world
I already started this thread on this page Pressure on a lateral side of a tank - Page 2
but the discission stopped and i'm still confused so I hope you spend some time reading the thread

Or to put it another way,

Total force on lateral surface = (area of surface) * (average pressure on the surface)

... and the average pressure is the pressure half way up the side.

My question:

Acoording to your equation:the pressure applied at any point on the lateral surface equals to the average pressure.and by multiplying pressure-force per unit area-times the whole area,thus we get the total force applied on the lateral wall.
and that's not true beacuse the pressure varies along the lateral surface
Could you realise my problem?
Thanks

and this is my post answering the question I asked :

Well,okay,may be you mean that force is still the same whatever the way we distribute it.

Is that true?
read the latest posts in the thread above and tell me If I'm on the right way or not.
may be my main problem is that i can't really differniate between force and pressure

Thanks in advance

I don't know what you mean by "Well,okay,may be you mean that force is still the same whatever the way we distribute it." You might be getting the idea, or maybe not.

The total force is the sum of all the forces. Near top of the tank one square millimeter will exert a certain force proportional to the pressure. At the bottom of the tank, a square millimeter will exert more force because the pressure is higher. If you add up the force on all the square millimeters, you get the total force. If you divide the total force by the number of square millimeters, you get the average force per square millimeter, or average pressure. Do you understand the concept of an average?

Originally Posted by Misr

According to your equation:the pressure applied at any point on the lateral surface equals to the average pressure.

No, this is not what is being said. The pressure applied on the lateral surface increases linearly with depth in the liquid, but because it is linear (for an incompressible fluid) you can take the average value between top and bottom of the tank and multiply it by the area of the lateral surface to get the total force.

Taking the average is just a mathematical procedure that works because the pressure varies linearly.