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Written here are net forces acting on a body. But I am having difficulty in understand them after reading from textbook and online material.

In the book, we have been introduced to thrust.

It clearly says that pressure exerted by a body on the surface = weight of the body.

Then, why is it not that $mg$ is nothing but $P_1A$ and $P_2A$?

Can we also say that it is $F = ma$ expression (the first equation as a whole) where $a = 0$?

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  • $\begingroup$ Thrust has the units of force not pressure. Please recheck $\endgroup$
    – shahrOZe
    Dec 26 '20 at 6:53
  • $\begingroup$ @shahrozeshahab Please recheck my post.I $\endgroup$
    – srijan Sri
    Dec 26 '20 at 6:58
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    $\begingroup$ Weight of a body is equal to the difference of thrust P1A and P2A ( thrust acting on the top and bottom respectively) only if its in equilibrium $\endgroup$
    – shahrOZe
    Dec 26 '20 at 7:02
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It clearly says that pressure exerted by a body on the surface = weight of the body.

It is simply impossible — their units are different: $\left[N \over m^2\right]$ vs. $[N]$.

Your book says something other - thrust, not pressure.

The picture is about forces and their difference. There are

  • 2 forces in the top-to-down direction (the gravitational force and the force caused by the water pressure)
  • 1 force in the down-to-top (the force caused by the water pressure).

So the first two forces are added together and the last force is subtracted from their sum.

The resulting force must be a zero force, because the cylinder is not moving.

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  • $\begingroup$ Ok.I understood.I have also put the photo of what was there exactly in my book.I got very confused with that.Thank you for helping. $\endgroup$
    – srijan Sri
    Dec 26 '20 at 6:53
  • $\begingroup$ You're welcome. What should I do when someone answers my question? $\endgroup$
    – MarianD
    Dec 26 '20 at 6:59
  • $\begingroup$ Just one thing.how is it possible that my book has written wrong statement ?.That is a very big thing right $\endgroup$
    – srijan Sri
    Dec 26 '20 at 7:02
  • $\begingroup$ No, the statement in your book is correct — see my (edited answer), it is about thrust, not about pressure. $\endgroup$
    – MarianD
    Dec 26 '20 at 7:05
  • $\begingroup$ Oh.Ok thank you. $\endgroup$
    – srijan Sri
    Dec 26 '20 at 7:06

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