0

I was going through the derivation of a mathematical equation for the upthrust exerted on a body which is given in my book.

It says that the downward pressure exerted on the upper surface is less than the upward pressure on the lower surface. Thus, there is a net pressure acting in the upward direction and therefore, a net upward force. The lateral pressure gets counterbalanced.

I am able to understand that the pressure in the downward direction is due to gravity and the lateral pressure is due to the fluid's tendency to flow. However, I am not able to understand how the fluid exerts pressure in upward direction.

I have worked on the problem and arrived at two different explanation:-

  1. The pressure inside a fluid is due to the collision of the particles. Since, collision is random, pressure can be considered to be equal in all directions at the same horizontal level.

  2. The fluid exerts a pressure and thus, a force on the bottom of the container and the reaction of this force exerts upward pressure.

Question:-

How does a static fluid exert pressure in the upward direction? Which explanation of mine is correct?

  • I'd start with https://physics.stackexchange.com/questions/669362/why-does-a-fluid-push-upward-on-a-body-fully-or-partially-submerged-in-it?rq=1 – BowlOfRed Aug 21 '23 at 17:29

2 Answers2

0

At any given point a perfect or ideal fluid exerts the same pressure in all directions. This is part of the definition of an ideal fluid, and the ideal fluid model is a good approximation to many real-world fluids. The increase of pressure with depth is due to gravity.

gandalf61
  • 52,505
0

Its not only a definition, but I can explain it. Imagine a cube of water 10cm10cm10cm it has the mass 1kg so 10N weight , 10 cm below the surface, on top you have a pressure of 10N/100cm^2, so add the wight and at teh bottom of the cube you have a force of 20N but this cube does not sink as you know , so there must be a force up of 20 N so a pressure of 20N/100cm^2.

trula
  • 6,146