Hydrostatic Pressure

## Question:

An object placed underwater experiences hydrostatic pressure from all direction. I think the hydrostatic pressure on top of the object comes from the weight of water above it, but where do the lateral hydrostatic pressure comes from? It is from the movement of water particles? If so, then will the hydrostatic pressure of water greater at a higher temperature then at a lower temperature?

All pressure from a fluid is transmitted by the collisions between the fluid particles and a submerged, or partially submerged object. The hydrostatic pressure at any depth is the pressure resulting from the column of water above that depth. Because the fluid cannot support any significant shear force the pressure is directed in all directions.

Imagine a box filled with marbles (glass spheres about 1 cm in diameter). If you push down with your hand on the marbles, the force you provide does not move all marbles in the downward direction. Some will move sideways and some will move upward. This is because the marbles being spheres only contact another marble at a single point. That single point of contact does not provide a rigid connection between marbles. That contact point is free to move anywhere as long as the distance between marble centers remains 1 diameter. The same phenomena is taking place in the fluid, transmitting pressure in all directions.

The hydrostatic pressure will depend on the temperature only to the extent that the column of water above the object has decreased density with increased temperature.