Chapter: 4.2

Hydrostatics Pressure

First, let’s review what the pressure is. In physics, the pressure is defined as a force acting perpendicular to a unit area, or as a tension inside a closed fluid. Next, we will learn what hydrostatic pressure is.

HYDROSTATIC PRESSURE

Hydrostatic pressure is the pressure in a stationary liquid due to its own weight. In incompressible liquids, the pressure increases in direct proportion to the depth.

The hydrostatic pressure depends only on the height of the liquid column and does not depend on the shape of the container.

This seemingly contradictory fact is known as the hydrostatic paradox.

Hydrostatic pressure also depends on the density of the liquid.

Example 1

Figures show that the hydrostatic pressure increases with the depth of coloured water.

The hydrostatic pressure is higher.
The hydrostatic pressure is lower.

Example 2

In the animation below, pay attention to the height of the liquid level in the different shaped containers.

What happens to the water level in all the connected glass tubes?

We see that the water level in all connected glass tubes of different shapes is the same.

How is this finding related to hydrostatic pressure?

The pressure in a given fluid is always the same at the same depth and does not depend on the shape of the container in which the fluid is held. The fluid is distributed at the same level in all parts of such a connected container. This shows that the pressure at the bottom of each container is the same. This fact is known as the hydrostatic paradox.