Key Points

Pressure is defined as the force acting perpendicularly on a surface per unit area. The formula is $P = \frac{F}{A}$, where $P$ is pressure, $F$ is force, and $A$ is the area over which the force is distributed.

The SI unit of force is the newton (N) and the SI unit of area is the square meter ($m^2$). Therefore, the SI unit of pressure is newton per square meter ($N/m^2$), which is also called a Pascal (Pa).

For a constant force, pressure is inversely proportional to the area. A smaller area results in higher pressure ($P \propto \frac{1}{A}$), which is why a sharp knife cuts better than a blunt one.

If a force of $100$ N is applied over an area of $2$ $m^2$, the pressure exerted is calculated as $P = \frac{100 \text{ N}}{2 \text{ m}^2} = 50 \text{ N/m}^2$ or $50$ Pa.

The pressure exerted by a liquid at a certain point depends on the height (or depth) of the liquid column above that point. The greater the height of the liquid, the greater the pressure it exerts at the bottom.

Liquids exert pressure not only on the base of their container but also on the walls. At any given depth, a liquid exerts pressure equally in all directions.

The envelope of air surrounding the Earth, called the atmosphere, exerts pressure on all objects within it. This is known as atmospheric pressure. We are not crushed because the pressure inside our bodies balances the atmospheric pressure outside.

Air moves from a region of high pressure to a region of low pressure. This movement of air is what we call wind. The greater the pressure difference between two regions, the stronger the wind.

Uneven heating of the Earth causes pressure differences. Warm air is less dense, rises, and creates a low-pressure area, while cooler, denser air sinks, creating a high-pressure area.

High-speed winds are accompanied by a reduction in air pressure. This principle explains why weak roofs can be lifted and blown away during a storm, as the pressure below the roof becomes greater than the pressure above it.

Thunderstorms are formed by the rapid upward movement of warm, moist air. This leads to the formation of towering clouds, strong winds, heavy rain, and the electrical phenomena of lightning and thunder.

A cyclone is a large-scale, rotating storm system with a very low-pressure center (the eye). It forms over warm ocean waters when rising warm, moist air begins to spin due to the Earth's rotation.