Talha's Physics Academy
Forces and Matter - Pressure and Fluid Pressure
Define Pressure and its units.
Pressure
"The force applied normal (perpendicular) per unit area is called pressure."
Mathematically, pressure ($P$) is expressed as:
$P = \frac{F}{A}$
Where:
- $F$ = Applied Force
- $A$ = Surface Area
SI Unit of Pressure
Since force is measured in newtons ($\text{N}$) and area in square meters ($\text{m}^2$), the SI unit of pressure is newton per square meter ($\text{N/m}^2$), which is also known as the Pascal ($\text{Pa}$):
$1\text{ Pa} = 1\text{ N}\cdot\text{m}^{-2}$
Describe pressure in fluids and factors affecting pressure.
Pressure in Fluids
A fluid is a collection of molecules that are randomly arranged and held together by weak cohesive forces and by forces exerted by the walls of a container. Both liquids and gases are fluids. The pressure exerted by fluids is known as fluid pressure.
"Fluid pressure acts in all directions because the molecules of fluids move around freely in all directions, causing pressure on every surface they collide with."
Example: A swimmer in a swimming pool experiences pressure from water pushing against them from all sides.
Factors Affecting Fluid Pressure
The pressure $P$ at a depth $h$ in a fluid depends upon depth, fluid density, and acceleration due to gravity:
- Depth ($h$): Pressure is directly proportional to depth. The deeper one dives into water, the greater the pressure (e.g., twice the depth means twice the pressure).
- Density ($\rho$): Pressure is directly proportional to the density of the fluid. If a liquid is five times denser than water, the hydrostatic pressure at any given depth will be five times greater.
- Acceleration due to Gravity ($g$): The weight of the fluid column above depends on local gravity.
Figure: Difference of Pressure due to Height.
Mathematically, liquid pressure is given by the formula:
$P = \text{depth} \times \text{density} \times \text{acceleration due to gravity} \implies P = \rho g h$
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