#pressure #physics #textbook #calculatingpressure

Pg:- 93,94,95,96

Ch:- 5

Pressure is the force exerted per unit area on a surface. It is a scalar quantity

Definition and Formula

The pressure (P) is mathematically defined as:

P= FA

Where:

• P = pressure

• F = force applied perpendicular to the surface

• A = area over which the force is distributed

The SI unit of pressure is the pascal (Pa), which is equivalent to 1 N/m² (one newton per square meter).

Understanding Pressure

• Force (F): Pressure is the result of a force applied to an area. The force must be perpendicular to the surface for pressure to be calculated this way.

• Area (A): The same force applied over a larger area produces lower pressure, while the same force on a smaller area produces higher pressure.

For example:

• If you apply the same force on a sharp needle and on a flat block, the needle will exert a much higher pressure due to its smaller area, which is why it can pierce surfaces.

Units of Pressure

Pressure can be expressed in various units:

• Pascals (Pa): 1 Pa = 1 N/m²

• Atmospheres (atm): 1 atm ≈ 101,325 Pa

• Bar: 1 bar = 100,000 Pa

• Millimeters of mercury (mmHg): 1 atm = 760 mmHg

• Pounds per square inch (psi): 1 psi ≈ 6,894.76 Pa

Calculating Pressure

Here’s how you calculate pressure in different scenarios:

1. Simple Surface Pressure: Suppose a force of 50 N is applied to an area of 10 m². The pressure would be:

   
   

   P= FA = 50 N/10 m2 = 5 Pa

   
   

2. Pressure in a Fluid: In fluids, pressure increases with depth due to the weight of the fluid above. The pressure at a depth h in a fluid with density ρ\rhoρ, under gravitational acceleration g, is given by:

   P= P0 + ρgh

   Where:

   • P​ is the pressure at the surface (e.g., atmospheric pressure),

   • ρrho is the density of the fluid,

   • g is the acceleration due to gravity,

   • h is the depth within the fluid.

3. Atmospheric Pressure: Atmospheric pressure is the weight of the air above a certain point. At sea level, this is typically about 101,325 Pa or 1 atm.

• Pressure is a measure of how much force is applied over a certain area.

• It is calculated as the ratio of force to area.

• Pressure in fluids varies with depth due to the weight of the fluid above.

• Atmospheric pressure is a standard measurement used in many calculations and affects pressure in fluids at open-air interfaces.