# Pressure

### Table of Contents

## Introduction to Pressure

In physics, **Pressure** is the **force per unit area** applied perpendicular to the surface of an object or fluid.

**Formula**: $P=AF $

**P**: Pressure**F**: Force applied perpendicular to the surface**A**: Area over which the force is applied

**Units of Pressure**

**SI System**: Pressure is measured in**Pascals (Pa)**, where 1 Pascal is equal to 1 Newton per square meter (1 Pa = 1 N/m²).**CGS System**: Pressure is measured in**Barye (Ba)**, where 1 Barye is equal to 1 dyne per square centimeter.

**Atmospheric Pressure**

- Atmospheric pressure is the
**constant force exerted by the Earth’s atmosphere**on its surface. **Role in Weather Patterns**: Influences**weather patterns**and**climate changes**.**Role in Altitude Variations**: Atmospheric pressure decreases with**increasing altitude**, affecting**airplane flights**and**mountain climbing**.

## Types of Pressure

**Fluid Pressure**

**Definition**: Fluid pressure is the **transmission of force in fluids** (liquids and gases) due to their inability to resist deformation.

**Examples**:

**Hydraulic Systems**: Use fluid pressure to transmit force.**Pressure Cookers**: Increase cooking efficiency by raising the boiling point of water.**Buoyancy in Liquids**: Objects float or sink based on fluid pressure exerted on them.

**Applications in Exams**:

**Hydrostatics**: Study of fluids at rest.**Fluid Mechanics**: Applications in engineering, including designing pumps, pipes, and turbines.

**Gas Pressure**

**Definition**: Gas pressure is based on the **kinetic theory of gases**, where gas particles move randomly and collide with each other and the container walls.

**Examples**:

**Barometers**: Measure atmospheric pressure.**Inflating Balloons**: Air pressure inside the balloon is higher than the external pressure.**Working of Car Engines**: Combustion process relies on gas pressure for engine operation.

**Applications in Exams**:

**Thermodynamics**: Study of heat and energy transfer, relevant in both engineering and medical fields.

**Atmospheric Pressure**

**Definition**: Atmospheric pressure is the **weight of the air column** above a given point on Earth’s surface.

**Examples**:

**Weather Forecasting**: Changes in atmospheric pressure indicate weather changes.**Working of Vacuum Cleaners**: Suction is created due to the difference in atmospheric pressure.**Human Body and Pressure Changes**: Effects of pressure changes during flights, scuba diving, etc.

**Applications in Exams**:

**Atmospheric Science**: Study of Earth’s atmosphere, relevant in geography exams.**Physiology**: Study of human body functions, including the effects of pressure, relevant in medical exams.

## Factors Affecting Pressure

**Depth**

**Increase in Pressure**: Pressure**increases**with**depth**in both liquids and gases.**Explanation**: As depth increases, the weight of the overlying fluid creates additional pressure due to the column of fluid above.

**Density**

**Relationship**: Higher**density**of a fluid leads to**greater pressure**exerted by it.**Explanation**: Denser fluids have more mass in a given volume, resulting in increased gravitational force and, consequently, higher pressure.

**Gravity**

**Influence on Pressure**:**Gravitational force**significantly affects pressure, especially in liquids.**Explanation**: Gravity causes the weight of the fluid column to exert pressure on the underlying surfaces, contributing to the overall pressure experienced.

## Measurement of Pressure

**Different Units of Pressure**

**SI Units**: Pressure is primarily measured in**Pascals (Pa)**.**Non-SI Units**: Other common units include**atmospheres (atm)**,**millimeters of mercury (mmHg)**, and**pounds per square inch (psi)**.**Conversions**:- 1 atm = 101,325 Pa
- 1 mmHg = 133.322 Pa
- 1 psi = 6,894.76 Pa

**A. Manometric Instruments**

**Simple Manometer**:

**Principle**: It operates on the principle of**Balanced Pressure**.**Working**: Measures pressure by comparing the liquid levels in two connected columns, indicating the pressure difference.

**Applications**:

**Measuring Pressure Differences**: Used in various applications such as**blood pressure measurement**in medical settings.

**B. Barometers**

**Types of Barometers**:

**Mercury Barometer**: Uses a column of mercury to measure atmospheric pressure.**Aneroid Barometer**: Utilizes a flexible metal box to measure pressure changes.

**Working Principles**:

**Mercury Barometer**: Atmospheric pressure pushes mercury up a tube, with height indicating pressure.**Aneroid Barometer**: Pressure changes cause the metal box to expand or contract, which is measured and displayed.

**Applications**:

**Weather Forecasting**: Helps in predicting**weather changes**based on atmospheric pressure.**Altitude Measurement**: Used to determine**altitude variations**in aviation and mountain climbing.

## Applications of Pressure

**Hydraulic Systems**

**Importance**: Pressure plays a**crucial role**in the operation of**hydraulic machinery**and equipment.**Function**: Hydraulic systems use**fluid pressure**to generate, control, and transmit power.

**Weather Phenomena**

**Predicting Weather**: Atmospheric pressure variations help in**predicting weather conditions**.**Weather Patterns**: High and low-pressure systems influence**rainfall**,**wind patterns**, and**temperature changes**.

**Medical Applications**

**Blood Pressure Monitors**: Measure**blood pressure**using pressure sensors to detect the force of blood against artery walls.**Ventilators**: Control**air pressure**to assist patients with breathing, especially in critical conditions.

## Conclusion

- In conclusion, pressure, a fundamental concept defined as force per unit area, permeates every aspect of our world, from the microscopic (gas molecules) to the macroscopic (atmospheric effects).
- We explored various pressure types – fluid, gas, and atmospheric – and their diverse applications across disciplines like physics, engineering, and medicine.
- From the intricate workings of hydraulic machines to the delicate balance within the human body, pressure plays a crucial role in everyday life and scientific advancements.

### FAQ’s

Imagine pushing down on a ball of clay. The amount of **squish** you create, considering both the force you apply and the area it’s spread over, is pressure! In scientific terms, it’s the **force applied perpendicular to a surface divided by the area over which that force is distributed.**

The SI unit of pressure is the **Pascal (Pa)**. Think of one Pascal as the pressure exerted by a tiny force pushing on an area about the size of your fingernail.

Pressure is calculated using the formula: **P = F / A**, where:

- P is pressure (in Pascals)
- F is the force applied (in Newtons)
- A is the area over which the force is applied (in square meters)

The most common unit for pressure is the **Pascal (Pa)**, as mentioned above. However, there are other units used in different contexts.

Yes! Another unit you might encounter is **dynes per square centimeter (dyn/cm²)**, which belongs to the CGS system.

### Related Links

### MCQ’s

**1.** **What is pressure?**

a) The force applied perpendicular to the surface

b) The force applied parallel to the surface

c) The force applied in any direction

d) The force applied diagonally

**Answer:** a) The force applied perpendicular to the surface

**2.** **Which formula represents pressure?**

a) $P=VF $

b) $P=FA $

c) $P=AF $

d) $P=F+A$

**Answer:** c) $P=AF $

**3.** **What does ‘P’ stand for in the pressure formula?**

a) Volume

b) Force

c) Pressure

d) Area

**Answer:** c) Pressure

**4.** **In the SI system, pressure is measured in:**

a) Joules

b) Pascals

c) Newtons

d) Watts

**Answer:** b) Pascals

**5.** **What is the unit of pressure in the CGS system?**

a) Newton

b) Pascal

c) Dyne

d) Watt

**Answer:** c) Dyne

**6.** **Atmospheric pressure is due to:**

a) Water pressure

b) Air pressure

c) Gravitational force

d) Magnetic force

**Answer:** b) Air pressure

**7.** **Atmospheric pressure decreases with:**

a) Increasing depth

b) Increasing temperature

c) Increasing altitude

d) Increasing density

**Answer:** c) Increasing altitude

**8.** **What is the formula to calculate pressure?**

a) $P=F×A$

b) $P=F−A$

c) $P=F÷A$

d) $P=F+A$

**Answer:** c) $P=AF $

**9.** **Which of the following is NOT a unit of pressure?**

a) Joule

b) Pascal

c) Bar

d) Atmosphere

**Answer:** a) Joule

**10.** **Pressure increases with:**

a) Increasing area

b) Decreasing force

c) Increasing depth

d) Decreasing density

**Answer:** c) Increasing depth

**11.** **What is the unit of pressure in the CGS system?**

a) Newton

b) Pascal

c) Dyne

d) Watt

**Answer:** c) Dyne

**12.** **What causes soda cans to pop when opened?**

a) Low pressure inside the can

b) High pressure inside the can

c) Equal pressure inside and outside the can

d) Magnetic force

**Answer:** b) High pressure inside the can

**13.** **Atmospheric pressure is maximum at:**

a) Sea level

b) Mountain peak

c) Deep ocean

d) Desert

**Answer:** a) Sea level

**14.** **The principle behind the functioning of hydraulic systems is:**

a) Boyle’s Law

b) Pascal’s Principle

c) Archimedes’ Principle

d) Newton’s Third Law

**Answer:** b) Pascal’s Principle

**15.** **Pressure and volume are related by:**

a) Boyle’s Law

b) Archimedes’ Principle

c) Pascal’s Principle

d) Newton’s Law

**Answer:** a) Boyle’s Law

**16.** **The force applied on an area of 5 m² to produce a pressure of 50 Pa is:**

a) 10 N

b) 250 N

c) 100 N

d) 5 N

**Answer:** b) 250 N

**17.** **Pressure increases with:**

a) Increasing area

b) Decreasing force

c) Increasing depth

d) Decreasing density

**Answer:** c) Increasing depth

**18.** **Atmospheric pressure is due to:**

a) Water pressure

b) Air pressure

c) Gravitational force

d) Magnetic force

**Answer:** b) Air pressure

**19.** **Pressure and volume are related by:**

a) Boyle’s Law

b) Archimedes’ Principle

c) Pascal’s Principle

d) Newton’s Law

**Answer:** a) Boyle’s Law

**20.** **The force applied perpendicular to a surface is 120 N. If the area is 15 m², what is the pressure?**

a) 8 Pa

b) 135 Pa

c) 105 Pa

d) 110 Pa

**Answer:** c) 105 Pa