Short Answer:

Pressure is defined as the force exerted by a fluid per unit area on a surface. It tells how much force is applied over a specific area and acts perpendicular to that surface. Pressure is a scalar quantity and is very important in fluid mechanics for analyzing forces in liquids and gases.

The SI unit of pressure is the Pascal (Pa), which is equal to one newton per square meter (N/m²). Other common units of pressure include bar, atmosphere (atm), millimeter of mercury (mmHg), and kilogram per square centimeter (kg/cm²).

Detailed Explanation :

Pressure and its Units

Pressure is a fundamental concept in fluid mechanics and physics. It expresses the effect of force acting on an area. In simple words, pressure is the amount of force applied by a fluid or object on a given surface. It helps to understand how fluids (liquids and gases) exert force on walls, containers, or objects submerged in them.

Mathematically, Pressure (P) is given by the formula:

Where,
= Pressure
= Force applied (in newtons)
= Area on which the force acts (in square meters)

From this equation, it is clear that pressure increases if the force increases or if the area decreases. This means that applying the same force over a smaller area produces greater pressure.

Explanation of Pressure

Pressure acts perpendicular to the surface of contact. For example, when air molecules collide with the walls of a container, they exert pressure on it. Similarly, when a fluid like water is stored in a tank, it exerts pressure on the tank walls and bottom due to its weight.

The study of pressure is important because it helps engineers design safe and efficient systems like hydraulic presses, pipelines, pumps, and pressure vessels. Pressure is also used to describe the behavior of gases in thermodynamics and the functioning of engines and turbines.

In fluids at rest, pressure acts equally in all directions — this is known as Pascal’s Law. According to this law, “Pressure applied to a confined fluid is transmitted equally and undiminished in all directions.” This principle is used in many hydraulic machines such as car brakes, lifts, and jacks.

Types of Pressure

There are several types of pressure used in engineering applications:

1. Atmospheric Pressure:
   It is the pressure exerted by the weight of air present in the atmosphere. At sea level, the average atmospheric pressure is approximately 1.013 × 10⁵ N/m² or 1 atmosphere (1 atm).
2. Gauge Pressure:
   It is the pressure measured above the atmospheric pressure. For example, a tire pressure gauge measures gauge pressure.
3. Absolute Pressure:
   Absolute pressure is measured with reference to a perfect vacuum. It is the sum of atmospheric pressure and gauge pressure.

1. Vacuum Pressure:
   When the pressure in a system is below atmospheric pressure, it is called vacuum pressure. It is commonly found in suction pumps or vacuum systems.

Units of Pressure

The SI unit of pressure is the Pascal (Pa). It is defined as:

This means that when a force of one newton acts on an area of one square meter, the pressure produced is one pascal.

Other common units of pressure include:

• Bar: 1 bar = 10⁵ Pa
• Atmosphere (atm): 1 atm = 1.013 × 10⁵ Pa
• Millimeter of Mercury (mmHg or Torr): 1 mmHg = 133.3 Pa
• Kilogram per square centimeter (kg/cm²): 1 kg/cm² = 9.81 × 10⁴ Pa

These units are used depending on the application. For example, atmospheric pressure is often expressed in bars or mmHg, while hydraulic systems use kg/cm² or Pascal.

Practical Examples of Pressure

• Hydraulic Systems: Pressure is used to lift heavy loads using a small force in devices like hydraulic jacks and brakes.
• Pneumatic Systems: Air pressure is used in tools and machinery to perform work efficiently.
• Weather Studies: Atmospheric pressure measurements help in predicting weather patterns.
• Fluid Flow: Pressure difference causes fluids to flow through pipes and channels.

Importance of Pressure in Engineering

Pressure plays a major role in mechanical and civil engineering. It helps in:

• Designing containers that can handle internal and external fluid pressure.
• Understanding how pumps, compressors, and turbines work.
• Ensuring safety in boilers and gas cylinders.
• Calculating the forces acting on submerged bodies like ships or submarines.

Thus, pressure is a key parameter in almost every system involving fluids or gases.

Conclusion

Pressure is defined as the force per unit area acting perpendicular to a surface. It determines how strongly a fluid or object exerts force on its surroundings. The SI unit of pressure is Pascal (Pa), and other units include bar, atmosphere, and mmHg. Pressure is essential in engineering for designing and analyzing systems like hydraulic machines, pumps, and pipelines. Understanding pressure helps engineers ensure safe, efficient, and reliable operation of mechanical systems.