Pressure variation with location - 1.8 | 3. Basics of fluid mechanics - I (Contd.) | Hydraulic Engineering - Vol 1
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Pressure Variation with Depth

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Teacher
Teacher

Today, we will explore how pressure in a fluid changes with depth. Can anyone tell me why we experience increased pressure the deeper we go underwater?

Student 1
Student 1

It’s because there's more water above pushing down on us, right?

Teacher
Teacher

Exactly! The weight of the water above creates pressure. To help remember this, think of it as WAD: Weight Above Depth. Remember, the deeper you go, the more water is pressing down.

Student 2
Student 2

So, if a submarine goes deeper, it has to deal with more pressure?

Teacher
Teacher

Correct, especially when considering its crush depth! The deeper it goes, the higher the water pressure, which is why submarines have specific limits on how deep they can dive.

Student 3
Student 3

What about how pressure is exerted? Isn’t it also perpendicular to surfaces?

Teacher
Teacher

Yes! Pressure acts perpendicularly on surfaces due to its nature. This is very important in designing various hydraulic structures.

Student 4
Student 4

Can we discuss real-world applications of this concept, like in dams?

Teacher
Teacher

Certainly! Understanding pressure at different depths is crucial in dam design to ensure they can withstand the weight of the stored water. Let's summarize what we've learned: pressure increases with depth, is perpendicular to surfaces, and has significant implications for engineering!

Applications in Hydraulic Engineering

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Teacher
Teacher

Let’s delve deeper into applications of pressure variation. Can anyone think of an example where this principle is crucial?

Student 1
Student 1

I remember you mentioned the Bhakra Nangal Dam in class!

Teacher
Teacher

That's right! The pressure on different parts of the dam’s structure varies with depth. This affects its stability and design. Recall our acronym WAD — it helps us remember the relationship between weight, area, and depth.

Student 2
Student 2

What happens when there’s a change in pressure direction, like with Pascal's Law?

Teacher
Teacher

Great question! Pascal's Law states that pressure applied to an enclosed fluid is transmitted undiminished throughout the fluid. This leads to many applications, like hydraulic lifts and brakes.

Student 3
Student 3

How can we see this in a simple experiment?

Teacher
Teacher

You could fill a container with water and use different holes to observe varying water jet heights. Remember, with greater pressure, the water shoots further! Let’s summarize: pressure varies with depth, influences hydraulic design, and is governed by Pascal’s Law.

Understanding Fluid Statics

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Teacher
Teacher

As we continue, let's discuss fluid statics. What do we know about forces acting in still fluids?

Student 1
Student 1

Out there is no relative motion, which means shear stress is zero!

Teacher
Teacher

Exactly! This means only pressure forces are at play. To remember this, think about the phrase 'No Shear, Just Pressure.' Pressure impacts all surrounding surfaces and varies with depth.

Student 2
Student 2

Are there practical tools or equations to measure this pressure?

Teacher
Teacher

Yes! Barometers are used to measure atmospheric pressure, which is crucial for setting reference points in fluid studies. Who can summarize what we learned about fluid statics?

Student 3
Student 3

Only pressure acts in still fluids, we explored barometers, and pressure increases with depth.

Teacher
Teacher

Perfect summary! Understanding these concepts is fundamental for fluid mechanics. Great work today!

Introduction & Overview

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Quick Overview

This section discusses how pressure varies with depth in a fluid and the implications for engineering applications, particularly in hydraulic systems.

Standard

The section explains the relationship between pressure and depth in a liquid, emphasizing that pressure increases with depth due to the weight of the fluid above. It provides insights into practical applications, such as the design of dams and submarines, while highlighting fundamental principles of fluid mechanics.

Detailed

In hydraulic engineering, understanding the variation of pressure with location is crucial. As demonstrated, pressure in a fluid increases with depth, a phenomenon familiar to those who have experienced scuba diving. This increase is due to the weight of the fluid above a given point, which exerts force on the fluids below, leading to higher pressure. This principle is essential in applications like submarine operation, dam design, and determining forces on submerged surfaces. Furthermore, the section discusses Pascal's Law and the independence of pressure from direction, stressing that pressure only depends on the depth of the fluid column above a point. This concept is vital for calculating forces on submerged surfaces and plays a significant role in ensuring the structural integrity of engineering designs such as dams.

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Introduction to Pressure Variation

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One of the most important question is the variation of pressure with depth in a liquid. How does the pressure vary? So, to be able to, you know, give a real feel has anyone of you have done scuba diving that you will observe that the pressure increases as then you go down. So, compared to if you are at the upper surface, than at the lower surface, at the lower depths the pressure will increase. The increasing water pressure with depth limits how deep a submarine can go. These are the 2 classical example of the variation of pressure with depth and a liquid.

Detailed Explanation

This section introduces the concept of pressure variation in liquids, particularly how pressure increases with depth. As you dive into water, the weight of the water above you increases due to gravity, resulting in higher pressure at lower depths. This principle is crucial for understanding phenomena in both natural and engineered systems involving fluids.

Examples & Analogies

Think of a soda can. When you shake it, the pressure builds up inside due to the liquid being agitated and the gas trying to escape. Similarly, in deep waters, the pressure builds up due to the water weight above. That's why submarines have a crush depth—beyond that, the pressure is too great for the structure to withstand, just like a soda can would burst if shaken and opened too quickly.

Why Does Pressure Increase with Depth?

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So, now the important question is why P increases with depth. This is a volume of liquid. As you can see there are some layers on it. So, this is one layer, right? This is one layer. So, this means, this particular layer that have to support the entire liquid that is above this layer and the same is for this layer. So, this means, this layer will have to support this much plus this much.

Detailed Explanation

Pressure increases with depth due to the cumulative weight of the liquid above. Each layer of liquid exerts pressure not only from its weight but also from all the layers above it. For example, if you imagine several blocks stacked on top of each other, the block on the bottom must support the weight of all the blocks above it. This cumulative effect results in increased pressure at greater depths.

Examples & Analogies

Consider walking on a pile of snow. The snow at the bottom has to support all the snow above it. The deeper you go into the snowdrift, the more pressure is exerted on the lower layers. Similarly, the further down you go in a body of water, the more water presses down on you, increasing the pressure as you go deeper.

Characteristics of Pressure

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One of the other important feature of pressure is that pressure is always perpendicular to the surface. And the pressure does depend only on depth we are going to see that will do some basic derivation later in this lecture, where you will see that the dependence of pressure is only on depth is very important to note.

Detailed Explanation

Pressure acts equally in all directions and is always perpendicular to the surface it acts upon. This characteristic of pressure means that regardless of the specific orientation of that surface, the pressure exerted is the same, as long as depth remains constant. This relationship is crucial for designing structures subjected to fluid pressure.

Examples & Analogies

Imagine putting a balloon at the bottom of a pool. Whether the balloon is sitting flat on the pool floor or slanted at an angle, the pressure from the water is always perpendicular to its surface, pushing in equally from all sides. This property allows engineers to predict how structures, like dam walls, will behave under pressure.

Practical Applications of Pressure Concepts

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Now, some definitions and applications, in fluid statics as we have seen there is no relative motion between the adjacent fluid layers, therefore, the shear stress is 0. What will be the applications of this particular thing that we are studying about pressure?

Detailed Explanation

Fluid statics, where there is no relative motion between fluid layers, leads to the understanding that only pressure forces act on submerged surfaces. This concept allows us to calculate pressure variations within reservoirs, forces on submerged surfaces, and even tensile stresses on pipe walls. Knowing how pressure behaves helps in designing safe engineering systems related to fluids.

Examples & Analogies

Think of a large water tank used for irrigation. Understanding how pressure varies allows engineers to design the tank's structure so it can safely hold a certain volume of water without bursting. When you fill it, understanding the pressure at various depths ensures that the walls are thick enough to handle that pressure without any risk of failure.

Significance of Pressure in Engineering Designs

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So, the question is, what are the pressure forces behind the Bhakra Nangal Dam? If this is the first step towards any design, you need to determine the forces or the parameters that determine the stability.

Detailed Explanation

In the context of engineering, understanding pressure is vital for the stability and safety of structures like dams. The Bhakra Nangal Dam serves as a perfect example: the design must account for the pressure exerted by water at different levels, influencing how thick the dam's base needs to be to withstand these forces without collapsing.

Examples & Analogies

Picture a stack of pancakes. If you put a heavy syrup on top of a tall stack, the pancakes at the bottom need to be thicker to support the weight above without crumbling. Similarly, the base of a dam must be thicker to support the immense pressure from the water it holds back.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Pressure increases with depth: The farther down you go in a fluid, the higher the pressure.

  • Pressure is perpendicular: Pressure acts perpendicular to any surface in contact with the fluid.

  • Pascal's Law: Changes in pressure applied to a confined fluid are transmitted equally in all directions.

  • Fluid Statics: In still fluids, shear stress is zero, and pressure forces are the primary forces acting on the fluid.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • When scuba diving, a diver feels increased pressure at greater depths, which is due to the weight of the water above.

  • In the Bhakra Nangal Dam, engineers must consider the varying pressure exerted by the water at different depths to ensure the dam is structurally sound.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Pressure deeper you go, weight adds in a flow, WAD helps you know, pressure on you will grow.

📖 Fascinating Stories

  • Imagine a scuba diver descending into the ocean. As they go deeper, they feel the pressure rising and remember the WAD rule: Weight Above Depth!

🧠 Other Memory Gems

  • Remember 'NPS' for fluids: 'No Shear, just Pressure.' It helps you recall the key concept in fluid statics.

🎯 Super Acronyms

Use WAD to remember the relation

  • Weight Above Depth for pressure increases.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Pressure

    Definition:

    The force applied perpendicular to the surface of an object per unit area.

  • Term: Pascal's Law

    Definition:

    A principle stating that pressure change at any point in a confined fluid is transmitted undiminished in every direction.

  • Term: Hydraulic Engineering

    Definition:

    A field of engineering dealing with the flow and conveyance of fluids, often in relation to water resources.

  • Term: Fluid Statics

    Definition:

    The study of fluids at rest and the forces and pressures in it.

  • Term: Crush Depth

    Definition:

    The maximum depth a submarine can safely operate without being crushed by water pressure.

  • Term: Buoyant Force

    Definition:

    The upward force exerted by a fluid that opposes the weight of an immersed object.