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8.9 - Pressure Exerted by Liquids and Gases

Interactive Audio Lesson

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Introduction to Pressure from Liquids

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Teacher
Teacher

Today, we’re going to discuss pressure, particularly how liquids exert it. Can anyone tell me what pressure means?

Student 1
Student 1

Is it the force you apply on something?

Teacher
Teacher

Exactly! Pressure is the force applied over an area. Now, why do you think water can exert pressure?

Student 3
Student 3

Because it's heavy, and it pushes down on everything!

Teacher
Teacher

That's right! Water exerts pressure based on its height. The taller the water column, the greater the pressure at the bottom. We can remember this with the acronym HAP: Height Affects Pressure.

Student 2
Student 2

Does that mean a deep pool has more pressure at the bottom than a shallow one?

Teacher
Teacher

Exactly! Let's summarize: The deeper the liquid, the higher the pressure.

Activities Demonstrating Liquid Pressure

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Teacher
Teacher

Now, let’s conduct a simple experiment to see liquid pressure in action. I have a clear pipe and a balloon. Let’s fill it with water and observe what happens.

Student 4
Student 4

I see the balloon is getting pushed outwards!

Teacher
Teacher

Exactly! The pressure from the water is pushing against the rubber. Can anyone relate this to another activity?

Student 1
Student 1

Like when we push the balloon to make it bulge!

Teacher
Teacher

Good connection! Remember, this happens because liquids exert pressure with increasing depth or height. Let's recap: Liquid pressure increases with depth.

Understanding Gas Pressure

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Teacher
Teacher

Now let’s switch gears to gases. How do you think they exert pressure?

Student 3
Student 3

Maybe because they expand and fill their containers?

Teacher
Teacher

Exactly! Gases spread out and push against the walls of their container, creating pressure in all directions. What's a common example of this?

Student 2
Student 2

When we blow air into a balloon!

Teacher
Teacher

Yes! Think about how that air pressure keeps the balloon inflated. Let’s remember GASEP: Gases Apply Pressure Everywhere.

Student 4
Student 4

So, all gases exert pressure, but we don't feel it all the time?

Teacher
Teacher

Correct! The pressure can be felt when the gas is contained. Today's summary: Gases exert pressure in every direction.

Introduction & Overview

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Quick Overview

This section explores the concept of pressure exerted by liquids and gases and how pressure varies with depth and area.

Standard

In this section, we learn that liquids and gases exert pressure on the walls of their containers, and this pressure depends on the height of the liquid column or the amount of gas. Various activities demonstrate these principles, showcasing how pressure behaves in different contexts, such as water-filled bottles and balloons.

Detailed

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Audio Book

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Introduction to Pressure in Liquids and Gases

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Do liquids and gases also exert pressure? Does it also depend on the area on which the force acts? Let us find out.

Detailed Explanation

This chunk introduces the topic of pressure exerted by liquids and gases. It raises questions about whether these substances exert pressure and the relevance of the area over which this pressure acts. Understanding pressure is crucial as it affects how we interact with liquids and gases in our daily lives.

Examples & Analogies

Consider how a soda can is pressurized. When you open it and hear the 'hiss' of gas escaping, it's the pressure inside the can equalizing with the outside atmosphere. This illustrates how gases exert pressure.

Activity 8.8: Observing Pressure from Water

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Activity 8.8 Take a transparent glass tube or a plastic pipe. The length of the pipe/tube should be about 25 cm and its diameter should be 5-7.5 cm. Also take a piece of thin sheet of a good quality rubber, say, a rubber balloon. Stretch the rubber sheet tightly over one end of the pipe. Hold the pipe at the middle, keeping it in a vertical position. Ask one of your friends to pour some water in the pipe. Does the rubber sheet bulge out? Note also the height of the water column in the pipe. Pour some more water. Observe again the bulge in the rubber sheet and the height of the water column in the pipe. Repeat this process a few more times. Can you see any relation between the amount of the bulge in the rubber sheet and the height of the water column in the pipe?

Detailed Explanation

This activity helps students visualize how pressure from water acts on surfaces. As they pour water into the tube, the rubber sheet bulges. The more water added, the higher the water column, and consequently, the more the rubber sheet bulges. This signifies the relationship between liquid height and the pressure it exerts.

Examples & Analogies

Think of how a large balloon inflates when water is poured into it. The more water you add, the more the balloon expands, similar to the rubber sheet bulging out as the water level rises.

Activity 8.9: Pressure in a Closed Container

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Activity 8.9 Take a plastic bottle. You can take a discarded water or soft drink bottle. Fix a cylindrical glass tube, a few cm long near its bottom as shown. Make sure that the water does not leak from the joint. If there is any leakage, seal it with molten wax. Cover the mouth of the glass tube with a thin rubber sheet as you did in Activity 8.8. Now fill the bottle up to half with water. What do you observe? Why does the rubber sheet fixed to the glass tube bulge this time? Pour some more water in the bottle. Is there any change in the bulge of the rubber sheet?

Detailed Explanation

This activity involves observing the behavior of water within a closed container. When water is poured into the bottle, it exerts pressure, causing the rubber sheet at the glass tube's mouth to bulge. The pressure exerted by the water in the bottle is transmitted to the walls and causes the rubber to exert outward. Hence, adding more water changes the bulge proportionately to the increase in pressure.

Examples & Analogies

Imagine a water balloon. When you fill it up, the pressure from the water makes the balloon stretch. Similarly, in this activity, the water pressure makes the rubber sheet bulge outward.

Activity 8.10: Observing Pressure at Different Heights

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Activity 8.10 Take an empty plastic bottle or a cylindrical container. You can take a used tin can or a used plastic bottle. Drill four holes all around near the bottom of the bottle. Make sure that the holes are at the same height from the bottom. Now fill the bottle with water. What do you observe? Do the different streams of water coming out of the holes fall at the same distance from the bottle? What does this indicate?

Detailed Explanation

This activity demonstrates that liquids exert equal pressure at the same depth. As the bottle is filled with water and water flows out of the holes, if all the streams are equal, it shows that pressure at that depth is consistent across these openings. This uniformity indicates that liquid pressure acts equally at the same depth from the surface.

Examples & Analogies

Think about a fountain. The water shoots up from the same height and spreads out evenly. The equal rise from the holes shows how liquid pressure works in real life, just like how the water comes out uniformly from the fountain at equal pressure.

Pressure from Gases

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Do gases also exert pressure? Do they also exert pressure on the walls of their containers? Let us find out.

Detailed Explanation

This chunk prompts students to consider whether gases exert pressure like liquids do. Gases exert pressure in all directions, and this pressure is felt wherever the gas comes into contact with a surface, such as the walls of its container. Understanding gas pressure is crucial in many scientific and practical applications.

Examples & Analogies

When you inflate a balloon, the air inside pushes against the walls of the balloon, making it expand. This pushing against the balloon's surface is an example of gas exerting pressure.

Summary of Liquid and Gas Pressure

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So, we find that gases, too, exert pressure on the walls of their container.

Detailed Explanation

This summary confirms that both liquids and gases exert pressure, impacting how they behave in different contexts like containers and environment. The pressure exerted by these substances is a fundamental concept in physics, highlighting their interaction with the world.

Examples & Analogies

Every time you drink from a straw, you're experiencing the pressure of the liquid being pushed up into your mouth. This is the pressure that liquids and gases exert, at work in our daily lives.

Definitions & Key Concepts

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

Key Concepts

  • Pressure: The force applied over an area.

  • Liquid Pressure: Pressure increases with depth in a liquid.

  • Gas Pressure: Gases exert pressure in all directions.

Examples & Real-Life Applications

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

Examples

  • The pressure at the bottom of a pool is greater than at the surface due to the height of the water column.

  • Inflating a balloon demonstrates how gas pressure keeps it expanded.

Memory Aids

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

🎵 Rhymes Time

  • In the water, down we go, the deeper it is, the more pressure flows.

📖 Fascinating Stories

  • Imagine a fish swimming deeper and deeper, feeling more and more squeezed by the water around it—this represents liquid pressure!

🧠 Other Memory Gems

  • HAP = Height Affects Pressure.

🎯 Super Acronyms

GASEP = Gases Apply Pressure Everywhere.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Pressure

    Definition:

    The force exerted per unit area.

  • Term: Atmospheric Pressure

    Definition:

    The pressure exerted by the weight of air in the atmosphere.

  • Term: Liquid Pressure

    Definition:

    The pressure exerted by a liquid at a given height.

  • Term: Gas Pressure

    Definition:

    The force exerted by gas molecules around a container.