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9.9 - Exercises

Interactive Audio Lesson

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Understanding Friction

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Teacher
Teacher

Today, we're going to talk about friction! Who can tell me what friction does?

Student 1
Student 1

Friction opposes motion!

Teacher
Teacher

That's right! Friction acts against the motion of surfaces in contact. Can anyone give me an example from everyday life?

Student 2
Student 2

When I slide a book across a table, it eventually stops!

Teacher
Teacher

Exactly! The friction between the book and the table is what causes it to slow down. We can remember this with the acronym F.A.S.T: Friction Always Slows Things.

Student 3
Student 3

Does friction always stop things, though?

Teacher
Teacher

Great question! Friction can be both useful and harmful, helping us grip surfaces but also wearing them down. Let's keep exploring this.

Student 4
Student 4

I remember sliding down a slippery slide; it was hard to stop!

Teacher
Teacher

Yes! That leads to the concept of fluid friction which we’ll discuss later. Let's summarize: friction opposes motion and depends on the surfaces in contact.

Types of Friction

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Teacher
Teacher

Now, let's explore the three main types of friction: static, sliding, and rolling. Who can tell me what static friction is?

Student 1
Student 1

It’s the friction when an object is at rest!

Teacher
Teacher

Exactly! Static friction keeps objects at rest from moving until enough force is applied. Student_2, can you explain sliding friction?

Student 2
Student 2

That's when an object is sliding over a surface!

Teacher
Teacher

Yes! Sliding friction is generally less than static friction, making it easier to keep something in motion once it starts. Student_3, how about rolling friction?

Student 3
Student 3

It's when something rolls over a surface instead of sliding!

Teacher
Teacher

Correct! Rolling friction is less than sliding friction, which is why we have wheels. Remember the saying: 'Roll to Reduce'.

Student 4
Student 4

How do we know which type of friction to use in a problem?

Teacher
Teacher

Great follow-up! The type depends on the situation: check if the object is still, sliding, or rolling.

Factors Affecting Friction

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Teacher
Teacher

Let’s uncover what affects friction! Student_1, what do you think influences the friction between two surfaces?

Student 1
Student 1

The texture of the surfaces?

Teacher
Teacher

Right! Rough surfaces create more friction compared to smooth ones. Any other ideas?

Student 2
Student 2

How hard the surfaces are pressed together?

Teacher
Teacher

Excellent point! The harder the surfaces push together, the greater the frictional force. Let’s connect this with our daily lives—why do we make shoes with grips?

Student 3
Student 3

To make it easier to walk without slipping!

Teacher
Teacher

Absolutely! A good grip increases friction and helps us move safely. Remember—'Grip is Key'!

Student 4
Student 4

How does grease help reduce friction?

Teacher
Teacher

Great inquiry! Grease acts as a lubricant, filling in the microscopic grooves of surfaces, reducing interlocking. Let’s remember: 'When in need, grease is the key!'

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section provides exercises aimed at reinforcing the concepts of friction, its types, and the factors affecting it.

Standard

The exercises in this section challenge students to apply their understanding of friction, including its definitions, types, and effects. They cover various scenarios and ask students to analyze and explain these concepts through different types of questions.

Detailed

Youtube Videos

What is Friction? | Class 8th Physics |
What is Friction? | Class 8th Physics |
NCERT Solutions - Friction | Class 8 - Science - Chapter 9
NCERT Solutions - Friction | Class 8 - Science - Chapter 9
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Introduction to Friction | Class 8 I Learn with BYJU'S
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Friction Class 8 Science - Friction Force and its Dependency
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Friction | Class 8 | Physics | Chitti Classes
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What is Friction? | Physics | Infinity Learn
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Why is Friction important in life?? | Anupam sir #shorts #friction #physics #science
Grade 8 | Science | Friction | Free Tutorial | CBSE | ICSE | State Board
Grade 8 | Science | Friction | Free Tutorial | CBSE | ICSE | State Board
NCERT Class 8 Science Chapter 12: Friction | NSO | NSTSE | Olympiad
NCERT Class 8 Science Chapter 12: Friction | NSO | NSTSE | Olympiad
Friction | Full Chapter Revision under 30 mins | Class 8 Science
Friction | Full Chapter Revision under 30 mins | Class 8 Science

Audio Book

Dive deep into the subject with an immersive audiobook experience.

Fill in the Blanks

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  1. Fill in the blanks.
    (a) Friction opposes the ___ between the surfaces in contact with each other.
    (b) Friction depends on the     __ of surfaces.
    (c) Friction produces     _.
    (d) Sprinkling of powder on the carrom board __ friction.
    (e) Sliding friction is _____ than the static friction.

Detailed Explanation

This exercise encourages students to recall key facts about friction.
- The first blank emphasizes that friction obstructs movement between surfaces.
- The second blank focuses on understanding that the nature of the surfaces affects friction.
- The third blank requires students to identify the effects of friction, such as heat generation.
- The fourth blank relates to how certain substances can reduce friction.
- The final blank helps reinforce the idea that sliding friction is typically lower than static friction.

Examples & Analogies

Think about sliding down a slide at a playground. The surface of the slide and your speed determine how fast you go. A smooth slide (like one without friction) would let you slide down quickly, while a rough slide (like one with friction) would slow you down because the friction is opposing your motion.

Choosing the Correct Arrangement

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  1. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.
    (a) rolling, static, sliding
    (b) rolling, sliding, static
    (c) static, sliding, rolling
    (d) sliding, static, rolling

Detailed Explanation

This exercise tests students' understanding of the relative strengths of different types of friction. Generally:
- Static friction is the strongest as it prevents motion from starting.
- Sliding friction is weaker because it allows movement but still opposes it.
- Rolling friction is the weakest since it involves wheels or spheres that rotate instead of sliding.
Students need to identify that the correct order is (c) static, sliding, rolling.

Examples & Analogies

Consider a heavy sofa. When you try to push it, you first have to overcome static friction — this is hard! Once it starts moving, you face sliding friction, which is easy but still present. If you were to put the sofa on a rolling dolly, moving it becomes much easier because rolling friction is at play.

Observing Friction on Different Surfaces

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  1. Alida runs her toy car on dry marble floor, wet marble floor, newspaper, and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be:
    (a) wet marble floor, dry marble floor, newspaper and towel.
    (b) newspaper, towel, dry marble floor, wet marble floor.
    (c) towel, newspaper, dry marble floor, wet marble floor.
    (d) wet marble floor, dry marble floor, towel, newspaper

Detailed Explanation

This question helps students understand how surface texture impacts friction. Wet surfaces generally reduce friction compared to dry surfaces. The increasing order of friction would typically follow this logic, leading students to determine that the correct answer is (c) towel, newspaper, dry marble floor, wet marble floor, since the towel is the most absorbent and least frictional.

Examples & Analogies

Picture trying to move a toy car on different carpets—some are plush, which creates more resistance, while others are flat. A wet or polished floor can feel slippery compared to a rough, dry one, similar to how their toy car behaves when running over those surfaces.

Direction of Friction Force

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  1. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of the frictional force acting on it.

Detailed Explanation

In this situation, as the book slides down due to gravity, the frictional force will act in the opposite direction of the slide — that is, upwards along the desk surface. This opposing force is crucial as it seeks to slow down the book's descent. Students should illustrate this concept by drawing an arrow pointing upward along the desk surface.

Examples & Analogies

Think about riding a bicycle up a hill. As you pedal harder, gravity tries to pull you down. The friction between your tires and the road pushes you up, opposing gravity's pull - just like the friction for the sliding book.

Effects of Soapy Water on Marble Floor

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  1. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?

Detailed Explanation

Soapy water creates a slippery layer on the marble, significantly reducing friction. Consequently, it becomes more difficult to walk as your feet have less grip on the floor. Thus, students should answer that walking becomes challenging due to decreased friction.

Examples & Analogies

Imagine trying to walk on ice versus a rough pavement. Trying to maintain balance on a slippery floor is similar to trying to walk on ice — you would slide instead of grip the surface.

Purpose of Shoes with Spikes

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  1. Explain why sportsmen use shoes with spikes.

Detailed Explanation

Spikes are designed to dig into the ground, which increases friction between the shoe and the surface. Therefore, when athletes sprint or change direction, they have better control and stability. This innovation greatly helps in various sports by enhancing performance.

Examples & Analogies

Think about a race car’s tires; they are designed for maximum grip on the road. Similarly, spikes on shoes provide that essential grip for sports, preventing slipping and allowing for quick movements.

Comparative Force Application for Pushing Boxes

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  1. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Detailed Explanation

Seema will have to apply a larger force to push her heavier box due to increased static friction. Static friction depends on the weight of the box, which means the harder pressing force makes it more difficult to start moving. This exercise elaborates on Newton's second law relating force, mass, and acceleration.

Examples & Analogies

Consider lifting a full backpack versus an empty one. The full backpack requires more effort due to its weight—pushing a heavy box is similarly strenuous compared to a lighter one.

Static vs. Sliding Friction Explanation

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  1. Explain why sliding friction is less than static friction.

Detailed Explanation

Static friction is greater because it has to overcome the 'interlocking' or 'locking' of microscopic surface irregularities. Once those surfaces start sliding against each other, the surfaces move past these interlocks, reducing the frictional force required to maintain motion. Thus, sliding friction is generally less than static friction.

Examples & Analogies

Imagine trying to move a heavy piece of furniture. Taking that first step is tough, equivalent to static friction. Once it's in motion, it's easier to slide across the floor — that’s the sliding friction at work!

Friction as Both a Friend and a Foe

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  1. Give examples to show that friction is both a friend and a foe.

Detailed Explanation

Friction serves as a friend in various scenarios, such as allowing us to walk without slipping and enabling vehicles to stop. However, it can be a foe as well, causing wear and tear and generating unwanted heat in machinery. This contrast illustrates that while friction is essential, it can also lead to inefficiency. Understanding these dual roles fosters a comprehensive view of friction's impact.

Examples & Analogies

Think of friction as a reliable friend who helps you climb a steep hill (like walking) but can also dance a little too close and cause a fall (like excessive wear on a moving part).

Shapes of Objects Moving in Fluids

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  1. Explain why objects moving in fluids must have special shapes.

Detailed Explanation

To minimize fluid friction, objects like boats and airplanes are designed with aerodynamic shapes that reduce drag. For example, a streamlined shape not only helps vehicles move faster through air or water but also enhances fuel efficiency. Understanding this allows students to appreciate the application of physics in engineering.

Examples & Analogies

Consider how a fish swims; its body is streamlined naturally to cut through water smoothly. Engineers mimic nature by designing cars and airplanes to have similar fluid shapes.

Definitions & Key Concepts

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

Key Concepts

  • Friction: The force opposing motion between surfaces.

  • Static Friction: Keeps objects at rest from moving.

  • Sliding Friction: Occurs between sliding surfaces.

  • Rolling Friction: Found when objects roll over surfaces.

Examples & Real-Life Applications

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

Examples

  • The friction between a car's tires and the road allows the car to stop safely.

  • Using a skateboard on a smooth surface results in less friction than on a rough surface.

Memory Aids

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

🎵 Rhymes Time

  • Friction's the force that slows it down, without it we'd surely slip and frown.

📖 Fascinating Stories

  • Once there was a hero named Friction who always stopped uninvited slides, helping everyone stand and glide!

🧠 Other Memory Gems

  • Remember 'S.S.R' for Static, Sliding, Rolling friction types.

🎯 Super Acronyms

F.A.S.T

  • Friction Always Slows Things.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Friction

    Definition:

    The force that opposes the relative motion between two surfaces in contact.

  • Term: Static Friction

    Definition:

    The friction that exists between a stationary object and the surface it's on.

  • Term: Sliding Friction

    Definition:

    The friction that occurs when two surfaces slide against each other.

  • Term: Rolling Friction

    Definition:

    The friction that occurs when an object rolls over a surface.