Science Class 8 - Friction Notes

Friction

Welcome to the chapter on Friction for Class 8. In this chapter, you will learn what friction is, how it affects our daily life, its advantages and disadvantages, and ways to increase or decrease friction. By the end of this chapter, you will understand the importance of friction and how it works in the world around us!

Introduction

Friction is a force that opposes the motion of one object over another. It acts when two surfaces touch each other. Friction can slow things down or stop them from moving.

What is Friction?

Friction is the resistance that one surface or object encounters when moving over another. It is caused by the roughness of surfaces and the force pressing them together.

• Friction acts in the opposite direction to movement.
• It is present everywhere—on roads, in machines, and even in the air.

Types of Friction

• Static Friction: The force that keeps an object at rest.
• Sliding Friction: The force when an object slides over another.
• Rolling Friction: The force when an object rolls over another.
• Fluid Friction: The force when an object moves through a fluid (liquid or gas).

Advantages of Friction

• Helps us walk without slipping.
• Allows vehicles to move on roads.
• Enables us to write with a pen or pencil.
• Helps in holding and gripping objects.

Disadvantages of Friction

• Causes wear and tear of moving parts.
• Produces unwanted heat in machines.
• Reduces the efficiency of engines and machines.

Ways to Increase Friction

• Making surfaces rougher (e.g., using sandpaper).
• Using rubber soles on shoes.
• Adding treads to tires.

Ways to Decrease Friction

• Making surfaces smoother.
• Using lubricants like oil or grease.
• Using ball bearings in machines.

Fun Activity: Friction Test!

Try sliding a book on a smooth table and then on a rough carpet. Which one is easier? This shows how friction changes with different surfaces!

Summary

• Friction is a force that opposes motion.
• It has both advantages and disadvantages.
• We can increase or decrease friction as needed.

Practice Questions

1. What is friction?
2. Name two advantages of friction.
3. How can we reduce friction in machines?
4. What type of friction acts when a ball rolls on the ground?
5. Why do tires have treads?

Challenge Yourself

• List three examples where friction is useful in daily life.
• Explain why friction is sometimes a problem in machines.

Did You Know?

• Without friction, you would not be able to walk or write!
• Friction can produce heat, which is why rubbing your hands together makes them warm.

Glossary

• Friction: A force that opposes motion between two surfaces.
• Lubricant: A substance that reduces friction.
• Wear and Tear: Damage caused by friction over time.
• Ball Bearing: A device that helps reduce friction in machines.

Answers to Practice Questions

1. Friction is a force that opposes the motion of objects.
2. It helps us walk and allows vehicles to move on roads.
3. By using lubricants or ball bearings.
4. Rolling friction.
5. To increase friction and prevent slipping.

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Observe how friction works around you and think about its uses and effects!