Class 8 Science – Friction: Factors, Advantages, and Disadvantages

1. Introduction

• Friction is the resistance offered by a surface when one object moves over another.

• It opposes motion and occurs between solid surfaces, liquids, or gases.

• Friction is both useful and harmful depending on the situation.

Key Concept:

• Friction arises due to surface roughness and interlocking of microscopic bumps.

2. Factors Affecting Friction

1. Nature of Surfaces

   • Rough surfaces → more friction

   • Smooth surfaces → less friction

2. Normal Force / Weight

   • Heavier objects → higher friction

   • Lighter objects → lower friction

3. Presence of Lubricants

   • Oil, grease, or water → reduce friction

4. Area of Contact

   • Slight effect; friction mainly depends on surface roughness and weight

3. Types of Friction

1. Static Friction

   • Prevents an object from starting motion.

   • Example: A stationary book on a table resists movement.

2. Sliding Friction

   • Opposes motion when object slides on a surface.

   • Example: Pushing a heavy box across the floor.

3. Rolling Friction

   • Resistance faced by a rolling object.

   • Example: Bicycle tires on road, ball rolling on ground.

4. Fluid Friction

   • Resistance faced by an object moving through a liquid or gas.

   • Example: Boat moving through water, air resistance on cars.

4. Advantages of Friction

• Walking and driving: Friction between shoes/tires and ground prevents slipping.

• Holding objects: Friction helps us grip and hold objects.

• Writing and drawing: Friction between pen/pencil and paper.

• Climbing: Enables mountaineers and rock climbers to hold surfaces.

• Vehicle brakes: Friction slows down moving vehicles safely.

5. Disadvantages of Friction

• Wear and tear: Friction causes damage to machine parts.

• Energy loss: Friction reduces efficiency of engines and machines.

• Heating: Excess friction produces unwanted heat.

• Slower motion: Makes moving objects require more effort.

6. Controlling Friction

1. Reducing Friction

   • Use lubricants (oil, grease)

   • Use ball bearings or wheels

   • Polish surfaces

2. Increasing Friction

   • Roughen surfaces for better grip

   • Use treads on shoes or tires

   • Nail spikes, ropes for climbing

Key Concept:

• Friction can be controlled depending on whether we want to increase or decrease it.

7. Key Points to Remember

• Friction opposes motion and is caused by surface irregularities.

• Factors affecting friction: surface type, weight, lubrication.

• Types: Static, sliding, rolling, and fluid friction.

• Advantages: Walking, driving, gripping, braking, writing.

• Disadvantages: Wear, energy loss, heat, slowing motion.

• Friction is necessary for safety and motion control but may need to be reduced in machines.