Friction

Friction

• Ever noticed how vehicles slow down when brakes are applied?
• Objects moving on a surface eventually stop on their own.
• Questions like why we slip on a banana peel or find it hard to walk on a wet floor can be answered by understanding friction.

Force of Friction

Factors Affecting Friction

Understanding Friction

• Friction is caused by irregularities on surfaces in contact.
• Even smooth-looking surfaces have tiny bumps.
• These bumps interlock, making movement hard.
• Rougher surfaces have more bumps, increasing friction.
• Pressing surfaces harder increases friction.

Static vs. Sliding Friction

• Static friction: force to start moving an object.
• Sliding friction: force to keep it moving.
• Static friction is higher than sliding friction, making it easier to move an already moving object than to start it from rest.

Do You Know?

Spring Balance

• A tool for measuring force.
• It has a coiled spring that stretches when force is applied.
• The stretch is measured by a pointer on a scale, showing the force’s magnitude.

Friction: A Necessary Evil

Friction: Our Helper and Trouble-Maker

• Holding Objects: Friction helps us hold things like an earthen pot or a glass tumbler. A greasy tumbler is hard to hold due to reduced friction.
• Walking: It’s tough to walk on wet or muddy surfaces without friction. Imagine trying to walk if there was no friction at all!
• Writing: Friction helps us write with pens, pencils, and chalk.
• Moving Objects: Objects wouldn’t stop moving without friction. Cars and bikes need friction between their tires and the road to start, stop, and turn.
• Construction: Nails in walls and tying knots rely on friction. No friction means no buildings!

The Downside of Friction

• Wear and Tear: Friction wears out materials like screws, ball bearings, and shoe soles. Foot over-bridges show worn-out steps due to friction.
• Heat Production: Rubbing palms together generates heat. Mixer jars, matchsticks, and machines get hot due to friction, causing energy wastage.

Increasing and Reducing Friction

Increasing Friction on Purpose

• Shoe Soles: Grooved soles give better grip.
• Treaded Tyres: Provide better grip on roads.
• Brakes: Brake pads in bikes and cars increase friction to stop wheels.
• Sports and Gymnastics: Kabaddi players and gymnasts use coarse substances for better grip.

Reducing Friction

• Powder and Oil: Powder on carrom boards and oil on door hinges reduce friction.
• Grease: Mechanics use grease to make machine parts move smoothly.
• Lubricants: Oil, grease, and graphite form a layer that reduces friction by preventing surfaces from rubbing directly.
• Air Cushion: In some machines, an air cushion is used instead of oil to reduce friction.

Can Friction Be Completely Removed?

• Impossible: Friction can never be fully eliminated. Surfaces always have some irregularities.

Wheels Reduce Friction

Rolling vs. Sliding

• Rolling is Easier: Rolling objects face less resistance than sliding ones.
• Luggage with Rollers: Easier to pull because of rolling friction.
• Wheels: One of the greatest inventions, wheels reduce friction and make movement easier.

Ball Bearings

• Usage: Ball bearings are used in machines to replace sliding with rolling, reducing friction.
• Examples: Found in ceiling fans and bicycles to make them move smoothly.

Fluid Friction

What is Fluid Friction?

• Fluids: Gases and liquids are called fluids in science.
• Friction in Air and Water: Air, water, and other fluids exert frictional force on moving objects.
• Drag: The frictional force exerted by fluids is known as drag.

Factors Affecting Fluid Friction

• Speed: The faster an object moves in a fluid, the greater the frictional force.
• Shape: The shape of the object affects the amount of friction.
• Nature of Fluid: Different fluids exert different amounts of friction.

Minimizing Fluid Friction

• Energy Loss: Objects moving through fluids lose energy due to friction.
• Special Shapes: To minimize friction and save energy, objects are designed with special shapes.
• Nature’s Inspiration: Scientists take inspiration from nature. Birds and fishes have shapes that reduce fluid friction.

Examples in Design

• Aeroplanes: Have shapes similar to birds to reduce air friction.
• Vehicles: Designed to have shapes that cut through air and water efficiently, minimizing drag.

Visual Example

• Aeroplane and Bird: Both have streamlined shapes to move easily through air with less friction. (See Fig. 9.17)

Chapter Summary:

• Friction opposes motion between surfaces in contact.
• It acts on both surfaces involved.
• Friction depends on the nature of the surfaces.
• It also depends on how smooth or rough the surfaces are.
• The force of friction increases with the pressure between surfaces.
• When trying to move an object at rest, static friction comes into play.
• Sliding friction occurs when an object slides over another.
• Sliding friction is less than static friction.
• Friction is essential for many activities.
• Roughening a surface increases friction.
• Treaded soles of shoes and vehicle tires enhance friction.
• Sometimes, friction is unwanted.
• Lubricants can reduce friction.
• Rolling friction occurs when one body rolls over another, and it’s less than sliding friction.
• Ball bearings are used in machines to decrease friction.
• Suitable shapes can minimize fluid friction for objects moving in fluids.

KEYWORDS

1. BALL BEARING
2. DRAG
3. FLUID FRICTION
4. FRICTION
5. INTERLOCKING
6. LUBRICANTS
7. ROLLING FRICTION
8. SLIDING FRICTION
9. STATIC FRICTION