Force Class 6 ICSE Selina Physics

Class 6 ICSE Physics

Force and Friction: Selina Concise Physics Exercise 3

Complete objective, short-answer, long-answer and think-and-answer solutions with tap-to-reveal explanations.

Start Exercise Revise Concepts

Concepts Objective Fill in the blanks True or False Match Short Answers Long Answers Think and Answer FAQ

1

Quick Concept Revision

F

Force

A push or pull with both magnitude and direction.

C

Contact Force

Acts when objects touch, such as friction or muscular force.

N

Non-contact Force

Acts from a distance, such as gravity, magnetism or electrostatic force.

R

Friction

Opposes relative motion between surfaces in contact.

Remember: The SI unit of force and weight is the newton (N), while kilogram (kg) is a unit of mass.

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2

Objective Type Questions

Read each question, choose an option and then open the answer.

Question 1(a)

A body falls downwards because of:

AElectrical force

BGravitational force

CMechanical force

DMagnetic force

Show answer and reason

Correct answer: Gravitational force

Reason: Earth attracts the body towards its centre due to gravity, so an unsupported body falls vertically downwards.

Question 1(b)

A force does not change:

AMass

BLength

CShape

DState of motion

Show answer and reason

Correct answer: Mass

Reason: A force may change motion, direction, speed, shape or size, but it does not change the mass of the body.

Question 1(c)

A force is expressed correctly by stating:

AOnly its magnitude

BOnly its direction

CBoth magnitude and direction

DNone of these

Show answer and reason

Correct answer: Both magnitude and direction

Reason: Force is a vector quantity, so both its magnitude and direction are required.

Question 1(d)

Friction:

APromotes motion

BOpposes relative motion

CAlways acts in the direction of motion

DIs always a nuisance

Show answer and reason

Correct answer: Opposes relative motion

Reason: Friction opposes the relative motion, or the tendency of relative motion, between surfaces in contact.

Question 1(e)

In the context of the given options, friction is reduced by:

AMaking the surfaces wet

BMaking the surfaces dry

CMaking the surfaces rough

DSprinkling sand on the surface

Show answer and reason

Correct answer: Making the surfaces wet

Reason: A thin liquid layer can act as a lubricant and reduce direct interlocking between surface irregularities. This effect depends on the surfaces and the liquid.

Question 1(f)

Friction:

ACauses wear and tear

BProduces heat

CCan stop a moving body

DHas all the above disadvantages

Show answer and reason

Correct answer: Has all the above disadvantages

Reason: Friction can oppose motion, cause wear and tear, and convert mechanical energy into heat.

Question 1(g)

Friction is increased if:

AOil is sprayed

BThe surfaces are made wet

CThe surfaces are made dry

DThe surfaces are polished

Show answer and reason

Correct answer: The surfaces are made dry

Reason: Among these options, dry surfaces generally provide more friction than wet, oiled or polished surfaces.

3

Fill in the Blanks

1. (a) Force is applied as ______ or ______.
2. (b) On squeezing a gum tube, its ______ changes.
3. (c) On pulling a stretchable string, its ______ increases.
4. (d) When a moving football is kicked from another direction, its ______ changes.
5. (e) On applying brakes to a moving car, its speed ______.
6. (f) We use ball bearings to ______ friction.
7. (g) Friction ______ motion.
8. (h) Lubricants are used to ______ friction.
9. (i) Friction causes ______ of moving machine parts.

AnswersOpen the completed statements

1. (a) push; pull
2. (b) shape
3. (c) length
4. (d) direction of motion
5. (e) decreases or slows down
6. (f) reduce
7. (g) opposes
8. (h) reduce
9. (i) wear and tear

4

True or False

Statement (a)

The frictional force always acts in the direction of motion of a body.

Reveal answer

False. Friction opposes relative motion or the tendency of relative motion between surfaces.

Statement (b)

The unit of weight is kilogram.

Reveal answer

False. Kilogram is a unit of mass. The SI unit of weight is newton (N). Kilogram-force (kgf) and gram-force (gf) are gravitational units of force.

Statement (c)

A force can change the direction of motion of a moving body.

Reveal answer

True. A force applied in a different direction can change the body's direction of motion.

Statement (d)

A force increases the mass of a body when applied to it.

Reveal answer

False. Applying a force does not change the body's mass.

Statement (e)

The force of friction is always disadvantageous.

Reveal answer

False. Friction is useful for walking, writing, gripping objects and applying brakes.

Statement (f)

Sliding friction is greater than rolling friction.

Reveal answer

True. For the same surfaces and load, rolling friction is generally less than sliding friction.

Statement (g)

Liquids generally offer more resistance to motion than gases.

Reveal answer

True. At this level, gases are treated as offering less fluid friction than liquids.

Statement (h)

A wet oily road offers more friction than a dry rough road.

Reveal answer

False. Water or oil usually reduces grip, while a dry rough road generally provides greater friction.

5

Match the Following

Column A	Correct match from Column B
1. Non-contact force	Gravitational force
2. Like poles	Repel
3. Contact force	Force of friction
4. Mass	kg
5. Weight	kgf (gravitational unit); N in SI
6. Friction	Wear and tear

6

Short Answer Type

Tap a question to reveal its answer.

Question 1Name the term used for a push or pull.

Force.

Question 2Give one example each of force as a push, pull, stretch and squeeze.

1. Push: Pushing a door to open it.
2. Pull: A rickshaw puller pulling a rickshaw.
3. Stretch: Stretching a spring so that it elongates.
4. Squeeze: Squeezing a toothpaste tube so that its shape changes.

Question 3Explain the meaning of force.

A force is a push or pull that can change, or tend to change, the state of rest, speed, direction, shape or size of a body. A force has both magnitude and direction.

Question 4What effect can a force have on a stationary body?

A force can make a stationary body move. For example, a football lying on the ground starts moving when it is kicked.

Question 5What effects can a force have on a moving body?

• A force opposite to motion can slow down or stop the body.
• A force in the direction of motion can increase its speed.
• A force applied in another direction can change its direction of motion.

Question 6What effect can a force produce on a body that is not allowed to move?

It can deform the body by changing its shape or size. For example, squeezing a rubber ball changes its shape.

Question 7Give one example each to show that force produces motion, stops motion, slows motion, changes direction and deforms a body.

1. Produces motion: A stationary ball moves when kicked.
2. Stops motion: A fielder stops a moving cricket ball by catching it.
3. Slows motion: Brakes slow a moving bicycle.
4. Changes direction: A hockey stick deflects a moving ball.
5. Deforms a body: Squeezing rubber changes its shape.

Question 8State the effect produced by force in each case: a stretched catapult sling, a pushed cart, a deflected ball, a cyclist applying brakes and a compressed spring.

1. Catapult sling: Its shape changes and its length increases.
2. Heavy cart: Its state of rest changes; it starts moving or speeds up.
3. Deflected ball: Its direction of motion changes.
4. Cyclist applying brakes: The cycle slows down and may stop.
5. Compressed spring: Its shape changes and its length decreases.

Question 9Name the two kinds of forces in nature.

The two broad kinds are contact forces and non-contact forces.

Question 10Name the type of force acting in each case.

Situation	Type of force
A porter lifts luggage	Muscular force
A bicycle slows when pedalling stops	Frictional force
A stone falls from a roof	Gravitational force
A rubbed comb attracts paper bits	Electrostatic force
A string supports a hanging load	Tension force
A horse moves a cart	Muscular force
A magnet attracts an iron pin	Magnetic force
A boy opens a door	Muscular force
An apple falls from a tree	Gravitational force
A person rows a boat	Muscular force

Question 11Define the weight of a body.

The weight of a body is the gravitational force with which Earth attracts it. Its SI unit is the newton (N). The gravitational unit kilogram-force (kgf) is also used in some school texts.

Question 12What is friction?

Friction is the force that opposes relative motion, or the tendency of relative motion, between two surfaces in contact.

Question 13Give an example that illustrates the existence of friction.

When a cyclist stops pedalling, the bicycle gradually slows and stops because friction and air resistance oppose its motion.

Question 14What causes friction?

Friction mainly arises from the interlocking of tiny irregularities on contacting surfaces and from adhesion between those surfaces.

Question 15State two factors that directly affect friction between solid surfaces.

• The nature and roughness of the surfaces in contact.
• The force pressing the surfaces together, which usually increases with load or weight.

Note: Fluid friction also depends on factors such as the nature of the fluid, speed and shape of the moving body.

Question 16When is friction between a truck and the road greater: when the truck is empty or loaded?

Friction is generally greater when the truck is loaded because the tyres and road are pressed together with a greater normal force.

Question 17Which offers more friction: a glass surface or a wooden surface?

A wooden surface generally offers more friction because it is rougher and has more surface irregularities than smooth glass.

Question 18Name the three kinds of friction.

Static friction, sliding friction and rolling friction.

Question 19List three disadvantages of friction.

• It opposes motion, so extra force or energy may be required.
• It causes wear and tear of moving parts.
• It produces unwanted heat and reduces efficiency.

Question 20List three ways of reducing friction.

• Make surfaces smoother.
• Use suitable lubricants.
• Use rollers or ball bearings to replace sliding with rolling.

Question 21Give three examples showing that friction is a necessary evil.

• Friction lets us walk without slipping.
• Friction helps a ladder remain supported against a wall and the ground.
• Friction is needed to light a matchstick.

It is called a necessary evil because it is essential in many activities but also causes wear, heat and energy loss.

Question 22Define static, sliding and rolling friction.

1. Static friction: The friction that prevents a stationary object from starting to move. Its maximum value just before motion begins is called limiting friction.
2. Sliding friction: The friction acting when one surface slides over another.
3. Rolling friction: The friction that opposes the rolling motion of an object over a surface.

Question 23Arrange static, sliding and rolling friction in descending order.

Static friction > Sliding friction > Rolling friction

7

Long Answer Type

Question 1What is gravitational force? Give an example.

Gravitational force is the attractive force between any two objects that have mass. Near Earth, it pulls objects towards Earth's centre. The weight of a body is the gravitational force exerted on it by Earth.

Example: A fruit falls from a tree towards the ground because Earth attracts it gravitationally.

Question 2Why does a bicycle stop and why do its wheel rims become hot when brakes are applied?

When brakes are applied, the brake pads press against the wheel rims. Friction opposes the rotation of the wheels, slowing and finally stopping the bicycle. Friction also converts some mechanical energy into heat, so the rims and brake pads become warm.

Question 3Why does an eraser become smaller with use?

Friction acts when the eraser rubs against paper. Tiny particles of eraser material wear away while removing graphite marks. Repeated rubbing causes continuous wear, so the eraser gradually becomes smaller.

Question 4Why is it difficult to open an inkpot with greasy or oily hands?

Oil acts as a lubricant and reduces friction between the fingers and the lid. With less friction, the fingers cannot grip the lid firmly enough to turn it easily.

Question 5Why is it difficult to walk on a wet road?

A layer of water can reduce friction between shoes and the road. Because walking requires sufficient friction for grip, the feet may slip more easily on a wet surface.

Question 6A body needs force F1 to start moving, F2 to keep sliding and F3 to roll. Identify the frictions and compare F2 with F1 and F3.

Static or limiting frictionF1

Sliding frictionF2

Rolling frictionF3

Since static friction is generally greater than sliding friction, F2 < F1. Since sliding friction is generally greater than rolling friction, F2 > F3.

F1 > F2 > F3

Question 7Explain why friction is both a necessity and an evil.

Friction as a necessity

• It helps us walk.
• It enables writing.
• It allows brakes to stop vehicles.
• It helps us hold and grip objects.

Friction as an evil

• It wears out machine parts.
• It wastes useful energy as heat.
• It may cause overheating.
• It makes movement harder.

Therefore, friction is essential for everyday life, but it also causes damage and energy loss.

8

Think and Answer

Think and Answer 1

For a successful rocket launch from Earth's surface, the rocket must overcome:

AEarth's electrostatic force

BEarth's gravitational force

CAtmospheric friction or air resistance

DBoth gravitational force and atmospheric resistance

Show answer and reason

Correct answer: Both gravitational force and atmospheric resistance

Reason: Thrust must overcome Earth's downward gravitational pull and the drag produced by the atmosphere during ascent.

Think and Answer 2

Choose the decreasing order of rolling, static and sliding friction.

ARolling, static, sliding

BRolling, sliding, static

CStatic, sliding, rolling

DSliding, static, rolling

Show answer and reason

Correct answer: Static, sliding, rolling

Reason: For the same surfaces and load, the usual school-level order is static friction greater than sliding friction greater than rolling friction.

Think and Answer 3

With mustard oil on your hands, which object is likely to be hardest to hold?

AEarthen cup

BThermocol tumbler

CWooden cup

DGlass tumbler

Show answer and reason

Correct answer: Glass tumbler

Reason: Oil reduces grip, and smooth glass already offers relatively little friction, making the tumbler especially slippery.

9

Frequently Asked Questions

What is force in Class 6 Physics?

Force is a push or pull that can change the motion, direction, shape or size of a body.

What are contact and non-contact forces?

Contact forces act only when bodies touch, while non-contact forces such as gravitational, magnetic and electrostatic forces can act from a distance.

What is the SI unit of force and weight?

The SI unit of both force and weight is the newton, written as N. Kilogram is a unit of mass, not weight.

Why is friction called a necessary evil?

Friction is necessary for walking, writing, gripping and braking, but it also causes wear, heat and energy loss.

Which is greatest: static, sliding or rolling friction?

For the same surfaces and load, the usual order is static friction greater than sliding friction greater than rolling friction.

How can friction be reduced?

Friction can be reduced by smoothing surfaces, applying suitable lubricants and using rollers or ball bearings.

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Educational answers have been edited for scientific clarity and age-appropriate understanding.

Concept by Teacher Ritu, designed by Shaleen Shekhar.