Force and Motion Explained: Meaning, Types, Laws and Applications for JKSSB

Force and motion are among the most fundamental concepts in physics and form an important part of the General Science syllabus for JKSSB Finance Accounts Assistant and other competitive examinations. Every activity around us, from walking and driving a vehicle to the movement of planets and satellites, involves force and motion in some way.

Force is responsible for changing the state of rest or motion of an object, while motion describes the change in the position of an object with time. Understanding these concepts helps explain many natural phenomena and everyday activities. Questions related to types of force, types of motion, Newton’s Laws of Motion, inertia, momentum, friction, speed, velocity, and acceleration are frequently asked in competitive examinations.

Introduction to Force and Motion

Force and motion are closely related concepts in physics. Motion refers to the change in the position of an object with time, while force is an external influence that can change the state of motion or rest of an object. Whenever an object starts moving, stops moving, speeds up, slows down, or changes direction, a force is involved.

For example, a football remains at rest until it is kicked. The kick applies a force that causes the ball to move. Similarly, brakes apply force to stop a moving vehicle. These examples show how force affects motion in our daily lives.

The study of force and motion helps us understand the working of vehicles, machines, sports activities, satellites, and many natural phenomena. Knowledge of these concepts forms the foundation for understanding Newton’s Laws of Motion and other important topics in physics.

Key Points

• Force is a push or pull acting on an object.
• Motion is the change in the position of an object with time.
• Force can start, stop, accelerate, decelerate, or change the direction of motion.
• Both force and motion are essential for understanding physical phenomena around us.
• Questions related to force and motion are frequently asked in JKSSB and other competitive examinations.

What is Force?

Force is a push or pull acting on an object that can change its state of rest or motion. It is one of the most fundamental concepts in physics and is responsible for almost every movement that occurs around us. Whenever we push a door, pull a rope, kick a football, lift a bag, or apply brakes to a vehicle, we are exerting force.

According to physics, force is an external agent that can alter the velocity, direction, shape, or size of an object. An object at rest will remain at rest, and an object in motion will continue moving with the same speed and direction unless acted upon by an external force. This principle forms the basis of Newton’s First Law of Motion.

Force is a vector quantity, meaning it possesses both magnitude and direction. For example, applying a force of 10 Newtons towards the east is different from applying the same force towards the west because the direction changes.

In everyday life, force plays an important role in activities such as walking, driving, lifting objects, playing sports, and operating machines. Without force, no object could start moving, stop moving, or change its direction.

SI Unit of Force

The International System (SI) unit of force is the Newton (N). It is named after the famous English scientist Sir Isaac Newton, who formulated the laws of motion.

One Newton is defined as the force required to produce an acceleration of 1 metre per second squared (1 m/s²) in a body of mass 1 kilogram (1 kg).

1 Newton = 1 kg × 1 m/s²

Formula of Force

Force is calculated using Newton’s Second Law of Motion.

F = m × a

Where:

• F = Force (Newton)
• m = Mass of the object (kg)
• a = Acceleration produced (m/s²)

Example

If a force acts on a body of mass 5 kg and produces an acceleration of 2 m/s²:

F = 5 × 2 = 10 N

Therefore, the force acting on the body is 10 Newtons.

Characteristics of Force

Force possesses several important characteristics that help us understand its effects on objects.

1. Force Has Magnitude and Direction

Since force is a vector quantity, both magnitude and direction are necessary to describe it completely. A force of 20 N towards the north is different from a force of 20 N towards the south.

2. Force Can Change the State of Rest

An object lying at rest can be made to move by applying force.

Example: A stationary football starts moving when kicked.

3. Force Can Change the State of Motion

A moving object can be stopped, accelerated, or slowed down by applying force.

Example: Brakes stop a moving vehicle by applying force.

4. Force Can Change the Direction of Motion

The direction of a moving object can be altered by force.

Example: A batsman changes the direction of a cricket ball by hitting it with a bat.

5. Force Can Change the Shape or Size of an Object

Force can deform objects by stretching, compressing, bending, or twisting them.

Examples:

• Stretching a rubber band
• Compressing a spring
• Squeezing a sponge

6. Force Can Act Through Contact or Without Contact

Some forces require physical contact, while others can act from a distance.

Examples:

• Muscular force and frictional force are contact forces.
• Gravitational force and magnetic force are non-contact forces.

Effects of Force

The application of force can produce several effects on an object.

1. Force Can Move a Stationary Object

When force is applied to an object at rest, it may start moving.

Example: Pushing a trolley causes it to move.

2. Force Can Stop a Moving Object

A moving object can be brought to rest by applying force opposite to its motion.

Example: Applying brakes stops a bicycle.

3. Force Can Increase the Speed of an Object

Force can accelerate an object and make it move faster.

Example: Pressing the accelerator increases the speed of a car.

4. Force Can Decrease the Speed of an Object

Force can reduce the speed of a moving object.

Example: Friction slows down a rolling ball.

5. Force Can Change the Direction of Motion

The path of a moving object can be altered.

Example: A football changes direction when struck by a player.

6. Force Can Change Shape and Size

Force can deform objects temporarily or permanently.

Example: Kneading dough changes its shape.

Examples of Force in Daily Life

Importance of Force in Daily Life

• Helps us walk, run, and jump.
• Enables transportation through vehicles.
• Allows machines to perform work.
• Plays a crucial role in sports and games.
• Helps in lifting and carrying objects.
• Responsible for the motion of planets and satellites.

Exam-Oriented One-Liners

• Force is a push or pull acting on an object.
• Force is a vector quantity.
• SI unit of force is Newton (N).
• Force is measured using a spring balance.
• Newton is named after Sir Isaac Newton.
• Force can change the speed, direction, shape, and size of an object.
• Force can be contact or non-contact.
• Formula of force: F = ma.
• One Newton is the force required to accelerate a 1 kg mass by 1 m/s².
• Gravitational force is a non-contact force.

Frequently Asked MCQ

Q. The SI unit of force is:

(a) Joule
(b) Newton
(c) Watt
(d) Pascal

Answer: (b) Newton

What is Motion?

Motion is the change in the position of an object with respect to time and a reference point. If an object changes its position continuously over time, it is said to be in motion. Motion is one of the most common phenomena observed in our daily lives. From a moving car and a flying bird to the rotation of the Earth and the revolution of planets around the Sun, motion is present everywhere.

To determine whether an object is in motion or at rest, a reference point is required. For example, a person sitting inside a moving bus appears to be at rest relative to other passengers but is in motion relative to a person standing on the roadside. Thus, motion is a relative concept and depends on the observer’s frame of reference.

The study of motion helps us understand how objects move, how fast they move, and how their position changes over time. It forms the foundation for understanding concepts such as speed, velocity, acceleration, and Newton’s Laws of Motion.

Reference Point in Motion

A reference point is a fixed point or object used to determine whether another object is moving or stationary.

Examples

• A train moving relative to a railway station is in motion.
• A person sitting in a moving train is at rest relative to fellow passengers but in motion relative to the ground.
• The Earth appears stationary to us, but it is constantly moving around the Sun.

Characteristics of Motion

Motion has several important characteristics:

1. Change in Position

An object is said to be in motion only if its position changes with time.

Example: A car travelling on a road changes its position continuously.

2. Motion Requires Time

Motion can only be described when there is a change in position over a period of time.

Example: A runner covers a certain distance in a given time interval.

3. Motion is Relative

The state of motion depends on the observer and the chosen reference point.

Example: A passenger sitting in a moving bus appears stationary to another passenger but moving to a person standing outside.

4. Motion Can Occur in Different Directions

Objects can move in straight lines, circular paths, or irregular paths.

Examples:

• A train moving on a straight track.
• A fan rotating around its axis.
• A butterfly flying randomly.

Rest and Motion

An object is said to be at rest if its position does not change with time relative to a reference point.

An object is said to be in motion if its position changes with time relative to a reference point.

Examples of Motion in Daily Life

• A car moving on a road.
• A cyclist riding a bicycle.
• A bird flying in the sky.
• A train moving on railway tracks.
• A child swinging on a swing.
• The Earth rotating on its axis.
• The Earth revolving around the Sun.

Importance of Studying Motion

The study of motion is important because it helps us:

• Understand the movement of vehicles and machines.
• Explain the motion of planets, satellites, and stars.
• Design transportation systems.
• Analyze sports and athletic activities.
• Develop scientific and engineering applications.

Exam-Oriented One-Liners

• Motion is the change in position of an object with time.
• Motion is always measured with respect to a reference point.
• Motion is a relative concept.
• An object can be at rest for one observer and in motion for another.
• Time and reference point are essential to describe motion.
• The Earth rotates on its axis and revolves around the Sun.
• Motion forms the basis of speed, velocity, and acceleration.

Frequently Asked MCQ

Q. An object is said to be in motion when:

(a) Its shape changes
(b) Its mass changes
(c) Its position changes with time
(d) Its colour changes

Answer: (c) Its position changes with time

Types of Motion

Motion is the change in the position of an object with time. However, all objects do not move in the same manner. Some move in a straight line, some move in circles, while others move back and forth repeatedly. Based on the path followed and the nature of movement, motion is classified into different types.

Understanding the types of motion helps us explain the movement of vehicles, machines, planets, and many natural phenomena. Questions related to types of motion are commonly asked in JKSSB Finance Accounts Assistant and other competitive examinations.

1. Rectilinear Motion

Rectilinear motion is the motion of an object along a straight-line path. The word “rectilinear” is derived from the Latin words rectus meaning straight and linea meaning line.

In this type of motion, an object moves only in one direction along a straight path. The direction remains unchanged unless an external force acts on the object.

Examples

• A train moving on a straight railway track.
• A car travelling on a straight road.
• A stone falling vertically towards the Earth.
• An elevator moving up or down.

Characteristics of Rectilinear Motion

• Motion occurs along a straight line.
• The shortest distance between two points is covered.
• Direction remains constant.
• It is the simplest form of motion.

Importance

Rectilinear motion is commonly observed in transportation systems and is frequently used in solving numerical problems related to speed, velocity, and acceleration.

2. Circular Motion

Circular motion is the motion of an object along a circular path around a fixed point or axis.

In circular motion, even if the speed of the object remains constant, its direction changes continuously. Since velocity depends on both speed and direction, the velocity of the object is constantly changing.

A force known as centripetal force acts towards the centre of the circle and keeps the object moving along the circular path.

Examples

• The hands of a clock.
• A satellite revolving around the Earth.
• A stone tied to a string and whirled in a circle.
• The blades of a fan.

Characteristics of Circular Motion

• The object moves along a circular path.
• Direction changes continuously.
• Velocity changes continuously.
• Requires centripetal force.

Importance

Circular motion is observed in planetary motion, amusement rides, satellites, and rotating machinery.

3. Rotational Motion

Rotational motion occurs when an object rotates about its own axis.

In this type of motion, every point of the object moves in a circular path around the axis of rotation. The object itself does not move from one place to another; instead, it spins about a fixed axis.

Examples

• A ceiling fan rotating.
• A spinning top.
• The Earth rotating on its axis.
• A potter’s wheel.

Characteristics of Rotational Motion

• Motion occurs around a fixed axis.
• Every particle of the object moves in a circular path.
• The axis may be real or imaginary.
• All parts of the object rotate simultaneously.

Importance

Rotational motion is important in machines, engines, turbines, wheels, and many mechanical devices.

4. Oscillatory Motion

Oscillatory motion is the to-and-fro motion of an object about its mean or equilibrium position.

The object repeatedly moves between two extreme positions and returns to its original position after a fixed interval of time.

Examples

• A swinging pendulum.
• A child on a swing.
• Vibrations of a tuning fork.
• Vibrations of a guitar string.

Characteristics of Oscillatory Motion

• Motion is repetitive.
• Occurs about a fixed mean position.
• The object moves between two extreme positions.
• Generally periodic in nature.

Importance

Oscillatory motion is used in clocks, musical instruments, and scientific instruments.

5. Periodic Motion

Periodic motion is the motion that repeats itself after equal intervals of time.

A motion is called periodic when an object returns to its initial position after a fixed time period and the same motion repeats again and again.

All oscillatory motions are periodic because they repeat after regular intervals, but some periodic motions may not be oscillatory.

Examples

• Revolution of the Earth around the Sun.
• Rotation of the Earth on its axis.
• Movement of clock hands.
• Motion of a pendulum.

Characteristics of Periodic Motion

• Repeats at regular intervals.
• Has a definite time period.
• Predictable in nature.
• Commonly observed in natural phenomena.

Importance

Periodic motion helps in measuring time and understanding astronomical events.

6. Random Motion

Random motion is the motion in which an object moves in an irregular and unpredictable manner.

There is no fixed path, direction, or pattern in this type of motion. The movement keeps changing continuously and cannot be predicted accurately.

Examples

• Movement of a butterfly.
• Motion of dust particles in air.
• Movement of mosquitoes.
• Brownian motion of pollen grains in water.

Characteristics of Random Motion

• No definite path.
• Direction changes continuously.
• Unpredictable in nature.
• Irregular movement.

Importance

Random motion helps scientists understand the behaviour of gases, liquids, and microscopic particles.

Difference Between Circular Motion and Rotational Motion

Difference Between Oscillatory Motion and Periodic Motion

Importance of Studying Types of Motion

Knowledge of different types of motion helps us:

• Understand the working of machines and vehicles.
• Explain planetary and satellite motion.
• Study transportation systems.
• Analyze sports and athletic movements.
• Develop engineering and technological applications.

Frequently Asked MCQ

Q. Which type of motion is exhibited by a swinging pendulum?

(a) Rectilinear motion
(b) Circular motion
(c) Oscillatory motion
(d) Random motion

Answer: (c) Oscillatory motion

Distance and Displacement

Distance and displacement are two of the most important concepts in the study of motion. They help us describe how far an object has moved and where it is located relative to its starting position. Although these terms are often used interchangeably in everyday language, they have distinct meanings in physics.

Understanding the difference between distance and displacement is essential because many concepts such as speed, velocity, acceleration, and motion are based on them. Questions related to distance and displacement are frequently asked in JKSSB, SSC, Railway, and other competitive examinations.

For example, if a person walks around a park and returns to the starting point, the total path covered may be quite large, but the person’s displacement will be zero because the initial and final positions are the same. This simple example highlights the difference between distance and displacement.

What is Distance?

Distance is the total length of the actual path travelled by an object during its motion, irrespective of the direction of movement.

In simple words, distance tells us “how much ground has been covered” by an object while moving from one place to another.

Distance does not take direction into account. It only considers the total path followed by the object.

Definition

Distance is the total path length travelled by an object between its initial and final positions.

Formula of Distance

Distance can be calculated using:

Distance = Speed × Time

Where:

• Distance is measured in metres (m).
• Speed is measured in metres per second (m/s).
• Time is measured in seconds (s).

SI Unit of Distance

The SI unit of distance is metre (m).

Other commonly used units are:

• Kilometre (km)
• Centimetre (cm)
• Millimetre (mm)

Examples of Distance

Example 1

A person walks:

• 100 metres towards the east
• Then 50 metres towards the west

The total path covered is:

Distance = 100 m + 50 m

Distance = 150 m

Example 2

A student walks around a circular playground once.

If the circumference of the playground is 200 metres, then:

Distance travelled = 200 metres

Example 3

A car moves at a speed of 60 km/h for 2 hours.

Distance = Speed × Time

Distance = 60 × 2

Distance = 120 km

Characteristics of Distance

• Distance is the actual path travelled.
• It is a scalar quantity.
• It has magnitude only.
• It is always positive.
• It cannot be zero if an object has moved.
• Distance is always greater than or equal to displacement.

What is Displacement?

Displacement is the shortest straight-line distance between the initial position and the final position of an object, measured in a specific direction.

Unlike distance, displacement tells us not only how far an object has moved but also in which direction it has moved.

Displacement depends only on the starting and ending positions of the object and does not depend on the actual path followed.

Definition

Displacement is the shortest distance from the initial position to the final position of an object along with direction.

Formula of Displacement

Displacement = Final Position − Initial Position

SI Unit of Displacement

The SI unit of displacement is metre (m).

Examples of Displacement

Example 1

A person walks:

• 100 metres east
• Then 50 metres west

The final position is 50 metres east of the starting point.

Therefore:

Displacement = 50 metres east

Example 2

A runner completes one full round of a circular track and returns to the starting point.

• Initial position = Final position

Therefore:

Displacement = 0

Example 3

A student walks 30 metres north and then returns 30 metres south to the starting point.

Distance travelled = 60 metres

Displacement = 0

This example clearly shows that distance and displacement can have different values.

Characteristics of Displacement

• It is the shortest distance between two points.
• It is a vector quantity.
• It has both magnitude and direction.
• It may be positive, negative, or zero.
• It can never be greater than distance.
• It may be zero even when distance is not zero.

Why Distance and Displacement Are Different

Distance depends on the actual path travelled by an object.

Displacement depends only on the initial and final positions of the object.

For example, if a person moves from point A to point B using different routes, the distance travelled may vary, but the displacement remains the same because the starting and ending points remain unchanged.

Difference Between Distance and Displacement

Numerical Example

Suppose a student walks:

• 40 metres east
• Then 30 metres west

Distance Travelled

Distance = 40 + 30

Distance = 70 metres

Displacement

Displacement = 40 − 30

Displacement = 10 metres east

Therefore:

• Distance = 70 metres
• Displacement = 10 metres east

Special Case: Circular Motion

Consider a runner completing one full round of a circular track.

Distance

Distance = Circumference of the track

Displacement

Since the runner returns to the starting point:

Displacement = 0

This is one of the most frequently asked examination concepts.

Importance of Distance and Displacement

The concepts of distance and displacement are important because they:

• Form the basis of motion studies.
• Help calculate speed and velocity.
• Are used in transportation and navigation.
• Help describe the movement of objects accurately.
• Distinguish between scalar and vector quantities.

Exam-Oriented One-Liners

• Distance is the total path travelled by an object.
• Displacement is the shortest distance between initial and final positions.
• Distance is a scalar quantity.
• Displacement is a vector quantity.
• Distance has only magnitude.
• Displacement has magnitude and direction.
• Distance is always positive.
• Displacement can be positive, negative, or zero.
• Distance is always greater than or equal to displacement.
• Displacement can never exceed distance.
• If an object returns to its starting point, displacement becomes zero.
• SI unit of distance and displacement is metre (m).
• Speed is based on distance.
• Velocity is based on displacement.

Frequently Asked MCQ

Q. A person walks 100 metres east and then 100 metres west, returning to the starting point. What is the displacement?

(a) 100 m
(b) 200 m
(c) 50 m
(d) 0 m

Answer: (d) 0 m

Speed and Velocity

Speed and velocity are important concepts used to describe how fast an object moves. Although these terms are often used interchangeably in everyday life, they have different meanings in physics. Understanding the difference between speed and velocity is essential because many numerical and conceptual questions in JKSSB Finance Accounts Assistant and other competitive examinations are based on these topics.

Speed tells us how fast an object is moving, whereas velocity tells us how fast an object is moving in a particular direction. Thus, velocity provides more complete information about motion because it includes both magnitude and direction.

What is Speed?

Speed is the distance travelled by an object per unit time.

In simple words, speed indicates how quickly an object covers a certain distance. It does not provide any information about the direction of motion.

Definition

Speed is defined as the rate at which distance is covered by an object.

Formula of Speed

Speed = Distance ÷ Time

Mathematically:

Speed = d / t

Where:

• d = Distance travelled
• t = Time taken

SI Unit of Speed

The SI unit of speed is metre per second (m/s).

Other commonly used units are:

• Kilometre per hour (km/h)
• Centimetre per second (cm/s)

Example

A car travels a distance of 120 km in 2 hours.

Speed = Distance ÷ Time

Speed = 120 ÷ 2

Speed = 60 km/h

Characteristics of Speed

• Speed is a scalar quantity.
• It has only magnitude.
• Direction is not considered.
• Speed is always positive or zero.
• It indicates how fast an object moves.

Types of Speed

1. Uniform Speed

An object is said to have uniform speed if it covers equal distances in equal intervals of time.

Example: A train travelling at a constant speed of 60 km/h.

2. Non-Uniform Speed

An object has non-uniform speed if it covers unequal distances in equal intervals of time.

Example: A car moving through city traffic.

3. Average Speed

Average speed is the total distance travelled divided by the total time taken.

Average Speed = Total Distance ÷ Total Time

Example

A car travels:

• 100 km in 2 hours
• 60 km in 1 hour

Average Speed = (100 + 60) ÷ (2 + 1)

Average Speed = 160 ÷ 3

Average Speed = 53.33 km/h

What is Velocity?

Velocity is the displacement of an object per unit time in a specified direction.

Unlike speed, velocity includes both magnitude and direction. Therefore, velocity is a vector quantity.

Definition

Velocity is defined as the rate of change of displacement with respect to time.

Formula of Velocity

Velocity = Displacement ÷ Time

Mathematically:

Velocity = s / t

Where:

• s = Displacement
• t = Time taken

SI Unit of Velocity

The SI unit of velocity is metre per second (m/s).

Example

A person moves 100 metres east in 20 seconds.

Velocity = 100 ÷ 20

Velocity = 5 m/s east

The direction “east” must be specified because velocity is a vector quantity.

Characteristics of Velocity

• Velocity is a vector quantity.
• It has both magnitude and direction.
• It depends on displacement.
• It may be positive, negative, or zero.
• A change in direction changes velocity even if speed remains constant.

Types of Velocity

1. Uniform Velocity

An object is said to have uniform velocity if it covers equal displacements in equal intervals of time in the same direction.

Example: A train moving in a straight line at a constant speed.

2. Variable Velocity

An object has variable velocity if either its speed or direction changes.

Example: A car moving around a curved road.

Difference Between Speed and Velocity

Relationship Between Speed and Velocity

• Speed and velocity have the same SI unit.
• Speed is based on distance.
• Velocity is based on displacement.
• Average speed is always greater than or equal to the magnitude of average velocity.
• When an object moves in a straight line without changing direction, speed and velocity have the same numerical value.

Importance of Speed and Velocity

The concepts of speed and velocity help us:

• Study the motion of vehicles.
• Understand transportation systems.
• Analyze sports performance.
• Calculate travel time.
• Understand advanced concepts such as acceleration and momentum.

Exam-Oriented One-Liners

• Speed is the distance travelled per unit time.
• Velocity is the displacement per unit time.
• Speed is a scalar quantity.
• Velocity is a vector quantity.
• SI unit of speed is m/s.
• SI unit of velocity is m/s.
• Speed depends on distance.
• Velocity depends on displacement.
• Direction is necessary for velocity but not for speed.
• Average speed is total distance divided by total time.
• Uniform velocity requires constant speed and constant direction.
• A change in direction causes a change in velocity.

Frequently Asked MCQ

Q. Which of the following is a vector quantity?

(a) Distance
(b) Speed
(c) Velocity
(d) Time

Answer: (c) Velocity

Acceleration and Retardation (Deceleration)

In everyday life, we often observe objects increasing or decreasing their speed. A car speeds up when the accelerator is pressed, slows down when brakes are applied, and a cyclist may gradually come to rest due to friction. The concept that describes the change in velocity of an object is known as acceleration.

Acceleration is one of the most important concepts in the study of motion because it explains how quickly the velocity of an object changes with time. When velocity increases, the object is said to be accelerating. When velocity decreases, the object experiences retardation or deceleration.

Questions based on acceleration and retardation are frequently asked in JKSSB and other competitive examinations, both in theory and numerical form.

What is Acceleration?

Acceleration is the rate of change of velocity with respect to time.

In simple words, acceleration tells us how quickly an object’s velocity increases or decreases over a given period of time.

Definition

Acceleration is defined as the change in velocity per unit time.

Formula of Acceleration

Acceleration is calculated using:

Acceleration = Change in Velocity ÷ Time Taken

Mathematically:

a = (v − u) / t

Where:

• a = Acceleration
• u = Initial velocity
• v = Final velocity
• t = Time taken

SI Unit of Acceleration

The SI unit of acceleration is:

metre per second squared (m/s²)

This means the velocity changes by a certain number of metres per second every second.

Example of Acceleration

A car increases its speed from 10 m/s to 30 m/s in 5 seconds.

Given:

• Initial velocity (u) = 10 m/s
• Final velocity (v) = 30 m/s
• Time (t) = 5 s

Using the formula:

a = (30 − 10) / 5

a = 20 / 5

a = 4 m/s²

Therefore, the acceleration of the car is 4 m/s².

Characteristics of Acceleration

• Acceleration is a vector quantity.
• It has both magnitude and direction.
• It can be positive, negative, or zero.
• It occurs whenever velocity changes.
• A change in speed or direction causes acceleration.

Types of Acceleration

1. Positive Acceleration

When the velocity of an object increases with time, the acceleration is called positive acceleration.

Examples:

• A car speeding up on a highway.
• A train leaving a station.
• A cyclist pedalling faster.

Characteristics

• Final velocity is greater than initial velocity.
• Speed increases with time.
• Acceleration has a positive value.

2. Negative Acceleration

When the velocity of an object decreases with time, the acceleration is called negative acceleration.

Negative acceleration is commonly known as retardation or deceleration.

Examples:

• Applying brakes to a vehicle.
• A ball rolling on the ground and gradually stopping.
• A train slowing down before reaching a station.

3. Uniform Acceleration

An object is said to have uniform acceleration if its velocity changes by equal amounts in equal intervals of time.

Example:

A freely falling body under gravity (ignoring air resistance).

Characteristics

• Rate of change of velocity remains constant.
• Acceleration has a fixed value.

4. Non-Uniform Acceleration

When the velocity changes by unequal amounts in equal intervals of time, the object has non-uniform acceleration.

Examples:

• A car moving in city traffic.
• A motorcycle moving through crowded streets.

Characteristics

• Rate of change of velocity varies.
• Acceleration is not constant.

What is Retardation (Deceleration)?

Retardation or deceleration is the rate at which the velocity of an object decreases with time.

It is simply negative acceleration because it acts opposite to the direction of motion and reduces the speed of the object.

Formula of Retardation

Retardation = (Initial Velocity − Final Velocity) ÷ Time

Mathematically:

Retardation = (u − v) / t

Example of Retardation

A car slows down from 25 m/s to 5 m/s in 4 seconds.

Given:

• Initial velocity = 25 m/s
• Final velocity = 5 m/s
• Time = 4 s

Retardation = (25 − 5) / 4

Retardation = 20 / 4

Retardation = 5 m/s²

Therefore, the retardation of the car is 5 m/s².

Difference Between Acceleration and Retardation

Acceleration Due to Gravity

When an object falls freely towards the Earth, it experiences acceleration due to gravity.

This acceleration is denoted by g.

Value of g:

g = 9.8 m/s²

This means the velocity of a freely falling object increases by 9.8 m/s every second.

Examples

• Falling fruits from a tree.
• A stone dropped from a height.
• Rain falling towards the Earth.

Importance of Acceleration in Daily Life

Acceleration plays a vital role in:

• Transportation systems.
• Vehicle design and safety.
• Sports and athletics.
• Aviation and space science.
• Machine operation and engineering.

Numerical Example

A motorcycle increases its velocity from 15 m/s to 35 m/s in 10 seconds.

Given:

• u = 15 m/s
• v = 35 m/s
• t = 10 s

Acceleration = (35 − 15) / 10

Acceleration = 20 / 10

Acceleration = 2 m/s²

Therefore, the acceleration of the motorcycle is 2 m/s².

Exam-Oriented One-Liners

• Acceleration is the rate of change of velocity.
• Formula of acceleration: a = (v − u)/t.
• SI unit of acceleration is m/s².
• Acceleration is a vector quantity.
• Positive acceleration increases speed.
• Retardation decreases speed.
• Retardation is also called negative acceleration.
• Uniform acceleration means constant acceleration.
• Acceleration due to gravity is represented by g.
• Value of g on Earth is approximately 9.8 m/s².
• A freely falling body experiences acceleration due to gravity.
• Change in direction also produces acceleration.

Frequently Asked MCQ

Q. The SI unit of acceleration is:

(a) m/s
(b) m²/s
(c) m/s²
(d) N/m

Answer: (c) m/s²

Newton’s Laws of Motion

Newton’s Laws of Motion are the three fundamental laws that explain the relationship between force and motion. These laws were given by the famous English physicist Sir Isaac Newton in his book Principia Mathematica in 1687.

These laws explain how objects behave when forces act upon them. They help us understand why objects remain at rest, why they start moving, why their speed changes, and why they change direction.

Newton’s Laws are the foundation of classical mechanics and are widely used in physics, engineering, transportation, space science, and daily life activities.

The three laws of motion are:

1. Newton’s First Law of Motion (Law of Inertia)
2. Newton’s Second Law of Motion
3. Newton’s Third Law of Motion

Newton’s First Law of Motion (Law of Inertia)

Newton’s First Law states:

“An object remains at rest or continues in a state of uniform motion in a straight line unless acted upon by an external unbalanced force.”

This law explains the natural tendency of objects to resist any change in their state of motion.

In simple words:

• A stationary object will remain stationary.
• A moving object will continue moving with the same speed and direction.
• A force is required to change the state of an object.

Explanation of First Law

According to this law, objects do not change their motion by themselves. They need an external force to:

• Start moving.
• Stop moving.
• Increase or decrease speed.
• Change direction.

For example, a football lying on the ground will not move unless someone kicks it. Similarly, a moving bicycle will continue moving for some time even after pedalling stops because of inertia.

Inertia

The tendency of an object to resist any change in its state of rest or motion is called inertia.

Inertia depends on the mass of an object.

Greater the mass of an object, greater will be its inertia.

For example:

• A truck has more inertia than a bicycle because it has greater mass.
• It is easier to stop a bicycle than a truck moving at the same speed.

Types of Inertia

1. Inertia of Rest

The tendency of an object at rest to remain at rest is called inertia of rest.

Examples:

• When a bus suddenly starts, passengers fall backward.
• A coin placed on a card falls into a glass when the card is pulled quickly.

Explanation:

The passengers’ bodies are initially at rest. When the bus starts suddenly, the lower part of the body moves with the bus, but the upper part tends to remain at rest, causing them to fall backward.

2. Inertia of Motion

The tendency of a moving object to continue moving is called inertia of motion.

Examples:

• Passengers fall forward when a moving bus stops suddenly.
• A ball rolling on the ground continues moving for some time.

Explanation:

When the bus stops suddenly, the lower part of the passenger’s body stops with the bus, but the upper part continues moving forward due to inertia.

3. Inertia of Direction

The tendency of an object to continue moving in the same direction is called inertia of direction.

Examples:

• Passengers are pushed sideways when a car takes a sharp turn.
• Water droplets leave a rotating umbrella tangentially.

Newton’s Second Law of Motion

Newton’s Second Law gives the relationship between force, mass, and acceleration.

It states:

“The rate of change of momentum of an object is directly proportional to the applied force and occurs in the direction of the force.”

This law explains how much force is required to move an object.

Momentum

Momentum is the quantity of motion possessed by a moving object.

It depends on:

• Mass of the object.
• Velocity of the object.

Formula of Momentum

Momentum = Mass × Velocity

p = mv

Where:

p = Momentum
m = Mass
v = Velocity

SI Unit of Momentum

The SI unit of momentum is: kg m/s

Mathematical Form of Second Law

According to Newton’s Second Law: Force is proportional to the rate of change of momentum.

F ∝ (Change in momentum / Time)

Since: Momentum = Mass × Velocity

The formula becomes: F = ma

Where:

F = Force
m = Mass
a = Acceleration

Explanation of F = ma

The formula shows:

1. Force is directly proportional to acceleration

If mass remains constant:

• More force produces more acceleration.
• Less force produces less acceleration.

Example:

A football moves faster when kicked with greater force.

2. Acceleration is inversely proportional to mass

For the same force:

• A lighter object accelerates more.
• A heavier object accelerates less.

Example:

It is easier to push a bicycle than a truck.

Examples of Newton’s Second Law

Kicking a Football

A football has small mass, so a small force produces large acceleration.

Pushing a Heavy Cart

A heavy cart requires more force because it has greater mass.

Catching a Cricket Ball

A player moves hands backward while catching the ball.

This increases the stopping time and reduces the force of impact.

Newton’s Third Law of Motion

Newton’s Third Law states: “For every action, there is an equal and opposite reaction.”

This means forces always occur in pairs. When one object applies force on another object, the second object applies an equal force in the opposite direction.

Explanation of Third Law

Action and reaction forces:

• Occur at the same time.
• Have equal magnitude.
• Act in opposite directions.
• Act on different objects.

Examples of Newton’s Third Law

1. Walking

While walking:

• Our feet push the ground backward.
• The ground pushes us forward.

This reaction force helps us move forward.

2. Swimming

A swimmer pushes water backward.

The water pushes the swimmer forward.

3. Rocket Launch

A rocket pushes gases downward.

The gases push the rocket upward.

This reaction force lifts the rocket into space.

4. Gun Recoil

When a bullet is fired:

• The bullet moves forward.
• The gun moves backward.

The backward movement of the gun is called recoil.

Applications of Newton’s Laws in Daily Life

Newton’s Laws explain many everyday activities:

Walking

Based on the Third Law of Motion.

Vehicle Movement

Engines produce force that changes the motion of vehicles.

Seat Belts in Cars

Seat belts protect passengers due to inertia.

When a car stops suddenly, the body tends to move forward.

Rocket Propulsion

Based on Newton’s Third Law.

Sports

Movement of balls, bats, and players depends on forces.

Difference Between Newton’s Three Laws

Exam-Oriented One-Liners

• Newton’s Laws of Motion were given by Sir Isaac Newton.
• First Law is also called the Law of Inertia.
• Inertia depends on mass.
• Greater mass means greater inertia.
• Second Law gives the formula F = ma.
• SI unit of force is Newton.
• Momentum = Mass × Velocity.
• Third Law states every action has an equal and opposite reaction.
• Walking is an application of Newton’s Third Law.
• Rocket propulsion works on Newton’s Third Law.
• Seat belts are related to inertia.
• Force changes the state of motion of an object.

Q. Passengers fall forward when a moving bus suddenly stops due to:

(a) Friction
(b) Inertia of motion
(c) Gravity
(d) Acceleration

Answer: (b) Inertia of motion

Applications of Force and Motion in Daily Life

Force and motion are not limited to textbooks; they are present in almost every activity we perform. From walking and running to driving vehicles and launching satellites, every movement around us involves the application of force.

The concepts of force, motion, speed, velocity, acceleration, and Newton’s Laws of Motion help us understand how objects behave in real-life situations. Questions based on daily life applications of force and motion are often asked in competitive examinations such as JKSSB Finance Accounts Assistant, SSC, and other exams.

1. Walking and Running

Walking and running are examples of Newton’s Third Law of Motion.

When we walk:

• Our feet push the ground backward.
• The ground applies an equal and opposite force on our feet.
• This reaction force moves us forward.

Without friction between our feet and the ground, walking would not be possible.

Example:

A person cannot walk properly on a slippery surface because there is insufficient frictional force.

2. Movement of Vehicles

Vehicles move because forces act on them.

When the engine of a vehicle produces force:

• The wheels push the road backward.
• The road pushes the wheels forward.
• The vehicle moves ahead.

Acceleration in Vehicles

When the driver presses the accelerator:

• Engine force increases.
• Velocity increases.
• The vehicle accelerates.

When brakes are applied:

• Frictional force acts opposite to motion.
• Speed decreases.
• The vehicle stops.

3. Seat Belts and Inertia

Seat belts in vehicles are based on Newton’s First Law of Motion.

When a moving vehicle suddenly stops:

• The vehicle stops due to braking force.
• The passenger’s body tends to continue moving forward due to inertia.

The seat belt provides an opposing force and prevents the passenger from being thrown forward.

4. Launching of Rockets

Rocket motion is based on Newton’s Third Law of Motion.

During rocket launch:

• The rocket pushes hot gases downward.
• The gases exert an equal and opposite force on the rocket.
• The rocket moves upward.

This principle is called rocket propulsion.

5. Throwing a Ball

Throwing a ball involves force and motion.

When force is applied:

• The ball changes from rest to motion.
• Greater force produces greater acceleration.

The direction in which the ball moves depends on the direction of applied force.

6. Playing Sports

Many sports activities involve force and motion.

Cricket

When a batsman hits a ball:

• Force from the bat changes the speed and direction of the ball.

Football

When a player kicks a football:

• Force moves the stationary ball.
• Direction depends on the force applied.

Hockey

A hockey stick applies force to change the motion of the puck.

7. Falling Objects

Objects fall towards Earth due to gravitational force.

Examples:

• Falling of fruits from trees.
• Dropping a stone.
• Rainfall.

The acceleration produced due to Earth’s gravity is:

g = 9.8 m/s²

This means the speed of a freely falling object increases by 9.8 m/s every second.

8. Braking of Vehicles

Braking works due to frictional force.

When brakes are applied:

• Brake pads create friction.
• Friction acts opposite to the motion.
• The vehicle slows down and stops.

The faster the vehicle moves, the greater the stopping distance required.

9. Swimming

Swimming is an example of Newton’s Third Law.

During swimming:

• A swimmer pushes water backward.
• Water pushes the swimmer forward.

The reaction force helps the swimmer move.

10. Flying of Birds and Aircraft

Flying involves forces acting in different directions.

The four main forces involved in flight are:

1. Lift
2. Weight
3. Thrust
4. Drag

Lift

The upward force that helps an aircraft rise.

Weight

The downward gravitational force.

Thrust

The forward force produced by engines.

Drag

The resistance offered by air.

11. Opening and Closing Doors

Opening a door involves applying force.

• Pushing the door moves it away.
• Pulling the door brings it closer.

The amount of force required depends on the distance from the hinge.

A door opens more easily when pushed near the handle because the turning effect of force is greater.

12. Stretching a Rubber Band

When a rubber band is stretched:

• Force changes its shape.
• Elastic force develops inside the rubber band.
• When released, it returns to its original shape.

This shows that force can change the shape of an object.

13. Motion of Planets and Satellites

The movement of planets and satellites is controlled by gravitational force.

Examples:

• Earth revolves around the Sun.
• Moon revolves around Earth.
• Artificial satellites orbit Earth.

Gravity provides the necessary centripetal force for circular motion.

14. Use of Force in Machines

Machines work by applying forces.

Examples:

• Cranes lift heavy objects.
• Motors rotate machines.
• Pumps move liquids.

Mechanical advantage allows machines to perform tasks with less effort.

Importance of Force and Motion

The study of force and motion helps us:

• Design vehicles and machines.
• Understand natural phenomena.
• Improve safety systems.
• Develop technology.
• Explain movement in living and non-living things.

Exam-Oriented One-Liners

• Walking is based on Newton’s Third Law.
• Seat belts work due to inertia.
• Rocket propulsion is based on Newton’s Third Law.
• Friction helps vehicles stop.
• Gravity causes objects to fall.
• Acceleration due to gravity is 9.8 m/s².
• Force can change speed, direction, and shape.
• Vehicles accelerate due to applied force.
• Swimming is an application of action and reaction.
• Aircraft movement involves lift, thrust, weight, and drag.
• Planets move due to gravitational force.

Frequently Asked MCQ

Q. Rocket propulsion is based on which law of motion?

(a) Newton’s First Law
(b) Newton’s Second Law
(c) Newton’s Third Law
(d) Law of Gravitation

Answer: (c) Newton’s Third Law

Important Formulas for JKSSB Exams

For JKSSB Finance Accounts Assistant and other competitive examinations, numerical questions from Force and Motion are usually based on basic formulas. Remembering these formulas helps aspirants solve problems quickly and accurately.

The following formulas are the most important ones from this chapter.

1. Formula of Force

Force is the product of mass and acceleration.

Formula:

Force = Mass × Acceleration

F = m × a

Where:

• F = Force (Newton)
• m = Mass of object (kg)
• a = Acceleration (m/s²)

SI Unit:

Newton (N)

Example:

If a body of mass 5 kg produces an acceleration of 2 m/s²:

F = 5 × 2

F = 10 N

Therefore, force acting on the body is 10 Newton.

2. Formula of Speed

Speed tells us how fast an object is moving.

Formula:

Speed = Distance ÷ Time

Speed = d/t

Where:

• d = Distance travelled
• t = Time taken

SI Unit:

metre per second (m/s)

Example:

A car travels 100 metres in 20 seconds.

Speed = 100 ÷ 20

Speed = 5 m/s

3. Formula of Velocity

Velocity is the rate of change of displacement with time.

Unlike speed, velocity includes direction.

Formula:

Velocity = Displacement ÷ Time

Velocity = s/t

Where:

• s = Displacement
• t = Time taken

SI Unit:

m/s

Example:

A person moves 50 metres towards east in 10 seconds.

Velocity = 50 ÷ 10

Velocity = 5 m/s east

4. Formula of Acceleration

Acceleration measures the change in velocity per unit time.

Formula:

Acceleration = Change in Velocity ÷ Time

a = (v − u)/t

Where:

• a = Acceleration
• v = Final velocity
• u = Initial velocity
• t = Time taken

SI Unit:

m/s²

Example:

A car increases its velocity from 10 m/s to 30 m/s in 5 seconds.

a = (30 − 10)/5

a = 20/5

a = 4 m/s²

5. Formula of Momentum

Momentum is the quantity of motion possessed by a moving object.

Formula:

Momentum = Mass × Velocity

p = m × v

Where:

• p = Momentum
• m = Mass
• v = Velocity

SI Unit:

kg m/s

Example:

A body of mass 4 kg moves with a velocity of 5 m/s.

Momentum = 4 × 5

Momentum = 20 kg m/s

Important Formula Summary Table

Conclusion: Force and Motion Quick Revision

Force and Motion are fundamental concepts of physics that help us understand the movement and behaviour of objects around us. From simple activities like walking and running to complex processes like rocket launches and satellite movement, every motion involves the application of force.

For JKSSB Finance Accounts Assistant preparation, it is important to understand the basic definitions, formulas, laws, and applications rather than memorising only facts.

Key Points to Remember

• Force is a push or pull that can change the state of rest or motion of an object.
• The SI unit of force is Newton (N).
• Force is calculated using the formula:

F = ma

• Motion refers to the change in position of an object with respect to time.
• Motion is classified into:
  • Rectilinear motion
  • Circular motion
  • Rotational motion
  • Oscillatory motion
  • Periodic motion
  • Random motion
• Distance is the total path travelled, while displacement is the shortest distance between two positions.
• Speed is distance travelled per unit time.
• Velocity is displacement per unit time.
• Acceleration is the change in velocity with time.

Frequently Asked Questions (FAQ) – Force and Motion

Q1. What is force in physics?

Force is a push or pull acting on an object that can change its state of rest or motion, speed, direction, shape, or size.

Q2. What is the SI unit of force?

The SI unit of force is Newton (N).

One Newton is the force required to produce an acceleration of 1 m/s² in a body of mass 1 kg.

Q3. Is force a scalar or vector quantity?

Force is a vector quantity because it has both magnitude and direction.

Q4. What is motion?

Motion is the change in position of an object with respect to a reference point over time.

Q5. What is the difference between distance and displacement?

Distance is the total path travelled by an object, while displacement is the shortest straight-line distance between the initial and final positions.

Distance is a scalar quantity, whereas displacement is a vector quantity.

Q6. What is the formula of force?

The formula of force is:

F = m × a

Where:

F = Force
m = Mass
a = Acceleration

Q7. What are the types of motion?

The main types of motion are:

• Rectilinear Motion
• Circular Motion
• Rotational Motion
• Oscillatory Motion
• Periodic Motion
• Random Motion

Q8. What is Newton’s First Law of Motion?

Newton’s First Law states that an object remains at rest or continues in uniform motion unless acted upon by an external unbalanced force.

It is also called the Law of Inertia.

Q9. What is inertia?

Inertia is the tendency of an object to resist any change in its state of rest or motion.

The greater the mass of an object, the greater its inertia.

Q10. What are the three types of inertia?

The three types of inertia are:

1. Inertia of Rest
2. Inertia of Motion
3. Inertia of Direction

Q11. What is Newton’s Second Law of Motion?

Newton’s Second Law explains the relationship between force, mass, and acceleration.

The formula is:

F = ma

Q12. What does Newton’s Third Law state?

Newton’s Third Law states:

“For every action, there is an equal and opposite reaction.”

Examples include walking, swimming, and rocket propulsion.

Q13. What is momentum?

Momentum is the quantity of motion possessed by a moving object.

Formula:

Momentum = Mass × Velocity

p = mv

Q14. What is the SI unit of momentum?

The SI unit of momentum is:

kg m/s

Q15. What is acceleration?

Acceleration is the rate of change of velocity with time.

Formula:

a = (v-u)/t

SI unit:

m/s²

Q16. What is friction?

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

Q17. Why is friction useful?

Friction helps in:

• Walking
• Writing
• Braking vehicles
• Holding objects

Without friction, movement would become difficult.

Q18. Which forces are non-contact forces?

Non-contact forces include:

• Gravitational force
• Magnetic force
• Electrostatic force

Q19. What is the difference between speed and velocity?

Speed is distance travelled per unit time, while velocity is displacement per unit time.

Speed is scalar, whereas velocity is vector.

Q20. What are the important formulas of Force and Motion?

Important formulas:

• Force = Mass × Acceleration
• Speed = Distance ÷ Time
• Velocity = Displacement ÷ Time
• Acceleration = Change in Velocity ÷ Time
• Momentum = Mass × Velocity

Q21. Why do passengers fall forward when a bus stops suddenly?

Passengers fall forward due to inertia of motion. The body tries to continue moving even after the bus stops.

Q22. Rocket launch is based on which law of motion?

Rocket propulsion works on Newton’s Third Law of Motion.

Q23. What is the acceleration due to gravity on Earth?

The acceleration due to gravity is approximately:

9.8 m/s²

Q24. What happens to displacement when a person completes one full circular path and returns to the starting point?

The displacement becomes zero because the initial and final positions are the same.

Q25. Why is force important in daily life?

Force helps in:

• Movement of vehicles
• Sports activities
• Operation of machines
• Walking and running
• Space technology

About The Author

Rohit Thapa

See author's posts