NCERT Class 11 Physics Chapter 3 Notes Motion in a straight Line - Download PDF

Revision Notes for CBSE Class 11 Physics Chapter 2: Motion in a Straight Line - Free PDF Download

Strong conceptual clarity is necessary to score highly in a chapter, and success depends on mastering the subject. In order to assist students succeed, Careers360 experts have carefully developed Class 11 Physics Chapter 2 notes on Motion in a Straight Line.

These notes are a great resource for both CBSE school examinations and competitive exams like JEE Mains, NEET, and WBJEE. They are in line with the most recent CBSE Class 11 Physics Syllabus (2025–26). These notes, which are based on the NCERT textbook, provide a thorough and organized approach to the chapter.

The Motion in a Straight Line Class 11 notes cover topics including displacement, velocity, and equations of motion in class 11 notes in an orderly manner. They can also be used by students at any time, from any location, even without an internet connection, because they are available in PDF format. These notes guarantee complete understanding and quick review, which improves learning effectiveness and accessibility.

Also Read,

• NCERT Solutions for Class 11 Physics Chapter 2 Motion in a Straight Line
• NCERT Exemplar Class 11 Physics Chapter 2 Motion in a Straight Line

NCERT Class 11 Physics Chapter 2 Notes

Rest and Motion

An object is said to be at rest if it remains stationary in relation to a specific frame of reference over time. On the other hand, if an object's position relative to a frame of reference changes over time, it is said to be in motion. A coordinate system to which observers attach coordinates to describe events and observations is referred to as a frame of reference.

Frame of Reference

A frame of reference is a coordinate system used to describe the position and motion of objects by providing a set of axes relative to an observer's perspective.

According to the frame of reference:

A body is considered in motion if its position changes over time relative to that frame, and it is considered at rest if there is no change in its position within that frame of reference. For instance, when observing a moving vehicle from an external reference frame, it appears to be in motion, while from an internal frame within the vehicle, the surroundings may seem stationary.

Scalars and Vectors

1. Scalars

Physical quantities can be described completely by their magnitude only but no particular direction.

Examples- Distance, speed, work, charges, temperature, etc.

Tips for scalars-

• Scalar quantities can be positive, negative or zero.

• Represented by alphabet only A, B, C.

• These physical quantities follow normal algebraic rules of addition.

2. Vectors

Physical quantities can be described by their magnitude and direction.

Physical quantities like Displacement, force, velocity etc. are vectors.

Tips of vectors-

• Vectors can be positive, negative or zero.

• Represented by alphabet having an arrow on their head.

Motion Along a Straight Line

A straight-line motion can be effectively described using only the X-axis of a coordinate system. One-dimensional motion is the movement of a body in a straight line that occurs when only one coordinate of the body's position changes with time.Examples of one-dimensional motion include the motion of a car on a straight road and the motion of a freely falling body.

Path Length (Distance) Vs. Displacement

Path Length: The distance between two points along a route, a scalar quantity that represents the total length travelled.

Displacement: The change in position of a body, often denoted by ∆x = (x₂ - x₁), and it is a vector quantity indicating the overall change in position.

In short, path length considers the total distance travelled, whereas displacement considers the net change in position from the initial to the final point while taking direction into account.

• The magnitude of displacement may or may not be equal to the length of the path.

• When an object returns to its original position along a path with a non-zero length, displacement can be zero. Displacement takes into account the change in position regardless of the total distance travelled, as well as the direction of motion.

Speed and Velocity

Speed

Speed is defined as the rate of distance covered with time. Here are some characteristics of speed:

• It is a scalar quantity denoted by the symbol v.
• Dimension: [M^oL¹T^-1]
• Unit: Meter/second (S.I.), cm/second (C.G.S.)

Types of speed

(a) Uniform speed: A particle moves at uniform speed when it covers equal distances in equal intervals of time, regardless of how small those intervals are. For example, a car travels an equal distance of 5 metres per second, indicating a uniform speed of 5 m/s. Uniform speed denotes a constant rate of motion with no acceleration or deceleration during the time intervals specified.

(b) Non-uniform (variable) speed: A particle with non-uniform (variable) speed travels unequal distances in equal time intervals. For example, a car travels 5m in the first second, 8m in the second second, 10m in the third second, 4m in the fourth second, and so on. This variation in distance covered indicates that the particle's speed varies for each one-second interval, confirming that it moves at a variable speed. Variable speed denotes that the rate of motion varies over time.

(c) Average speed: The average speed (V_avg) of a particle for a given interval of time is defined as the ratio of the total distance travelled (d) to the total time taken (t).

$v_{\text{avg }}=\frac{\text{ Distance traveled }}{\text{ Time taken }}=\frac{d}{t}$

(d) Instantaneous speed: It is the speed of a particle at a specific point in time. When we talk about "speed," we usually mean instantaneous speed.

$$\text{ Instantaneous speed }v=\underset{\mathrm{\Delta }t\to 0}{lim}\frac{\mathrm{\Delta }s}{\mathrm{\Delta }t}=\frac{ds}{dt}$$

Velocity

Velocity is defined as the rate of change of position or the rate of displacement with time.

• It is a vector quantity having the symbol v.
• Dimension of velocity: [M⁰L¹T^-1]
• Unit: Meter/second (S.I.), cm/second (C.G.S.)

Types of Velocity

(1) Uniform velocity: The condition in which both the magnitude and direction of an object's velocity remain constant is referred to as uniform velocity. This occurs when the particle continues to move in the same straight line without changing direction. To put it another way, a particle with uniform velocity must travel at a constant speed along a straight path with no change in motion.

(2) Non-uniform velocity: Changes in the magnitude or direction of the velocity, or both, characterise non-uniform velocity. The particle's speed and/or direction of motion may change in this scenario. Non-uniform velocity indicates that the object is not moving in a straight line at a constant speed, but rather has variations in its motion over time.

(c) Average velocity: It is defined as the ratio of the body's displacement to the time it takes.

$$\text{ Averagevelocity }=\frac{\text{ Displacement }}{\text{ Time taken }};{\overrightarrow{v}}_{av}=\frac{\mathrm{\Delta }\overrightarrow{r}}{\mathrm{\Delta }t}$$

(d) Instantaneous velocity: Instantaneous velocity is defined as the rate of change of the position vector of a particle with respect to time at a specific instant.

$$\text{ Instantaneous velocity }\overrightarrow{v}=\underset{t\to 0}{lim}\frac{\mathrm{\Delta }\overrightarrow{r}}{\mathrm{\Delta }t}=\frac{d\overrightarrow{r}}{dt}$$

Acceleration

Acceleration is defined as the time rate at which an object's velocity changes. it tells us how quickly and in which direction an object's velocity is changing. It is expressed in acceleration units such as metres per second squared.

• It is a vector quantity with the same direction as the change in velocity (not the velocity itself).
• Dimension of acceleration: [M⁰L¹T^-2]
• Units: [meter(m)/second²(s²)] in (S.I. ), [centimeter(cm)/second²(s²)] in (C.G.S.).

Types of Acceleration

(a) Uniform acceleration: Uniform acceleration refers to a situation in which both the magnitude and direction of the acceleration of a body remain constant during its motion.

(b) Non-uniform acceleration: A body is said to have non-uniform acceleration if there are changes in either the magnitude or direction of acceleration, or both, during its motion.

(c) Average acceleration: The average acceleration of an object is defined as the change in velocity per unit time.

${\overrightarrow{a}}_{av}=\frac{\mathrm{\Delta }\overrightarrow{v}}{\mathrm{\Delta }\overrightarrow{t}}=\frac{{\overrightarrow{v}}_2-{\overrightarrow{v}}_1}{\mathrm{\Delta }t}$

Position-Time, Velocity-Time, and Acceleration-Time Graph

PT Graph

VT Graph

Kinematic Equations for Uniformly Accelerated Motion

There are three kinematic equations of rectilinear motion for a constant acceleration.

Relative Velocity

It is defined as the velocity of an object relative to some other object which might be stationary, moving slowly, moving with the same velocity, moving with higher velocity or moving in opposite direction.

If the initial position of two objects A and B are X_A(0) and X_B(0), the position at time t will be,

X_A(t)= X_A(0)+V_At

X_B(t)= X_B(0)+V_Bt

Displacement from object A to B, [X_B(0)-X_A(0)]+(V_B-V_A)

Velocity of B relative to A = V_BA=V_B-V_A

Velocity of A relative to B =V_AB=V_A-V_B

Importance of NCERT Class 11 Physics Chapter 2 Notes

Having a solid understanding of fundamental concepts is essential for success in physics. For reviewing and understanding the key concepts in Motion in a Straight Line, the Class 11 Physics Chapter 2 notes are a great resource. The most recent CBSE Class 11 Physics Syllabus is followed in these notes, which are essential for passing competitive tests like VITEEE, BITSAT, JEE Main, and NEET as well as CBSE school exams.

These notes are accessible in PDF format, which makes it easier for students to study offline and interact with the content whenever it is most convenient for them. By offering a thorough breakdown of fundamental topics including displacement, velocity, acceleration, and equations of motion, they improve comprehension and memory of key concepts.

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