CBSE CLASS IX, MOTION, PHYSICS NOTES PART I

 

CBSE CLASS 12, MOTION, PHYSICS NOTES-(PART I)

MOTION

According to the CBSE Syllabus 2025-26

CBSE Class 9 Science Chapter 8 Motion Notes

In Class 9 Science Chapter 8 Motion, students learn to describe the motion of objects along a straight line and express such motions through simple equations and graphs. The chapter also discusses ways of describing circular motion.

TOPICS IN THE CHAPTER

• Introduction

• Distance and Displacement

• Uniform and Non-uniform motion

• Speed

• Velocity

• Accelerated and Decelerated motion

• Equations of motion

• Graphical representation of motion

• Uniform circular motion

INTRODUCTION

REST:

A body is said to be in a state of rest when its position does not change with respect to a reference point.

 MOTION:

A body is said to be in a state of motion when its position changes continuously with reference to a point.

UNDERSTANDING MOTION

Motion can be of different types depending on the kind of path by which the object is moving.

(i) Circulatory motion / Circular motion – In a circular path.

(ii) Linear motion – In a straight line path.

(iii) Oscillatory/Vibratory motion – To and fro path with respect to the origin.

REFERENCE POINT AND REFERENCE FRAME

To describe the position of an object, we need a reference point or origin. An object may seem to be moving to one observer and stationary to another.

Example: A passenger inside a bus sees the other passengers at rest, whereas an observer outside the bus sees the passengers to be in motion.

In order to make observations easy, a convention or a common reference point or frame is needed. All objects must be in the same reference frame.

DISTANCE AND DISPLACEMENT

DISTANCE

The actual path or length travelled by an object during its journey from its initial position to its final position is called the distance. Distance is a scalar quantity that requires only magnitude but no direction.

DISPLACEMENT                                                        

Displacement is the shortest distance between two points or the distance between the starting and final positions with respect to time. It has magnitude as well as direction. Displacement can be zero, but distance cannot. Displacement is a vector quantity requiring both magnitude and direction for its explanation. Displacement can be zero (when the initial point and final point of motion are the same). Example: circular motion.

DIFFERENCE BETWEEN DISTANCE AND

 DISPLACEMENT

 

DISTANCE	DISPLACEMENT
Length of the actual path travelled by an object.	The shortest length between the initial point and the farthest point of an object.
It is a scalar quantity.	It is a vector quantity.
It remains positive, can’t be ‘0’ or negative.	It can be positive (+ve), negative (-ve), or zero.
Distance can be equal to displacement (in a linear path).	Displacement can be equal to distance or it’s lesser than distance.

MAGNITUDE

Magnitude is the size or extent of a physical quantity. In physics, we have scalar and vector quantities.

SCALAR QUANTITIES

Physical quantities have their own magnitude but no direction. Example: distance, speed. time,  distance, mass, temperature, area, volume.

VECTOR QUANTITIES

Vector quantities are expressed in magnitude as well as direction of the object. E.g.: Velocity, displacement, weight, momentum, force, acceleration, etc. Time, Average Speed, and Velocity.

TIME AND SPEED

TIME

Time is the duration of an event that is expressed in seconds. Most physical phenomena occur with respect to time. It is a scalar quantity.

• Speed, Velocity, Accelerated, and Decelerated motion, Equations of motion, Graphical representation of motion, Uniform circular motion will be covered in the next blog............... MOTION PART II.