9th Class Science Notes in English chapter 8 Motion
CBSE Revision Notes for CBSE Class 09 Science Motion Motion: Distance and displacement, velocity; uniform and non-uniform motion along a straight line; acceleration, distance-time and velocity-time graphs for uniform motion and uniformly accelerated motion, derivation of equations of motion by graphical method; elementary idea of uniform circular motion.
Class 9th Science chapter 8 Motion Notes in English.
📚 Chapter - 8 📚
👉 Motion 👈
✳️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 change continuously with reference to a point.
✳️Motion Along a Straight Line:-
🔹 When an object moves along a straight line, the motion of the object is called rectilinear motion. For example; motion of a car on highway.
✳️Scalar Quantity:-
🔹 It is the physical quantity having own magnitude but no direction
e.g., distance, speed.
✳️Vector Quantity:-
🔹 It is the physical quantity that requires both magnitude and direction
e.g., displacement, velocity.
✳️Distance:-
🔹 The actual path or length travelled by a object during its journey from its initial position to its final position is called the distance.
Distance is a scalar quantity which requires only magnitude but no direction to explain it.
✳️Displacement:-
🔹 It is the minimum distance from initial position to final position.
Displacement is a vector quantity requiring both magnitude and direction for its explanation. It can be zero (when initial point and final point of motion are same)
There are Two types of Motion:-
✳️Uniform motion:-
🔹 When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.
✳️Non-uniform motion:-
🔹 Motions where objects cover unequal distances in equal intervals of time.
🔹 Non-uniform motion is of two types:-
👉 (i) Accelerated Motion:- When motion of a body increases with time.
👉 (ii) De-accelerated Motion:- When motion of a body decreases with time,

✳️Speed:-
🔹 The measurement of distance travelled by a body per unit time is called speed.
👉Speed= Distance travelled / Time taken
👉SI Unit= m/s (meter/second)
🔹 If a body is executing uniform motion, then there will be a constant speed or uniform motion.
🔹 If a body is travelling with non-uniform motion, then the speed will not remain uniform but have different values throughout the motion of such body.
🔹 For non-uniform motion, average speed will describe one single value of speed throughout the motion of the body.
✳️Velocity:-
🔹 It is the speed of a body in given direction.
👉Velocity= Displacement / Time
👉SI Unit of velocity = ms'⁻¹
🔹 Velocity is a vector quantity. Its value changes when either its magnitude or direction changes.
🔹 For non-uniform motion in a given line, average velocity will be calculated in the same way as done in average speed.
👉Average velocity= Total Displacement / Total time
👉Average Velocity= u+v /2
u= Initial Velocity
v= Final Velocity
✳️Acceleration:-
🔹 Acceleration is seen in non-uniform motion and it can be defined as the rate of change of velocity with time.
a = v-u /t
👉SI Unit= ms⁻²
✳️Retardation/Deacceleration:-
🔹 Deaceleration is seen in non-uniform motion during decrease in velocity with time. It has same definition as acceleration.
a'= (v-u)/t
Here, v < u, ‘a’ = negative (-ve).
✳️Graphical representation of motions:-
👉(i) Distance-time graph:-
🔹 For a distance-time graph, time is taken on x-axis and distance is taken on the y-axis.
👉(ii) Velocity-time graph:-
🔹 For a Velocity-time graph, time is taken on x-axis and Velocity is taken on the y-axis.

✳️Equation of motion by graphical methods:-
👉(i) velocity-time relation (v = u + at):-
👉(ii) The equation for position-time relation (S = ut + ½at²):-
👉(iii) Equation for position-velocity relation (v² = u² + 2as):-
✳️Uniform Circular Motion:-
🔹 In such a motion the speed may be same throughout the motion but its velocity is different at each and every point of its motion. Thus, uniform circular motion is an accelerated motion.