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.
π Chapter - 8 π
π Motion π

✳️Rest:-
πΉ A body is said to be in a state of rest when its position does not change with respect to a reference point.
✳️Motion:-
πΉ 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:-
πΉ 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:-
πΉ It is the physical quantity having own magnitude but no direction
e.g., distance, speed.
✳️Vector Quantity:-
πΉ It is the physical quantity that requires both magnitude and direction
e.g., displacement, velocity.
✳️Distance:-
πΉ 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:-
πΉ 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:-
πΉ When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.

✳️Non-uniform motion:-
πΉ Motions where objects cover unequal distances in equal intervals of time.

πΉ Non-uniform motion is of two types:-
π (i) Accelerated Motion:- When motion of a body increases with time.

π (ii) De-accelerated Motion:- When motion of a body decreases with time,



✳️Speed:-
πΉ The measurement of distance travelled by a body per unit time is called speed.
πSpeed= Distance travelled / Time taken
πSI Unit= m/s (meter/second)
πΉ If a body is executing uniform motion, then there will be a constant speed or uniform motion.
πΉ 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.
πΉ For non-uniform motion, average speed will describe one single value of speed throughout the motion of the body.

✳️Velocity:-
πΉ It is the speed of a body in given direction.
πVelocity= Displacement / Time
πSI Unit of velocity = ms'⁻¹
πΉ Velocity is a vector quantity. Its value changes when either its magnitude or direction changes.
πΉ For non-uniform motion in a given line, average velocity will be calculated in the same way as done in average speed.
πAverage velocity= Total Displacement / Total time


πAverage Velocity= u+v /2
u= Initial Velocity
v= Final Velocity
✳️Acceleration:-
πΉ 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
πSI Unit= ms⁻²
✳️Retardation/Deacceleration:-
πΉ 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:-
π(i) Distance-time graph:-
πΉ For a distance-time graph, time is taken on x-axis and distance is taken on the y-axis.

π(ii) Velocity-time graph:-
πΉ 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:-
π(i) velocity-time relation (v = u + at):-



π(ii) The equation for position-time relation (S = ut + ½at²):-


π(iii) Equation for position-velocity relation (v² = u² + 2as):-


✳️Uniform Circular Motion:-

πΉ 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.
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