9th Class Science Notes in English chapter 8 Motion

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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 👈

9th Class Science 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)

9th Class Science Notes in English chapter 8 Motion


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.

9th Class Science Notes in English chapter 8 Motion



✳️Non-uniform motion:-

🔹 Motions where objects cover unequal distances in equal intervals of time.


9th Class Science Notes in English chapter 8 Motion


🔹 Non-uniform motion is of two types:-

👉 (i) Accelerated Motion:- When motion of a body increases with time. 

9th Class Science Notes in English chapter 8 Motion


👉 (ii) De-accelerated Motion:- When motion of a body decreases with time,
9th Class Science Notes in English chapter 8 Motion


✳️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. 
9th Class Science Notes in English chapter 8 Motion

👉Average Speed= Total Distance / Total time


✳️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 
9th Class Science Notes in English chapter 8 Motion
🔹 For uniformly changing velocity, the average velocity can be calculated 
9th Class Science Notes in English chapter 8 Motion

👉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. 
9th Class Science Notes in English chapter 8 Motion
👉Acceleration= Change in velocity/Change in 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. 
9th Class Science Notes in English chapter 8 Motion
👉Deaceleration= Change in velocity/Change in Time 

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.

9th Class Science Notes in English chapter 8 Motion


👉(ii) Velocity-time graph:-

🔹 For a Velocity-time graph, time is taken on x-axis and Velocity is taken on the y-axis.
9th Class Science Notes in English chapter 8 Motion


✳️Equation of motion by graphical methods:-

👉(i) velocity-time relation (v = u + at):-

9th Class Science Notes in English chapter 8 Motion
9th Class Science Notes in English chapter 8 Motion
9th Class Science Notes in English chapter 8 Motion


👉(ii) The equation for position-time relation (S = ut + ½at²):-
9th Class Science Notes in English chapter 8 Motion
9th Class Science Notes in English chapter 8 Motion

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

9th Class Science Notes in English chapter 8 Motion
9th Class Science Notes in English chapter 8 Motion

✳️Uniform Circular Motion:-

9th Class Science Notes in English chapter 8 Motion
🔹 If a body is moving in a circular path with uniform speed, then it is said to be executing 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.

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