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Short Notes - Motion Notes | Study Science Class 9 - Class 9

Document Description: Short Notes - Motion for Class 9 2022 is part of Science Class 9 preparation. The notes and questions for Short Notes - Motion have been prepared according to the Class 9 exam syllabus. Information about Short Notes - Motion covers topics like and Short Notes - Motion Example, for Class 9 2022 Exam. Find important definitions, questions, notes, meanings, examples, exercises and tests below for Short Notes - Motion.

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  • An object is said to be in motion when its position changes with time.
  • We describe the location of an object by specifying a reference point. Motion is relative. The total path covered by an object is said to be the distance travelled by it.
  • The shortest path/distance measured from the initial to the final position of an object is known as the displacement.
    Short Notes - Motion Notes | Study Science Class 9 - Class 9
  • 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.
  • Speed: The distance travelled by an object in unit time is referred to as speed. Its unit is m/s.
  • Average speed: For non-uniform motion, the average speed of an object is obtained by dividing the total distance travelled by an object by the total time taken.

Short Notes - Motion Notes | Study Science Class 9 - Class 9

  • Velocity: Velocity is the speed of an object moving in definite direction. S.I. unit is m/s.

Short Notes - Motion Notes | Study Science Class 9 - Class 9

  • Acceleration: Change in the velocity of an object per unit time.

Short Notes - Motion Notes | Study Science Class 9 - Class 9

  • Graphical representation of motion
    (i) Distance-time graph: For a distance-time graph time is taken on x-axis and distance is taken on y-axis. [Note: All independent quantities are taken along the x-axis and dependent quantities are taken along y-axis.]

Short Notes - Motion Notes | Study Science Class 9 - Class 9

  • (ii) Velocity-time graph

Short Notes - Motion Notes | Study Science Class 9 - Class 9

 

  • Equations of motion by graphical method
    (i) Equation for Velocity-time Relation: 

Short Notes - Motion Notes | Study Science Class 9 - Class 9

Short Notes - Motion Notes | Study Science Class 9 - Class 9

Short Notes - Motion Notes | Study Science Class 9 - Class 9
(ii) Equation for Position-time Relation:

Short Notes - Motion Notes | Study Science Class 9 - Class 9

Let us assume,
s = distance travelled by the object
t = time t
a = uniform acceleration.                  
 ∴ Distance travelled by the object is given by area enclosed with OABC in the graph.                    
∴ s = area OABC (which is a trapezium)
= (area of rectangle OADC) + (area of ∆ABD)

Short Notes - Motion Notes | Study Science Class 9 - Class 9

Substituting OA = u, OC = AD = t and BD = at (from equation 2)  

Short Notes - Motion Notes | Study Science Class 9 - Class 9

(iii) Equation for Position–Velocity Relation:

Short Notes - Motion Notes | Study Science Class 9 - Class 9

Short Notes - Motion Notes | Study Science Class 9 - Class 9

Short Notes - Motion Notes | Study Science Class 9 - Class 9

  • Uniform circular motion: When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.

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