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# Short Notes - Motion Class 9 Notes | EduRev

## Class 9: Short Notes - Motion Class 9 Notes | EduRev

The document Short Notes - Motion Class 9 Notes | EduRev is a part of the Class 9 Course Class 9 Science by VP Classes.
All you need of Class 9 at this link: Class 9

• 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. • 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. • Velocity: Velocity is the speed of an object moving in definite direction. S.I. unit is m/s. • Acceleration: Change in the velocity of an object per unit time. • 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.] • (ii) Velocity-time graph • Equations of motion by graphical method
(i) Equation for Velocity-time Relation:   (ii) Equation for Position-time Relation: 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) Substituting OA = u, OC = AD = t and BD = at (from equation 2) (iii) Equation for Position–Velocity Relation:   • 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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