Summary of chapter motion class 9 .
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Answer:
movement of any object from one position with respect to the observer is called motion
What is motion?
If the location of an object changes with time the object is said to be in motion.
Motion in a Straight Line
Distance – The distance covered by an object is described as the total path length covered by an object between two endpoints.
Distance is a numerical quantity. We do not mention the direction in which an object is travelling while mentioning about the distance covered by that object.
According to the figure 1 given above, if an object moves from point O to point A then total distance travelled by the object is given as 60 km.
Displacement – The shortest possible distance between the initial and final position of an object is called Displacement.
Consider the figure 1 given above, here the shortest distance between O and A is 60 km only. Hence, displacement is 60 km.
Displacement depends upon the direction in which the object is travelling.
Displacement is denoted by Δx.
Zero Displacement – When the first and last positions of an object are same, the displacement is zero.
For Example, consider the diagrams given below.
Displacement at point A = 0 because the shortest distance from A to A is zero.
Here, displacement of object B is negative
ΔB = Bf − B0 = 7–12 = – 5
A negative sign indicates opposite direction here.
Also, displacement of object A is positive
ΔA = Af − A0 = 7– 0 = 7
What are Scalar and Vector Quantities?
A scalar quantity describes a magnitude or a numerical value.
A vector quantity describes the magnitude as well as the direction.
Hence, distance is a scalar quantity wh