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Political Science NCERT Solutions Class 9 Science Chapter 7 – Motion
Class 9 Science
Last Updated: 23 July 2026
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Tough Words (Glossary)
motion
Meaning: change in position with time
अर्थ: समय के साथ स्थिति में परिवर्तन
"The motion of the train was smooth."
stationary
Meaning: not moving
अर्थ: स्थिर / अचल
"The tree is stationary but the bus moves."
perceive
Meaning: to notice or become aware of
अर्थ: अनुभव करना / पहचानना
"We perceive wind by seeing leaves move."
infer
Meaning: to conclude from evidence
अर्थ: अनुमान लगाना
"We infer air’s motion from flying dust."
reference point
Meaning: a fixed point used to describe position
अर्थ: संदर्भ बिंदु
"The station is our reference point for the school’s location."
origin
Meaning: chosen reference point
अर्थ: आधार बिंदु / मूल
"Take O as the origin on the diagram."
displacement
Meaning: shortest straight-line distance from initial to final position with direction
अर्थ: आर्म्भिक से अंतिम स्थिति तक का लघुत्तम सीधी दूरी (दिशा सहित)
"The displacement was 35 km east."
distance
Meaning: total path length travelled
अर्थ: कुल पथ लंबाई
"The total distance covered was 95 km."
magnitude
Meaning: numerical value or size of a quantity
अर्थ: परिमाण / मात्रात्मक मान
"The magnitude of displacement is 35 km."
straight line
Meaning: a line with no curves
अर्थ: सीधी रेखा
"The car moved in a straight line."
uniform motion
Meaning: equal distances in equal time intervals
अर्थ: समवेक गति
"A bead shows uniform motion on the belt."
non-uniform motion
Meaning: unequal distances in equal time intervals
अर्थ: असमवेक गति
"Traffic causes non-uniform motion of the car."
speed
Meaning: distance covered per unit time
अर्थ: वेग (दूरी/समय)
"Her speed was 10 m/s."
average speed
Meaning: total distance divided by total time
अर्थ: औसत चाल
"The average speed for the trip was 50 km/h."
velocity
Meaning: speed with direction
अर्थ: वेग (दिशा सहित)
"The car’s velocity was 40 km/h north."
average velocity
Meaning: displacement divided by time
अर्थ: औसत वेग
"Average velocity depends on displacement."
acceleration
Meaning: rate of change of velocity
अर्थ: त्वरण
"The bike has an acceleration of 2 m/s²."
deceleration
Meaning: negative acceleration
अर्थ: ऋणात्मक त्वरण / मंदन
"Brakes cause deceleration."
SI unit
Meaning: international standard unit
अर्थ: अंतर्राष्ट्रीय इकाई (एस.आई.)
"The SI unit of speed is m/s."
metre per second
Meaning: unit of speed or velocity
अर्थ: मीटर प्रति सेकंड
"The sprinter ran at 8 metres per second."
kilometre per hour
Meaning: unit of speed
अर्थ: किलोमीटर प्रति घंटा
"The car moved at 60 kilometres per hour."
graph
Meaning: diagram showing relation between quantities
अर्थ: आरेख / ग्राफ
"We drew a distance–time graph."
distance–time graph
Meaning: graph with distance vs time
अर्थ: दूरी–समय आरेख
"A straight line shows uniform speed."
velocity–time graph
Meaning: graph with velocity vs time
अर्थ: वेग–समय आरेख
"The area under the graph gives displacement."
slope
Meaning: ratio showing steepness of a line
अर्थ: ढाल
"Slope of the distance–time graph gives speed."
area under graph
Meaning: region whose size equals a quantity
अर्थ: ग्राफ के नीचे का क्षेत्रफल
"Area under v–t graph equals distance."
linear
Meaning: forming a straight line
अर्थ: रैखिक / सीधा
"The relation is linear for uniform motion."
nonlinear
Meaning: not forming a straight line
अर्थ: अरैखिक
"Accelerated motion gives a nonlinear curve."
proportional
Meaning: in a constant ratio
अर्थ: समानुपाती
"Distance is proportional to time in uniform speed."
parallel
Meaning: lines with equal separation
अर्थ: समांतर
"A constant velocity gives a line parallel to the time axis."
perpendicular
Meaning: at right angles (90°)
अर्थ: लंबवत
"Draw a perpendicular from B to the x-axis."
initial velocity
Meaning: velocity at the start (u)
अर्थ: प्रारम्भिक वेग (u)
"The initial velocity was 2 m/s."
final velocity
Meaning: velocity at the end (v)
अर्थ: अंतिम वेग (v)
"The final velocity reached 10 m/s."
equations of motion
Meaning: relations between u, v, a, s, t
अर्थ: गति के समीकरण
"We used equations of motion to find distance."
uniform acceleration
Meaning: equal change in velocity per equal time
अर्थ: समवेक त्वरण
"Free fall has uniform acceleration."
non-uniform acceleration
Meaning: unequal change in velocity per equal time
अर्थ: असमवेक त्वरण
"City driving shows non-uniform acceleration."
displacement vector
Meaning: displacement with direction
अर्थ: विस्थापन सदिश
"Displacement is a vector quantity."
scalar quantity
Meaning: quantity with magnitude only
अर्थ: अदिश राशि
"Speed is a scalar quantity."
average
Meaning: mean value over a period
अर्थ: औसत
"Average speed smooths out variations."
instantaneous
Meaning: at a particular moment
अर्थ: क्षणिक
"A speedometer shows instantaneous speed."
uniform circular motion
Meaning: motion in a circle with constant speed
अर्थ: समवेक वृत्तीय गति
"Planets approximate uniform circular motion."
circumference
Meaning: distance around a circle (2πr)
अर्थ: परिधि (2πr)
"He ran one circumference of the track."
radius
Meaning: distance from centre to circle
अर्थ: त्रिज्या
"The radius of the path was 20 m."
tangential
Meaning: along the tangent; at right angle to radius
अर्थ: स्पर्शरेखीय
"On release, the stone flew off tangential to the circle."
accelerated motion
Meaning: motion with changing velocity
अर्थ: त्वरित गति
"A car speeding up has accelerated motion."
trajectory
Meaning: the path followed by a moving object
अर्थ: पथ / प्रक्षेप पथ
"The ball’s trajectory curved."
displacement–time
Meaning: plot of displacement vs time
अर्थ: विस्थापन–समय
"Displacement–time slope gives velocity."
interpret
Meaning: to explain the meaning of
अर्थ: व्याख्या करना / समझना
"Interpret the velocity–time graph."
derive
Meaning: to obtain from given relations
अर्थ: व्युत्पन्न करना
"We derive equations of motion graphically."
average acceleration
Meaning: change in velocity divided by time taken
अर्थ: औसत त्वरण
"Average acceleration was 0.4 m/s²."