Page 113 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

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12 Motion & Time

Chapter in a Nutshell

v An object is said to be in motion if it changes its position over time with respect to stationary
objects around it.
v Motion is of following types–

(a) Rectilinear motion (b) Curvilinear motion.
(c) Circular motion (d) Periodic motion.

v The object that covers a longer distance in a given time interval is declared to be moving
faster than the other object.

v The actual length of the path covered by a moving body is called distance.
v The shortest possible distance covered by a body between its initial and final positions is

called displacement.
v The SI unit for both distance & displacement is metre (m).
v Speed is defined as the distance covered by a moving object in a unit time.

Speed = Distance covered
Time taken
v The units commonly used for speed are m/s (metre/second ) or km/h (kilometre/hour).

v A body is said to be in uniform motion if it travels equal distances in equal intervals of time.
v A body is said to be in a non-uniform motion if it travels unequal distances in equal intervals

of time.

v The device which records speed of vehicles in km/h is called a speedometer. The device
which records the distance covered by a vechicle in kilometres is called an odometer.

v Our ancestors kept track of time by observing the length & direction of shadows.
v 1 day = Time between one sunrise & the next sunrise

= 24 hours.
v 1 Month = Time between two new moons.

= 30 or 31 days.

v 1 year = Time Earth takes to complete its one revolution around the Sun
= 365 days or 366 days (in a leap year)

v February is the only month which has 28 days or 29 days (in a leap year).
v Ancient time-measuring devices were–sundial, sand clock, etc.

v Modern time-measuring devices are wall clock, wristwatch, etc.
v Clocks use the concept of periodic motion. Earlier, clocks were based on a simple pendulum.

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