Class 7 Science Chapter 8: Measurement of Time and Motion (Hinglish Notes)

Ye chapter kis baare mein hai?

Prerna ek tez dhaavika hai. Wo dekhti hai ki Olympic ki timing tab bhi winner chun leti hai jab do runners ek saath line paar karte lagte hain, jabki uske school mein stopwatch chalti hai, maa haath ki ghadi pehenti hain, behen phone dekhti hai, aur chacha ke paas Braille ghadi aur bolne waali ghadi hai. Isse wo sochti hai ki clock se pehle log time kaise naapte the. Chapter isi sawaal ko sundial se atomic clock tak le jaata hai, simple pendulum ko samajhta hai, aur phir time se gati naapta hai: kaun tez hai, speed kya hai, aur uniform aur non-uniform motion mein kya fark hai.

Puraane zamaane mein time naapna

Logon ne dekha ki prakriti ki kai ghatnaayein tay samay ke baad dohraati hain: sooryoday aur suryast, Chaand ki kalaayein, mausam. In chakron se calendar bane, aur din Sooraj se tay hua. Din ke andar chhota time naapne ke liye unhone sundial, water clock, hourglass aur candle clock banaaye.

India mein time naapne ka lamba itihaas hai. Arthashastra mein parchhaai waale clock aur bartan se baahar behte paani ka zikr hai; lagbhag 530 CE mein Varahamihira ne khadi chhadi ki parchhaai se time nikaalne ka niyam diya; aur Aryabhata ne doobne waale katore ka water clock, ghatika-yantra, bataya. Iska katora 24 minute mein bharkar doobta tha, jise ek ghatika kehte the, isliye ek din mein 60 ghati hoti thi, aur har baar katora doobne pe nagaade, shankh ya ghanta bajaakar bataya jaata tha. Jaipur ke Jantar Mantar ka Samrat Yantra, jo lagbhag 300 saal pehle bana, duniya ka sabse bada patthar ka sundial hai: 27 m ooncha, aur iski parchhaai har second lagbhag 1 mm chalti hai.

Pendulum clock se atomic clock tak

Fourteenth century se mechanical clocks wazan, gears aur springs se chalne lage. 1656 mein Christiaan Huygens ne pendulum clock banaaya, Galileo ki is khoj se prerit hokar ki jhoolta lamp har jhoole mein utna hi time leta hai. Har clock, puraana ho ya naya, kisi niyamit roop se dohraane waali prakriya ko ginta hai. Aaj ke clocks quartz crystal ya kuch khaas atoms ke chhote, bahut tez kampan ginte hain. Huygens ke shuruaati clock din mein 10 second aage ya peeche ho sakte the, par atomic clocks laakhon saal mein sirf lagbhag ek second khote hain. Aur padho time kaise naapte hain mein.

Simple pendulum

Simple pendulum ek chhoti dhaatu ki gend, yaani bob, hai jo lambe dhaage se ek mazboot support se latki ho. Ruka hua wo apni mean position pe latakta hai. Ek taraf kheenchkar chhodne pe wo periodic motion mein jhoolta hai. Ek oscillation O se extreme position A, phir doosri extreme position B, aur waapas O tak ka safar hai. Ek oscillation ka time time period hai.

Ise naapne ke liye lagbhag 100 cm lambe pendulum ke 10 oscillations ka time naapo aur 10 se bhaag do; baar-baar naapne pe lagbhag wahi jawab aata hai. Lambe pendulum ka time period lamba hota hai, par bob ka mass badalne se koi fark nahi padta. Ek jagah pe ek jaisi lambai ke saare pendulums ka time period ek jaisa hota hai, isiliye pendulum time rakh sakte hain. Padho simple pendulum kya hai.

Time ki units

Time ki SI unit second hai, jiska nishaan s hai. Badi units minute (min) aur hour (h) hain: 60 s = 1 min aur 60 min = 1 h. Unit ke naam aur nishaan chhote aksharon mein aur ekvachan mein likhe jaate hain, number ke baad space ke saath aur nishaan ke baad full stop ke bina: 5 s, 5 sec nahi. Seconds ki suyi waala deewaar ka clock 1 second jitna chhota antar naap sakta hai, par race ki timing second ke sauvein ya hazaarvein hisse tak naapti hai, heart monitor milliseconds naapte hain, aur computer microseconds mein kaam karte hain.

Dheere ya tez? Speed

Ek hi doori ki race mein jo runner ek jaise samay mein zyaada doori tay kare, wo tez hai. Alag-alag dooriyon ki tulna ke liye hum speed istemaal karte hain: ek unit time mein tay ki gayi doori.

Speed = kul tay doori ÷ kul laga time. SI unit metre per second (m/s) hai; kilometre per hour (km/h) bhi aam hai. Swati 15 min mein 3.6 km cycle chalaakar school jaati hai: 3600 m ÷ 900 s = 4 m/s. Formula ko palatne pe, doori = speed × time (50 km/h pe 2 h chalne waali bus 100 km jaati hai) aur time = doori ÷ speed (90 km/h pe 360 km mein 4 h lagte hain). Kyunki cheezein raaste mein tez aur dheere hoti hain, ye asal mein average speed hai. Gaadi ka speedometer us pal ki speed dikhata hai, aur odometer kul tay doori. Dekho speed aur uniform motion.

Uniform aur non-uniform motion

Seedhi line pe gati linear motion hai. Station A se nikalti train tez hoti hai, B se C tak constant speed se chalti hai, phir dheemi hokar D pe ruk jaati hai. B aur C ke beech uski gati uniform linear motion hai: wo barabar samay mein barabar doori tay karti hai. A se B aur C se D uski gati non-uniform hai, kyunki speed badalti rehti hai. Book ki table mein train X har 10 minute mein 20 km chalti hai (uniform), jabki train Y alag-alag doori chalti hai (non-uniform). Poori tarah uniform motion ek aadarsh sthiti hai, isiliye hum average speed istemaal karte hain. Saare sawaalon ke jawab Chapter 8 ke NCERT solutions mein hain.