Samay ka Maapan

Class 7 Science · Chapter 8: Samay aur Gati ka Maapan · NCERT Curiosity section 8.1

Seekho

Meher ne school ki 100 m daud jeeti aur ab rajya ke liye daudna chahti. Stadium mein electronic timer second ke sauvein hisse tak naapte, par school mein coach stopwatch use karte. "Ghadiyon se pehle log samay kaise naapte the?" ghar lautte bus mein wo sochti, apna phone, daadi ki kalaai ghadi aur chaacha ki bolne wali ghadi dekhte hue.

Logon ne dekha prakriti dohraati hai: sooryoday-sooryaast, Chaand ki kalaayein, mausam. Inse din aur calendar bane. Din baantne ke liye unhone banaaye dhoop ghadi (chalti chhaaya), jal ghadi (bartan se bahar ya andar behta paani), ret ghadi (girti ret) aur mombatti ghadi (nishaan wali mombatti). Jaipur ke Jantar Mantar ka vishaal Samrat Yantra, 27 m ooncha, lagbhag 2 second tak samay padh sakta!

Praacheen Bharat mein Ghatika-yantra paani par tairta chhote chhed wala katora tha; ye 24 minute (ek ghati) mein bharkar doobta, to din mein 60 ghati. Har baar doobne par dhol ya ghanta bajta. Baad mein giyar aur spring aaye, aur 1656 mein Huygens ki pendulum ghadi, Galileo se prerit, jinhone jhoolte lamp ka samay apni nabz se naapa tha.

Saral pendulum dhaage se majboot aadhaar par latka chhota bob hai. Madhya sthiti O se wo ek chhor A, phir doosre chhor B, aur waapas O: ek dolan. Ek dolan ka samay aavartkaal. 10 dolan naapo aur 10 se bhaag do. Ek lambaai ke liye aavartkaal wahi rehta; ye lambaai par nirbhar, bob ke dravyamaan par nahi.

Saari ghadiyan barabar antaraal par dohraati cheez use karti: quartz ghadi crystal ke chhote tez kampan, aur parmaanu ghadi parmaanu, jo laakhon saal mein lagbhag ek second khoti. Samay ki SI ikaai second (s); 60 s = 1 min aur 60 min = 1 h. "15 min" ya "2 h" likho, kabhi "15 mins." ya "2 hrs" nahi.

Explore: pendulum ka aavartkaal kaun tay karta?

1. Har pendulum naapkar sort karo.

Explore: ghadiyon ki kahaani.

1. Kadam kram mein lagao.

Yaad rakho

• Shuruaati ghadiyan chhaaya, paani, ret aur mombatti use karti; Ghatika-yantra 24 minute ki ghati naapta.
• Pendulum ka aavartkaal lambaai par nirbhar, bob par nahi; samay ki SI ikaai second.

Quick check

Pendulum 15 s mein 10 dolan karta. Aavartkaal?

1. 1.5 s
2. 15 s
3. 10 s
4. 150 s

Socho

Park ka jhoola chhota bachcha baithe ya bada, aavartkaal wahi. Kyun?

Practice

Teen levels (easy, medium, hard) ke naye sawaalon se practice karo, kuch hands-on, hints aur hal ke saath. Topic poora karne ke liye pichhle 5 mein se 4 sahi karo.