How Forces Affect Motion (Forces Motion par Kaise Asar Daalte Hain): Class 9 Science Chapter 6 Hinglish mein

Exploration · Hinglish notes, simulations aur practice · Official NCERT chapter PDF ↗

Published 13 Oct 2026 · Updated 13 Oct 2026

95 min
1 simulation
30 practice questions
23 MCQs

Is chapter mein aap kya seekhenge

Force ko magnitude aur direction wale push ya pull ki tarah samjhao, aur spring balance se use newtons mein naapo
Jab forces ek hi line mein lagte hain to net force nikaalo, aur balanced aur unbalanced forces mein fark pehchano
Samjhao ki friction sliding ka virodh kaise karta hai aur contact wali surfaces par kaise depend karta hai, aur kisi object par weight aur normal force pehchano
Newton's first law batao, use inertia se jodo, aur zero net force ke liye position–time aur velocity–time graphs banao
Problems solve karne ke liye F = ma aur F = mg ko equations of motion ke saath use karo, aur samjhao ki zyada stopping time ka matlab kam force kyun hota hai
Newton's third law batao, alag-alag objects par lagne wale pair ke dono forces pehchano, aur chalna, naav chalana, recoil aur rockets samjhao
Jude hue objects ko ek system maano aur sirf external force se uska acceleration nikaalo

NCERT Science Class 9, Chapter 6, pp. 94–115 par based original companion text. Yeh NCERT se juda nahi hai aur NCERT ne ise endorse nahi kiya hai.

Chapter 4 mein tumne motion ko position, velocity aur acceleration se describe kiya, lekin yeh kabhi nahi poocha ki kisi object ko chalne, rukne, tez hone ya mudne ke liye kaun majboor karta hai. Bicycle ko slope par bina pedal maare chhod do, to woh apne aap speed pakad leti hai. Seedhi road par woh dheere-dheere speed khokar ruk jaati hai. Handle ghumao to uski direction badal jaati hai. Har baar kuch na kuch us par act kar raha hai.

Woh kuch hai ek force. Is chapter mein hum forces ko dhyaan se dekhenge, samjhenge ki kai forces milkar kaise kaam karte hain, aur un teen laws of motion se milenge jinse Isaac Newton ne force ko motion se joda.

6.1 Force ka Concept

Pichhli classes mein tumne force ko push ya pull ki tarah jaana tha. Force kisi object ke saath chaar tarah ke kaam kar sakta hai. Woh ruke hue object ko chala sakta hai, uski speed badal sakta hai, uski direction badal sakta hai, ya uski shape badal sakta hai. Carrom striker ko flick karo aur ruki hui goti tez nikal jaati hai. Bicycle ke brakes dabao aur woh dheemi ho jaati hai. Goalkeeper ki hatheli football ko naye angle par bhej deti hai. Belan aate ki loi ko chapta karke roti bana deta hai. Fig. 6.1 ek hi rubber ball par chaaron effects dikhata hai.

3/4Side se push uski motion ki direction badal deta hai.

Fig. 6.1Force motion shuru kar sakta hai, speed badal sakta hai, direction badal sakta hai ya shape badal sakta hai.NCERT Fig. 6.1 · p. 94

Floor par rakhi ek rubber ball upar se dekhi hui, chaar steps mein. Step 1: ball ruki hui hai aur left se ek push use right ki taraf chala deta hai. Step 2: peechhe se doosra push chalti ball ko aur tez kar deta hai, jo lambe velocity arrow se dikhaya gaya hai. Step 3: side se ek push ball ko mod deta hai, isliye uska velocity arrow ab tirchha neeche aur right ki taraf point karta hai. Step 4: do hatheliyan ball ko dono taraf se dabati hain aur woh ek lamba oval ban jaati hai.

Maan lo ek dost kehta hai, 'Maine box ko 50 N se push kiya.' Kya tum bata sakte ho box kahan gaya? Abhi nahi: tumhe yeh bhi jaanna hoga ki push kis taraf tha. Tumhare jaane hue har force mein ek direction shaamil hoti hai. Earth ka pull neeche ki taraf hota hai. Paani tairti bottle ko upar push karta hai. Friction hamesha sliding ke ulta point karta hai. Isliye force poori tarah tabhi describe hota hai jab uski magnitude (woh kitna strong hai) aur uski direction dono batayi jaayein, bilkul Chapter 4 ke displacement, velocity aur acceleration ki tarah.

Definition

Force

Kisi object par lagne wala push ya pull jo kisi doosre object ke saath uske interaction se aata hai. Force ki magnitude aur direction hoti hai; uski SI unit newton (N) hai.

ExampleGirte hue aam par Earth ka pull: lagbhag 5 N, Earth ke centre ki taraf.

Forces ko newtons (symbol N) mein naapa jaata hai, yeh SI unit Isaac Newton ke naam par hai. Poora likhne par unit chhote letter se shuru hoti hai: newton, Newton nahi.

6.1.1 Force ki magnitude naapna

Koi push ya pull kitna strong hai? Ise naapne ke liye hum spring balance use karte hain. Uske hook ko kheencho to andar ki spring khinch jaati hai: jitna zyada pull, utna lamba khinchaav. Newtons mein marked scale par chalta pointer batata hai ki pull kitna strong hai. Hook se sabziyon ka thaila latkao, to jo pull naapa ja raha hai woh thaile par Earth ka pull hai, yaani uska weight. Iski jagah hook ko apne haath, rubber band ya toy car se kheencho, to balance us pull ko bhi waise hi padh leta hai (Fig. 6.2).

2/3Earth thaile ko 4.9 N se neeche kheenchti hai, yahi uska weight hai.

Fig. 6.2Spring balance kisi object ka weight, ya apne hook par laga koi bhi doosra pull padhta hai.NCERT Fig. 6.2 · p. 95

Ek vertical spring balance jiske scale par 0 N, 5 N aur 10 N marked hain. Step 1: hook se kuch nahi latka, spring chhoti hai aur pointer 0 N padhta hai. Step 2: hook se 500 g dal ka kapde ka thaila latka hai, spring khinch jaati hai aur pointer 4.9 N padhta hai, jo dal ka weight hai. Step 3: thaile ki jagah ek haath hook ko neeche kheenchta hai aur pointer aur aage, 8 N tak jaata hai.

Quick check

3 mein se 1

Ek batter tez ball ko seedha bowler ke paas se wapas maarta hai. Bat ka force mainly kis effect ka example hai?

Ball ki shape badalnaMotion ki direction badalnaRuki hui ball ko chalanaBall ko hamesha ke liye rok dena

Answer dekho

Answer (B) Motion ki direction badalna

Ball pehle se batter ki taraf aa rahi thi; bat use ulti taraf bhej deta hai, isliye uski motion ki direction badalti hai. Ball ek pal ke liye thoda pichakti zaroor hai, lekin woh main effect nahi hai.

6.2 Balanced aur Unbalanced Forces

Stand par khadi ek bicycle dekho. Earth use neeche kheenchti hai, phir bhi woh zameen mein nahi dhansti, kyunki zameen uske tyres aur stand ko upar push karti hai. Us par ek saath do forces lagte hain, aur woh ek doosre ko cancel kar dete hain. Tumhare aas-paas ke zyaadatar objects aise hi hain, jin par ek saath kai forces lagte hain. To phir kya tay karta hai ki aisa object kaise chalega?

Ek supermarket trolley socho jise ek dost aage se aur doosra peechhe se push kar raha hai. Agar dono barabar zor lagayein, to trolley wahin rehti hai. Do forces jo size mein barabar par direction mein ulte hon, ek doosre ko cancel kar dete hain: yeh balanced forces (संतुलित बल) hain. Agar ek dost zyada zor se push kare, to forces unbalanced ho jaate hain, aur trolley us taraf lurhakti hai jidhar bada push point karta hai (Fig. 6.3).

2/320 N ke against 30 N: unbalanced, bade push ki taraf 10 N net force.

Fig. 6.3Ulte forces ghatte hain, ek hi direction ke forces judte hain.NCERT Fig. 6.4 · p. 96

Floor par ek trolley jiske force arrows scale ke hisaab se bane hain. Step 1: left se 20 N ka push aur right se 20 N ka push; net force zero hai aur trolley nahi hilti. Step 2: left se 30 N aur right se 20 N; net force right ki taraf 10 N hai aur trolley right chalti hai. Step 3: 30 N aur 20 N dono left se push karte hain; forces judkar right ki taraf 50 N ka net force banate hain aur trolley aur aage jaati hai.

Woh akela force jiska effect saare forces ke milkar lagne jaisa hi ho, net force (परिणामी बल) kehlata hai. Ek seedhi line mein lagne wale forces ke liye do cases hain. Jab do forces ulti directions mein lagte hain, to net force unki magnitudes ke difference ke barabar hota hai aur bade force ki taraf point karta hai. Jab woh ek hi direction mein lagte hain, to net force unka sum hota hai. Socho ek insaan bhare hue thele ko aage se kheench raha hai aur doosra peechhe se push kar raha hai: unki mehnat jud jaati hai.

Definition

Net force

Woh akela force jiska effect object par lagne wale saare forces ke milkar lagne jaisa hi ho. Ek line mein: ek taraf point karne wale forces jodo aur doosri taraf wale ghatao.

Example18 N east aur 12 N west ke pulls milkar 6 N east ka net force dete hain.

Definition

Balanced forces

Kisi object par lagne wale woh forces jinka net force zero ho. Yeh object ki rest ya motion ki state ko nahi badalte.

ExampleDo dost trolley ko ulte siron se 20 N-20 N se push kar rahe hain.

Example 6.1NCERT Example 6.1 · p. 96

Do bachche, books ka ek carton

Meera books ke ek carton ko $18 N$ ke force se kheenchti hai. Kabir usi carton par $12 N$ lagata hai. Floor bahut smooth hai, isliye friction ko ignore karo. Net force ki magnitude aur direction nikaalo jab:

(a) dono forces east ki taraf lagte hain;
(b) Meera east ki taraf kheenchti hai aur Kabir west ki taraf;
(c) Meera west ki taraf kheenchti hai aur Kabir east ki taraf.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Practice · 2 questions

Ruko aur socho 1–2: answers ke saath

1
Short answerEasyNCERT Pause and Ponder Q1
Ek gamla chain se chhat ke hook par latka hai aur hilta nahi.
1. Gamle par lagne wale do forces ke naam batao.
  Solution dikhao
  Earth gamle ko neeche kheenchti hai (uska weight). Chain gamle ko upar kheenchti hai (chain mein tension).
2. Kya yeh forces balanced hain? Tumhe kaise pata?
  Solution dikhao
  Haan. Gamla rest mein rehta hai, isliye us par net force zero hona chahiye: chain ka upar wala pull gamle ke weight ke barabar hai.
2
Short answerMediumNCERT Pause and Ponder Q2
Ravi aur uska dost ek lakdi ke stool ko ulti taraf se push karte hain. Stool Ravi ki taraf sarakne lagta hai.
1. Kya stool par forces balanced hain?
  Haan, balancedNahi, unbalanced
  Answer dekho
  Answer (B) Nahi, unbalanced
  Stool chalne lagta hai, yaani uski velocity badalti hai: us par net force lag raha hoga.
2. Kaun zyada zor se push karta hai?
  RaviUska dost
  Answer dekho
  Answer (B) Uska dost
  Dost stool ko Ravi ki taraf push karta hai, aur stool usi taraf chalta hai. Isliye dost ka push Ravi ke push (aur friction milakar) se bada hai.

Quick check

3 mein se 1

Ek cart par east ki taraf

25 N

aur west ki taraf

40 N

ke forces lagte hain. Net force ka size kya hai?

Answer dekho

Answer 15 N

Forces ulte hain, isliye ghatao:

40 - 25 = 15 N

, west ki taraf, yaani bade force ki taraf. Inhe jodna (

65 N

) tabhi sahi hota jab dono ek hi taraf point karte.

6.3 Friction ka Force: Aksar Nazarandaaz, Par Hamesha Maujood

Chawal ki bhari bori ko halka sa push do to woh hilti kyun nahi? Jahan bori floor par tiki hai, wahan dono surfaces ke chhote-chhote ubhaar ek doosre mein atak jaate hain. Isse friction (घर्षण) paida hota hai, ek force jo hamesha sliding ke ulta point karta hai. Halka push karo to friction bhi utne hi zor se wapas push karta hai, isliye kuch nahi hota. Zyada zor se push karo to friction bhi badhta hai, lekin sirf ek limit tak. Us limit ke baad tumhara push jeet jaata hai, aage ki taraf net force lagta hai, aur bori sarakne lagti hai.

Definition

Friction

Woh force jo contact wali do surfaces ke saath-saath lagta hai aur unke ek doosre par slide karne ka virodh karta hai.

Floor par kheenche ja rahe crate par lagne wale saare forces banao, to tumhe do nahi, chaar forces milenge (Fig. 6.4). Do floor ke saath-saath lagte hain: rassi ka pull aur friction. Baaki do upar aur neeche lagte hain. Crate ka weight neeche point karta hai, aur floor jawab mein apni surface ke right angle par upar ki taraf push karta hai, yeh hai normal force (अभिलंब बल). Crate na floor mein dhansta hai na usse uchhalta hai, isliye yeh dono balanced hone chahiye. Air drag paanchva force hai, lekin dheere chalte crate par woh bahut chhota hai, isliye hum use chhod dete hain.

3/3Pull friction se bada hai, isliye aage ki taraf net force lagta hai.

Fig. 6.4Weight aur normal force balanced hain; pull aur friction tay karte hain ki crate ki speed badhegi ya nahi.NCERT Fig. 6.11 · p. 97

Floor par ek lakdi ka crate rakha hai aur uski right side par rassi bandhi hai. Step 1: crate se neeche ki taraf ek arrow par weight likha hai aur upar ki taraf barabar arrow par normal force; yeh vertical forces balanced hain. Step 2: rassi ke saath right ki taraf ek arrow par pull likha hai, aur floor ke saath left ki taraf ek dashed arrow par friction likha hai, jo pull se chhota hai. Step 3: right ki taraf ek green arrow par net force likha hai, kyunki pull friction se bada hai.

Definition

Normal force

Kisi surface ka us par rakhe object par push, jo surface ke perpendicular (right angle par) lagta hai.

Achhe strike ke baad carrom ki goti, haath se chhodi gayi toy car, ghaas par lurhakti football: har ek apne aap dheemi hokar ruk jaati hai. Yeh maan lena aasaan hai ki motion ko chalte rehne ke liye force chahiye. Asal mein, in sabko friction dheema kar raha hai. Earth par kisi cheez ko steady chalate rehne ke liye tumhe bas itna push karna hota hai ki friction cancel ho jaaye. Push hata do, to akela friction bachta hai jo object ko rok deta hai.

Activity 6.1NCERT Activity 6.1 · p. 98

Same launch, alag surfaces

Tumhe chahiye

ek rubber eraser
ek rubber band
do pencils aur thodi modelling clay (ya do bhari books)
ek ruler ya measuring tape
nishaan lagane ke liye chalk ya tape ki patti
chaar flat surfaces: floor par bichha newspaper, lakdi ki table, laminated table top, polished tile ya marble ka floor

Pehle guess karo

Tumhe kya lagta hai, eraser kis surface par sabse door tak slide karega?

Floor par newspaperLakdi ki tablePolished tilesChaaron par barabar

Do pencils ko modelling clay se lagbhag 8 cm door seedha khada karo (ya unhe do bhari books ke sahare khada karo) aur rubber band ko unke chaaron taraf aise lagao ki woh bas seedha rahe.
Band ke beech se 3 cm peechhe ek nishaan lagao. Yeh tumhara launch mark hai.
Eraser ko band ke beech mein tikao, ek ungli se use launch mark tak peechhe kheencho aur waise hi rok kar rakho. Phir apni ungli hata lo.
Naapo ki rukne se pehle eraser band se kitna door slide karta hai. Do baar launch karo aur dono distances note karo.
Set-up ko baaki har surface par le jao. Pencils ke beech ki doori same rakho aur har baar same mark tak peechhe kheencho.

Table 6.1

Surface	Try 1 (cm)	Try 2 (cm)
Newspaper
Lakdi
Laminate
Tiles

Tumhari entries apne aap save hoti hain.

Eraser pehle tez aur phir dheema kyun hota hai? Har stage par horizontal forces gino (Fig. 6.5). Mark par rokne par band use aage kheenchta hai aur tumhari ungli use peechhe push karti hai, aur yeh dono cancel ho jaate hain. Ungli hatao to sirf band aur friction bachte hain; band zyada strong hai, isliye net force aage point karta hai aur eraser ki speed badhti hai. Ek pal baad band seedha ho jaata hai aur eraser se uska touch chhoot jaata hai. Ab friction hi akela horizontal force hai. Woh peechhe point karta hai, isliye eraser ki speed zero tak gir jaati hai.

2/4Band ka push friction se bada: aage ki taraf net force, isliye eraser ki speed badhti hai.

Fig. 6.5Launch ke dauraan band friction ko hara deta hai; uske baad akela friction eraser ko dheema karke rok deta hai.NCERT Fig. 6.13 · p. 99

Upar se dikhti ek table jis par do pencils aur unke beech ek rubber band hai. Step 1: eraser peechhe kheencha gaya hai isliye band V shape banata hai; arrows dikhate hain ki band use aage kheenchta hai aur ek ungli use barabar force se peechhe rokti hai, isliye woh ruka rehta hai. Step 2: chhodne par band eraser ko lambe arrow se aage push karta hai jabki ek chhota dashed friction arrow peechhe point karta hai; eraser ki speed badhti hai. Step 3: eraser band se nikal chuka hai; sirf ek dashed friction arrow peechhe lagta hai aur uska velocity arrow chhota hai, isliye woh dheema hota hai. Step 4: eraser aage jaakar ruka hua hai, aur band se uski doori marked hai.

Activity 6.2NCERT Activity 6.2 · p. 99

Friction ka pull naapna

Tumhe chahiye

ek spring balance (0–10 N)
aadhi ret se bhari ek chhoti steel ki lunch box, jis par dhaaga bandha ho
Activity 6.1 wali chaaron surfaces

Pehle guess karo

Jis surface par eraser sabse door slide hua, us par balance ki reading hogi…

sabse zyadasabse kambaaki har surface jitni hi

Spring balance ko pehli surface par flat rakho aur check karo ki woh zero padhta hai. Lunch box ka dhaaga usse hook karo.
Balance ko surface ke saath kheencho, apna pull dheere-dheere badhao. Jis pal box bas sarakna shuru kare, us pal ki reading note karo.
Kheenchte raho taaki box dheemi, steady speed se slide karta rahe. Yeh reading bhi note karo.
Same box ke saath baaki teen surfaces par dohrao.

Table 6.2

Surface	Shuru (N)	Steady (N)
Newspaper
Lakdi
Laminate
Tiles

Tumhari entries apne aap save hoti hain.

Jab box steady speed se slide karta hai, to uski velocity nahi badalti, isliye us par net force zero hota hai. Tab balance ka pull aur friction barabar aur ulte hote hain, aur steady reading us surface ka friction naapti hai. Sabse kam reading us surface se aati hai jahan eraser sabse door slide hua tha, aur sabse zyada wahan se jahan woh sabse jaldi ruka tha. Tum yeh bhi dekh sakte ho ki box ko chalu karne mein use chalate rehne se thoda zyada pull lagta hai.

History seNCERT Scientist se Milo · p. 100

Galileo ki lurhakti balls

Lagbhag do hazaar saal tak log Greek vichaarak Aristotle se sehmat the ki chalti cheez ko chalte rehne ke liye lagaatar push chahiye aur push rukte hi woh ruk jaati hai. Roz ki zindagi isi baat ko sahi saabit karti lagti thi. 1600s ki shuruaat mein Italian scientist Galileo Galilei ne ramps par lurhakti balls ke experiments aur dhyaan se kiye gaye reasoning se is idea par sawaal uthaya.

Unka tark tha ki bina friction ke, ek ramp se neeche lurhakti ball doosre ramp par utni hi height tak chadhegi jahan se woh chali thi (Fig. 6.6). Doosre ramp ko kam dhalaan wala banao to ball ko us height tak pahunchne ke liye aur door lurhakna padega. Use flat kar do, to ball kabhi us height tak nahi pahunchegi, isliye woh hamesha lurhakti rahegi. Motion ko khud koi push nahi chahiye; sirf motion mein badlaav ko chahiye.

3/3Woh kabhi us height tak nahi pahunch sakti, isliye hamesha lurhakti rehti hai.

Fig. 6.6Agar friction na ho, to flat track par ball kabhi nahi rukegi.

Left mein ek ramp par oonchaai se ball chalti hai; ek dashed line poori picture mein uski shuruaati height dikhati hai, aur ek note kehta hai ki maan lo friction nahi hai. Step 1: doosra ramp steep hai, aur ball us par usi height par rukti hai jahan se chali thi. Step 2: doosra ramp kam dhalaan wala hai; ball us par aur door tak lurhakti hai lekin phir bhi usi height par rukti hai. Step 3: doosri surface flat hai; ball kabhi shuruaati height tak nahi pahunch sakti, isliye woh lurhakti rehti hai, jo ek lamba arrow dikhata hai.

History seNCERT Scientist se Milo · p. 100

Newton aur inertia

1687 mein English scientist Isaac Newton ne apni mahaan book, Principia, publish ki. Usmein unhone motion ke teen laws diye jinhe engineers aaj bhi bridges, cars aur space missions design karne mein use karte hain. Pehla law ek aisi property par tika hai jo har object mein hoti hai: woh chalaaye jaane, roke jaane ya ghumaaye jaane ka virodh karta hai. Newton ne is property ko inertia (जड़त्व) kaha. Bhare hue truck mein bicycle se kahin zyada inertia hota hai, isiliye use chalana ya rokna itna zyada mushkil hai.

Force ki unit unke naam par hai. Kisi insaan ke naam wali units ka ek seedha rule hai: poora naam chhote pehle letter se likha jaata hai, aur symbol capital se. Isliye hum newton aur N likhte hain, Newton aur n kabhi nahi.

6.4 Newton’s First Law of Motion

Galileo ka idea Newton ke teen laws mein se pehla ban gaya.

LawNewton's first law of motion

Jab tak kisi object par net force na lage, rest mein pada object rest mein hi rehta hai, aur chalta object usi speed se usi direction mein chalta rehta hai.

Law ko ulta padho to ek jaldi wala test mil jaata hai. Jab bhi kisi object ki velocity nahi badal rahi, chahe woh khada ho ya seedha aur steady chal raha ho, us par net force zero hai, aur uska acceleration bhi. Khada scooter khada hi rehta hai. Bilkul seedhe, level aur frictionless track par bina engine chalti train hamesha usi speed se usi direction mein chalti rahegi. Kyunki yeh inertia ko describe karta hai, isliye first law ko law of inertia bhi kehte hain.

Definition

Inertia

Object ki woh property jisse woh apni velocity mein kisi bhi badlaav ka virodh karta hai: jab tak net force na lage, woh rest mein rehta hai, ya seedhi line mein uniformly chalta rehta hai.

ExampleBus achanak brake lagaaye to passengers aage ki taraf jhatka khaate hain: unke sharir chalte rehna chahte hain.

Example 6.2NCERT Example 6.2 · p. 101

Lurhakta rehne wala thela

Ek sabzi wala apne chalte thele ko level road par push kar raha hai. Uska aage ka push thele par lagne wale friction ke bilkul barabar hai. Kya thela chalta rahega, ya dheere-dheere ruk jaayega?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 6.3NCERT Example 6.3 · p. 101

Net force zero hone par graphs

Seedhi road par do scooters mein se kisi par bhi net force nahi lagta. Scooter A road ke kinaare khada hai. Scooter B steady $10 m s^{- 1}$ se chal raha hai. Dono ke position–time aur velocity–time graphs sketch karo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

2/2Position steady badhti hai; velocity same rehti hai.

Fig. 6.7Zero net force: velocity constant, isliye velocity–time graph flat hai.NCERT Fig. 6.16 · p. 101

Do pairs of axes aamne-saamne: left mein position vs time, right mein velocity vs time. Step 1, khada scooter: position–time graph ek flat horizontal line hai aur velocity–time graph zero par time axis ke saath chalta hai. Step 2, steady velocity wala scooter: position–time graph upar ki taraf dhalaan wali seedhi line hai aur velocity–time graph time axis ke upar ek flat line hai.

Practice · 3 questions

Ruko aur socho 3–5: answers ke saath

Quick answerEasyNCERT Pause and Ponder Q3
Zameen ke paas ek baarish ki boond steady speed se seedhi neeche girti hai. Us par net force kya hai?
ZeroUska weight, neeche ki tarafHawa ka drag, upar ki tarafYeh zero nahi ho sakta, kyunki boond chal rahi hai
Answer dekho
Answer (A) Zero
Uski velocity constant hai, isliye uska acceleration aur net force zero hain. Uska weight neeche lagta hai, lekin hawa ka drag utne hi force se upar lagkar use cancel kar deta hai.
4
Quick answerMediumNCERT Pause and Ponder Q4
Hockey puck par koi net force nahi lagta. Inmein se kya ho sakta hai? Jitne sahi hain sab chuno.
Woh rest mein rehta haiWoh seedhi line mein constant speed se sarakta haiUski speed steady badhti haiWoh constant speed se circle mein ghoomta hai
Saare sahi options chuno
Answer dekho
Answer
(A) Woh rest mein rehta hai
(B) Woh seedhi line mein constant speed se sarakta hai
Zero net force par velocity nahi badal sakti, isliye puck ya to rest mein rehta hai ya constant velocity rakhta hai. Speed badhne se speed badalti hai, aur circle mein ghoomne se direction badalti hai, isliye dono ko net force chahiye.
Short answerMediumNCERT Pause and Ponder Q5
Hamare aas-paas lagbhag har cheez par forces lagte hain, phir bhi kisi object par net force zero ho sakta hai. Ek example do, aur cancel hone wale forces ke naam batao.
Solution dikhao
Chhat se sthir latka lamp: uska weight neeche lagta hai, aur uske wire ka pull utne hi force se upar lagta hai.
Ek aur example: seedhi, level road par steady speed se chalti car. Road ka uske driving wheels par aage ka push hawa ke peechhe ke drag aur motion ka virodh karne wale friction ko balance karta hai.

6.5 Newton’s Second Law of Motion

Chalna shuru karna, rukna, tez hona, dheema hona aur mudna, yeh sab velocity mein badlaav hain, aur velocity ka har badlaav ek acceleration hai. Isliye forces acceleration paida karte hain. Lekin net force aur acceleration aapas mein theek-theek kaise jude hain?

Activity 6.3NCERT Activity 6.3 · p. 102

Pull ko double karna

Tumhe chahiye

khule ghoomne wale wheels wala ek toy truck (ya chaar bottle-cap wheels par ek shoebox)
ek lamba dhaaga
ek smooth gol pencil jo table ke kinaare tape se chipki ho, pulley ka kaam karne ke liye
ek chhota kapde ka thaila aur kuch kanche (marbles)
ek kitchen scale
slow-motion video record karne wala phone

Pehle guess karo

Agar tum latke thaile ka mass double kar do, to truck utni hi doori tay karega…

utne hi time meinkam time meinzyada time mein

Yeh apne teacher ke saath class demonstration ke roop mein sabse achha kaam karta hai.

Lambi table ke ek sire ke paas start line banao aur doosre sire par pencil ko mazbooti se tape karo.
Dhaage ko truck ke aage baandho, use pencil ke upar se le jao aur uske sire par thaila latkao (Fig. 6.8). Thaile mein itne kanche daalo ki truck lurhakne lage, phir kanchon samet thaile ko tolo.
Truck ko start line par pakdo, recording shuru karo aur chhod do. Jab truck pencil tak pahunche to recording rok do.
Video ko dheere chalao aur note karo ki truck ne doori tay karne mein kitna time $T_{1}$ liya.
Thaile ka mass double karo, scale par check karo, aur $T_{2}$ nikaalne ke liye dohrao.

2/2Har run mein truck same doori kitne time mein tay karta hai, yeh naapo.

Fig. 6.8Girta load truck ko ek steady force se kheenchta hai.NCERT Fig. 6.17 · p. 102

Table ka side view. Left sire par start line par ek toy truck hai. Uske aage se ek dhaaga right kinaare par tape ki gayi gol pencil ke upar se hokar table top ke neeche latke kanchon ke chhote thaile tak jaata hai. Step 1: truck ko start line se chhoda jaata hai. Step 2: truck right ki taraf lurhak chuka hai aur thaila utna hi neeche aa gaya hai; table top ke neeche ek arrow tay ki gayi doori dikhata hai, jo har run mein same hai.

Table 6.3

Run	Thaila (g)	Time (s)
Load
Double

Tumhari entries apne aap save hoti hain.

DerivationDo times se do accelerations tak

Dono runs mein truck rest se shuru hota hai ( $u = 0$ ) aur constant acceleration ke saath same doori $s$ tay karta hai. Isliye $s = u t + \frac{1}{2} a t^{2}$ dono runs ke liye deta hai:

\begin{aligned} s & = \frac{1}{2} a_{1} T_{1}^{2} \\ s & = \frac{1}{2} a_{2} T_{2}^{2} \end{aligned}

Right-hand sides barabar hain, isliye:

\begin{aligned} a_{1} T_{1}^{2} & = a_{2} T_{2}^{2} \\ \frac{a_{2}}{a_{1}} & = \frac{T_{1}^{2}}{T_{2}^{2}} \end{aligned}

Jaise, $T_{1} = 2.0 s$ aur $T_{2} = 1.5 s$ ho to ratio $4.0 / 2.25 \approx 1.8$ hai. Pull double karne se acceleration lagbhag double ho gaya.

Activity 6.4NCERT Activity 6.4 · p. 103

Truck par load double karna

Pehle guess karo

Latka thaila wahi rakho, lekin truck par itna load rakho ki uska mass double ho jaaye. Ab truck lega…

kam timeutna hi timezyada time

Yeh Activity 6.3 ka follow-up hai, phir se class demonstration ke roop mein. Yeh ek doosri hypothesis test karta hai: same force ke saath bade mass ko chhota acceleration milta hai.

Activity 6.3 ke pehle run wala hi kanchon ka thaila use karo.
Truck ko tolo, phir uske andar cheezein (modelling clay ya chhota battery pack) tape karo jab tak uska mass double na ho jaaye.
Pehle ki tarah use start line se chhodo aur slow-motion video se time nikaalo.
Dono accelerations compare karne ke liye upar ki derivation wala ratio use karo.

Dono activities ek hi rule ki taraf ishaara karti hain: Newton ke laws mein se doosra, aur poori physics ke sabse kaam ke ideas mein se ek.

LawNewton's second law of motion

Jis object par net force lagta hai, woh us net force ki direction mein accelerate karta hai. Uska acceleration net force ke directly proportional aur object ke mass ke inversely proportional hota hai.

a = \frac{F}{m}

(6.1)

jahan

$a$: object ka acceleration
$F$: us par net force
$m$: uska mass

Newton's second law

F = m a

(6.2)

Yahan $F$ hamesha net force hai, koi akela force nahi, aur acceleration usi taraf point karta hai jidhar net force. Mass kilograms mein aur acceleration $m s^{- 2}$ mein ho to force newtons mein aata hai. Eq. (6.2) mein $m = 1 k g$ aur $a = 1 m s^{- 2}$ rakho:

\begin{aligned} F & = 1 k g \times 1 m s^{- 2} \\ = 1 k g m s^{- 2} \\ = 1 N \end{aligned}

Definition

Newton (N)

Force ki SI unit. Ek newton woh net force hai jo 1 kg mass ko $1 m s^{- 2}$ ka acceleration deta hai.

Ek patthar chhodo to woh tez aur tez girta hai: Earth ka pull use acceleration deta hai. Is khaas acceleration ka apna naam hai, acceleration due to gravity, aur apna symbol, $g$ (unit $m s^{- 2}$ ). Eq. (6.2) mein $a = g$ rakho to tumhe kisi bhi mass $m$ par Earth ke pull ka size milta hai, jo uska weight hai:

weight

F = m g

(6.3)

Zameen ke paas kahin bhi naapo, $g$ lagbhag $9.8 m s^{- 2}$ hota hai; yeh jagah ke saath bas thoda sa badalta hai. Mote calculations mein $10 m s^{- 2}$ kaafi hai.

Second law yeh bhi samjhata hai ki naram landing mein kam chot kyun lagti hai. Kisi chalte object ko rokne ke liye uski velocity zero tak laani padti hai. Yeh bahut kam time mein karne ka matlab hai bada deceleration, aur isliye, $F = m a$ ke hisaab se, bada force. Rukne ka time badha do to deceleration, aur force, bahut chhote ho jaate hain (Fig. 6.9).

3/3Lagbhag 0.1 s mein rukne par use sirf lagbhag 2.4 N chahiye aur woh bach jaata hai.

Fig. 6.9Velocity mein same badlaav, alag stopping times: jitna jaldi rukna, utna bada force.NCERT Fig. 6.18 · p. 104

Do ande saath-saath 4 metre per second se girte hain, ek left mein patthar ke floor ke upar aur ek right mein takiye ke upar. Step 1: dono ande same speed se gir rahe hain. Step 2: left wala anda patthar ke floor se takraata hai, lagbhag 0.004 second mein rukta hai, lagbhag 60 newton ka average force mehsoos karta hai aur toot jaata hai. Step 3: right wala anda takiye mein dhansta hai, lagbhag 0.1 second mein rukta hai, sirf lagbhag 2.4 newton ka average force mehsoos karta hai aur saboot rehta hai.

Numbers check karo: har anda ( $0.06 k g$ ) $4 m s^{- 1}$ khota hai. $0.004 s$ mein deceleration $1000 m s^{- 2}$ hai, jiske liye lagbhag $0.06 \times 1000 = 60 N$ chahiye. $0.1 s$ mein yeh sirf $40 m s^{- 2}$ hai, lagbhag $2.4 N$ . (Yeh average forces hain, ande ka chhota sa weight ignore kiya gaya hai.)

Isiliye tez throw pakadte waqt tum apne haath peechhe kheench lete ho. Holi par paani ka gubbara akadi baahon se pakdo to woh phat jaata hai. Haathon ko uske saath peechhe jaane do, to wahi gubbara zyada time mein dheema hota hai, use chhota force chahiye, aur woh bach jaata hai. Fielder ke 'peechhe hatte' haath bhi isi tarah kaam karte hain aur ungliyon ko bhi bachate hain.

Kabhi-kabhi hum bada force chahte hain. Keel par padta hathode ka sir second ke bahut chhote hisse mein rukta hai, isliye woh keel ko bahut bade force se dabata hai aur use lakdi mein ghusa deta hai. Jitna jaldi rukna, utna bada force.

Example 6.4NCERT Example 6.4 · p. 105

Coolie ka bojh

Railway ka ek coolie $24 k g$ mass ka suitcase sir par balance karke sthir khada hai. Uska sir suitcase par kitna bada upar ka force lagata hai? $g = 9.8 m s^{- 2}$ lo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 6.5NCERT Example 6.5 · p. 105

Kya almirah hilegi?

Asha level floor par khadi $40 k g$ mass ki steel almirah ko push karti hai. Us par friction zyada se zyada $120 N$ ho sakta hai, aur almirah sarakne lage to bhi $120 N$ hi rehta hai. Agar woh steady (a) $120 N$ (b) $140 N$ se push kare, to $3 s$ mein almirah kitna sarkegi?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

InteractiveForce lab: crate ko push karo

Floor par ek crate jis par teen arrows hain: blue mein tumhara push, orange mein friction aur green mein net force, har ek par newtons mein uska size likha hai. Ek slider push ko 0 se 60 newton tak set karta hai; buttons se bina friction ka floor, smooth tiles ya khurdara floor, aur 5, 10 ya 20 kilogram ka mass chuna jaata hai. Play das second ki motion chalata hai, aur ek button run ke dauraan push on ya off karta hai. Cards friction, net force, acceleration, velocity, distance aur time dikhate hain, ek status line batati hai ki kaun sa law kaam kar raha hai, aur crate ke chalte-chalte velocity–time graph banta hai.

Fig. 6.10Push, surface aur mass set karo, phir Play dabao. Run ke beech push off karke dekho ki akela friction kya karta hai.

1/3Speed badh rahi hai: positive slope, isliye aage ki taraf net force.

Fig. 6.11Velocity–time graph ka slope acceleration deta hai; net force ke liye use mass se multiply karo.NCERT Fig. 6.21 · p. 106

Ek velocity–time graph jismein time 0 se 14 second aur velocity 0 se 8 metre per second tak hai. Line 0 aur 4 second ke beech 0 se 6 metre per second tak seedhi upar jaati hai, 10 second tak 6 metre per second par flat rehti hai, phir 13 second par seedhi zero tak girti hai. Step 1 badhte hisse ko highlight karta hai: acceleration 1.5 metre per second squared aur north ki taraf 900 newton ka force. Step 2 flat hisse ko highlight karta hai: acceleration zero aur net force zero. Step 3 girte hisse ko highlight karta hai: acceleration minus 2 metre per second squared aur south ki taraf 1200 newton ka force.

Example 6.6NCERT Example 6.6 · p. 106

Velocity–time graph se forces padhna

Passengers samet ek e-rickshaw ka total mass $600 k g$ hai. Yeh seedhi road par north ki taraf chalta hai, aur Fig. 6.11 iska velocity–time graph hai. Is par net force nikaalo (a) $0$ se $4 s$ (b) $4$ se $10 s$ (c) $10$ se $13 s$ ke dauraan.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Practice · 3 questions

Ruko aur socho 6–8: answers ke saath

Quick answerEasyNCERT Pause and Ponder Q6
$250 g$ mass ki ek toy train seedhe track par steady $0.8 m s^{- 1}$ se chalti hai. Us par net force kya hai?
N
Answer dekho
Answer 0 N
Constant velocity ka matlab $a = 0$ , isliye $F = m a = 0$ . Mass aur speed ki zaroorat nahi: koi acceleration nahi, to koi net force nahi.
Short answerEasyNCERT Pause and Ponder Q7
Tum ek khaali shopping trolley aur ek poori bhari trolley ko same acceleration dena chahte ho. Kise bada push chahiye, aur kyun?
Solution dikhao
Bhari trolley ko. $F = m a$ ke hisaab se same acceleration ke liye mass ke proportion mein force chahiye. Agar bhari trolley ka mass khaali trolley se teen guna hai, to use teen guna net force chahiye.
Short answerMediumNCERT Pause and Ponder Q8
Naya television ek carton mein aata hai jismein uske chaaron taraf thermocol ke mote blocks hote hain. Carton gir jaaye to thermocol TV ko kaise bachata hai?
Solution dikhao
Jab carton floor se takraata hai, to thermocol dab jaata hai, isliye TV lagbhag turant rukne ki jagah zyada time mein rest mein aata hai. Zyada stopping time ka matlab chhota deceleration aur, $F = m a$ ke hisaab se, TV par chhota force, isliye uske tootne ke chances kam hote hain.

Quick check

4 mein se 1

12 k g

ki trolley par

30 N

ka net force lagta hai. Uska acceleration kya hai?

m s⁻²

Answer dekho

Answer 2.5 m s⁻²

a = F / m = 30 / 12 = 2.5 m s^{- 2}

. Iski jagah multiply karna (

30 \times 12

) formula ko gadbad kar deta hai.

6.6 Newton’s Third Law of Motion

Ab tak humne ek baar mein ek hi object ko follow kiya. Lekin force hamesha do objects ke beech interaction se aata hai. Table par thappad maaro to tumhari hatheli chubhti hai: jab tumhara haath table ko push karta hai, table bhi tumhare haath ko wapas push karti hai. Aise interaction mein dono objects ke saath kya hota hai?

Activity 6.5NCERT Activity 6.5 · p. 107

Dost ko push karo, khud chalo

Tumhe chahiye

smooth floor par wheels wali do chairs
ek dost
lagbhag 2 m lambi rassi ya dupatta

Pehle guess karo

Tum wheels wali ek chair par baith kar apne dost ki hatheliyon ko push karte ho; tumhara dost bas apni baahein akdi rakhta hai. Kya hota hai?

Sirf tumhara dost door lurhakta haiSirf tum peechhe lurhakte hoTum dono alag-alag lurhak jaate ho

Dono chairs ko lagbhag aadha metre door aamne-saamne rakho. Un par pair floor se upar utha kar baitho.
Apni hatheliyan dost ki hatheliyon par rakho. Dost apni baahein akdi rakhe aur tum ek zor ka push do. Dono chairs dekho.
Ab tum dono rassi ka ek-ek sira pakdo. Dost bas pakde rahe aur tum rassi ko apni taraf kheencho. Dono chairs phir se dekho.

Skateboarder ek pair se road ko peechhe ki taraf kick karta hai aur tezi se aage nikal jaata hai. Tumhara apna chalna bhi yahi trick hai, bas zyada halke se (Fig. 6.12). Har kadam par tumhara talwa zameen ko peechhe dabata hai. Zameen tumhare talwe ko utne hi force se aage dabati hai, aur yahi aage ka force tumhe aage le jaata hai. Dhyaan do yeh kis tarah ka force hai: friction. Hum aam taur par friction ko cheezein rokne wala force maante hain; chalne mein, yahi force tumhe aage badhata hai.

2/3Zameen friction ke zariye tumhare pair ko aage push karti hai.

Fig. 6.12Chalna ek third-law pair hai jo friction ki wajah se mumkin hota hai.NCERT Fig. 6.25 · p. 107

Zameen par ek taang aur joote ka side view. Step 1: zameen ke saath ek arrow peechhe point karta hai, jis par foot on ground likha hai: pair zameen ko peechhe push karta hai. Step 2: talwe par ek doosra arrow aage point karta hai, jis par ground on foot likha hai: zameen friction se pair ko aage push karti hai, yahi force chalne wale ko aage le jaata hai. Step 3: floor par tel faila hai; friction lagbhag nahi hai, aage ka push gayab ho jaata hai aur pair peechhe fisal jaata hai, ek dashed outline se door jo dikhata hai ki pair pehle kahan tha.

Activity 6.6NCERT Activity 6.6 · p. 108

Do balances, ek reading

Tumhe chahiye

do ek jaise spring balances
ek dost
ek mazboot darwaze ka handle ya hook

Pehle guess karo

Tum do spring balances ko aapas mein hook karte ho, aur tum aur tumhara dost unhe ulti taraf kheenchte ho. Balance A

6 N

padhta hai. Balance B kya padhta hai?

6 N

se kamBilkul

6 N

12 N

Yeh is par depend karta hai ki kaun zyada zor se kheenchta hai

Dono balances ko aapas mein hook karo aur table par flat rakho.
Ek khula sira tum pakdo aur doosra tumhara dost. Ulti directions mein halke se kheencho taaki balances sthir rahein, aur dono scales padho.
Zyada zor se kheencho, phir aur zyada, har baar dono scales padho.
Ab ek balance ko darwaze ke handle se baandho aur sirf doosre ko kheencho. Dono scales phir se padho.

Table 6.4

Pull	A (N)	B (N)
Halka
Zyada
Sabse zyada
Darwaze ka handle

Tumhari entries apne aap save hoti hain.

Abhi nahi kar sakte? Simulation try karo · Fig. 6.14

Aise experiments, anginat tareekon se dohraaye gaye, Newton's third law tak le jaate hain.

LawNewton's third law of motion

Agar object A object B ko push ya pull karta hai, to usi pal B bhi A ko aise force se push ya pull karta hai jo size mein barabar aur direction mein ulta hota hai.

Gym mein rassi par chadhne mein bhi yahi pairing hai: tumhare haath aur pair rassi ko neeche dabate hain, aur rassi tumhe upar dabati hai. Aur ab shikara ki paheli ka jawab mil gaya. Naav wale ka chappu paani ko stern (peechhe) ki taraf dhakelta hai; paani chappu ko bow (aage) ki taraf wapas dhakelta hai, aur chappu ko naav mein baitha naav wala pakde hue hai. Ek force paani par lagta hai, doosra chappu par, isliye cancel hone ko kuch nahi hai. Zyada zor se chappu chalao, to chappu par paani ka push badhta hai, isliye naav jaldi speed pakadti hai. Chaar tourists bitha do, to wahi push kahin bade mass ko accelerate karta hai, isliye speed dheere badhti hai (Section 6.5).

Activity 6.7NCERT Activity 6.7 · p. 109

Balloon se chalne wali car

Tumhe chahiye

ek lamba balloon
ek halki toy car (ya bottle-cap wheels par card ka base)
chipakne wali tape
ek drinking straw

Pehle guess karo

Hawa balloon se car ke peechhe ki taraf tezi se nikalti hai. Car kis taraf chalegi?

AagePeechheYeh nahi chalegi

Straw ko balloon ki gardan mein ghusao aur tape se seal karo taaki hawa leak na ho.
Balloon ko car ke upar tape karo, straw peechhe ki taraf bahar nikla rahe.
Straw se balloon phulao, straw ko dabakar band karo, aur car ko smooth floor par rakho.
Straw chhodo aur dekho.

Rocket bhi yahi idea use karta hai (Fig. 6.13). Uske engines fuel jalaate hain aur garam gas ki bahut badi maatra ko nozzles se neeche bahar dhakelte hain. Gas rocket ko utne hi force se upar push karti hai. Jab yeh upar ka push rocket ke weight se bada hota hai, to net force upar point karta hai aur rocket launch pad se uth jaata hai, jaise Sriharikota ke launches mein tumne shayad dekha ho.

2/3Gas rocket ko utne hi force se upar push karti hai; weight neeche lagta hai.

Fig. 6.13Engine gas ko neeche push karta hai; gas rocket ko upar push karti hai.NCERT Fig. 6.30 · p. 109

Ek rocket zameen par seedha khada hai aur uske nozzle ke neeche flame hai. Step 1: nozzle se neeche do arrows point karte hain, jin par engine pushes gas down likha hai. Step 2: rocket ke paas ek lamba green arrow upar point karta hai, jis par gas pushes rocket up likha hai, aur usse ek chhota arrow neeche point karta hai, jis par weight likha hai. Step 3: rocket zameen se upar uth gaya hai; ek note kehta hai ki upar ka push weight se bada hai.

Compare

Third-law pair ya balanced forces?

Third-law pair

Do alag objects par lagte hain
Hamesha size mein barabar aur direction mein ulte
Kabhi ek doosre ko cancel nahi karte
Example: pair zameen ko peechhe push karta hai, zameen pair ko aage push karti hai

Balanced forces

Same object par lagte hain
Barabar aur ulte sirf tab jab woh balance ho jaayein
Cancel ho jaate hain: net force zero hai
Example: book ka weight aur book par table ka push

Practice · 2 questions

Ruko aur socho 9–10: answers ke saath

Short answerMediumNCERT Pause and Ponder Q9
Ghoomne wale lawn sprinkler ki mudi hui baahein hoti hain jo paani ko side mein phenkti hain. Baahein gol-gol kyun ghoomti hain?
Solution dikhao
Har nozzle paani ko ek direction mein bahar push karta hai. Third law ke hisaab se paani nozzle ko utne hi force se ulti taraf push karta hai. Nozzles baahon ke siron par side ki taraf point karte hain, isliye yeh peechhe ke push baahon ko gol-gol ghumate hain.
Short answerHardNCERT Pause and Ponder Q10
Space station ke bahar tairti ek astronaut ki pakad chhoot gayi hai, aur koi safety line judi nahi hai. Uske haath mein ek bhari spanner hai. Woh station tak wapas kaise pahunch sakti hai?
Solution dikhao
Use spanner ko station se door wali direction mein zor se phenkna chahiye. Jab woh spanner ko push karti hai, spanner use barabar aur ulte force se push karta hai, isliye woh station ki taraf chalne lagti hai. Use dheema karne wala kuch nahi hai, isliye woh constant velocity se station ki taraf bahti rehti hai (first law). Spacecraft bhi isi tarah apne engines se gas bahar dhakel kar apni velocity badalta hai.

Kya dono objects ka chhoona zaroori hai? Nahi: third law non-contact forces par bhi laagu hota hai. Do magnets ek doosre ko barabar kheenchte, ya push karte, hain. Sookhe baalon mein ragadkar charge ki gayi kanghi kaagaz ke tukde ko attract karti hai, aur kaagaz bhi kanghi ko utni hi taakat se attract karta hai. Ped se girte nariyal ko Earth neeche kheenchti hai, jabki nariyal Earth ko bilkul utne hi force se upar kheenchta hai. Fig. 6.14 mein magnets ke saath khud explore karo.

SimulationAlag-alag magnets ke beech barabar pulls

Do bar magnets saath-saath rakhe hain aur unke chaaron taraf field lines hain; right wala magnet left wale se kahin zyada strong hai. Dono magnets par bane arrows dikhate hain ki har ek ko doosre se kitna force mehsoos hota hai. Tum kisi bhi magnet ko paas ya door drag kar sakte ho, aur attraction aur repulsion ke beech switch karne ke liye kisi ko bhi ulta palat sakte ho; dono force arrows hamesha lambai mein barabar aur direction mein ulte rehte hain.

Fig. 6.14Kisi bhi magnet ko drag karo, ya button se ek ko flip karo. Arrows dikhate hain ki har magnet ko kitna force mehsoos hota hai.NCERT Fig. 6.31 · p. 110

Try karo

Right wala magnet kahin zyada strong hai. Dono force arrows compare karo: kya koi ek lamba hai?
Ek magnet ko flip karo taaki same poles aamne-saamne hon. Dono arrows ka kya hota hai?
Magnets ko aur paas drag karo. Badhte hue bhi kya arrows barabar rehte hain?

Example 6.7NCERT Example 6.7 · p. 110

Earth nariyal ki taraf daud kar kyun nahi aati

$1.5 k g$ mass ka ek nariyal ped se girta hai. Earth nariyal ko $14.7 N$ ke force se neeche kheenchti hai, aur nariyal Earth ko $14.7 N$ se upar kheenchta hai. Earth ka mass lagbhag $6.0 \times 10^{24} k g$ hai. Dono ka acceleration nikaalo, aur samjhao ki sirf nariyal hi chalta kyun dikhta hai.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 6.8NCERT Example 6.8 · p. 110

Do skaters ek doosre ko door push karte hain

Aman ( $60 k g$ ) aur Riya ( $40 k g$ ) smooth floor par roller skates pehne aamne-saamne khade hain. Woh ek doosre ki hatheliyon par push karte hain, aur dono mein se har ek par push $120 N$ hai. Us pal har ek ke acceleration ka size nikaalo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

6.7 Objects ke System par Lagne wale Forces

Airport par ek coolie do luggage trolleys ko chhoti rassi se jod kar aage wali ko kheenchta hai. Yeh jodi kitni jaldi speed pakdegi? Aage wali trolley ka mass $m_{1}$ aur peechhe wali ka $m_{2}$ maano, aur coolie ka horizontal pull $F$ . Floor itna smooth hai ki friction ignore kiya ja sakta hai (Fig. 6.15).

Rassi khinchi hui hai, aur khinchi rassi apne siron se bandhi har cheez ko kheenchti hai. Woh peechhe wali trolley ko aage aur aage wali trolley ko peechhe barabar forces se kheenchti hai. Is pull ko tension, $T$ , kehte hain; yeh dono khinchaav rassi ke zariye aage badhaya gaya ek third-law pair hain.

2/3Dono ke chaaron taraf boundary banao: dono tensions internal hain aur cancel ho jaate hain, isliye sirf $F$ jodi ko accelerate karta hai.

Fig. 6.15Ek boundary ke andar tension forces cancel ho jaate hain; sirf external forces system ko accelerate karte hain.NCERT Fig. 6.34 · p. 111

Floor par do trolleys rassi se judi khadi hain, trolley 1 right mein aur trolley 2 left mein; F likha ek blue arrow trolley 1 ko right ki taraf kheenchta hai. Step 1: T likhe do chhote arrows dikhate hain ki rassi trolley 1 ko peechhe aur trolley 2 ko aage kheenchti hai. Step 2: dono trolleys aur rassi ke chaaron taraf ek dashed boundary banti hai; tension arrows dhundhle ho jaate hain, kyunki system ke andar woh cancel ho jaate hain, aur acceleration F divided by total mass hai. Step 3: vertical external forces jode jaate hain, neeche lagta total weight aur upar lagta floor ka total normal force, aur woh balance ho jaate hain.

Ab ek kadam peechhe hato aur dono trolleys aur rassi ko ek hi object, ek system, ki tarah dekho. Poocho ki kaun se forces iske bahar se aate hain. Floor ke saath sirf coolie ka pull: yeh ek external force hai. Dono tension forces system ke hisson ke beech aapas mein lagte hain, isliye woh internal hain; barabar aur ulte hone ki wajah se system ke liye unka sum zero hai. Isliye $m_{1} + m_{2}$ total mass wali poori jodi sirf $F$ se accelerate hoti hai:

a = \frac{F}{m_{1} + m_{2}}

(6.4)

jahan

$a$: dono trolleys ka saath mein acceleration
$F$: external pull
$m_{1} + m_{2}$: system ka total mass

Har trolley ko alag se solve karne par bhi yahi jawab aata hai, bas steps zyada hote hain; neeche ka example yeh check karta hai. Upar aur neeche bhi external forces hain, lekin woh cancel ho jaate hain: neeche lagta total weight $(m_{1} + m_{2}) g$ upar lagte floor ke normal forces $N_{1} + N_{2}$ se balance hota hai.

Definition

Tension

Woh kheenchne wala force jo khinchi hui string, rassi ya chain apne siron se bandhe objects par lagati hai.

Definition

External force

Chune gaye system par woh force jo uske bahar ki kisi cheez se aata hai. System ke hisson ke beech ke forces internal forces hain, aur woh pairs mein cancel ho jaate hain.

Example

Do trolleys kheenchna

Trolley 1 ( $20 k g$ ) aur trolley 2 ( $30 k g$ ) smooth floor par aapas mein bandhi hain. Trolley 1 par $100 N$ ka pull lagta hai. Jodi ka acceleration nikaalo, phir har trolley ko alag se dekh kar use check karo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Frictionless table par

5 k g

ka block aur

3 k g

ka block aapas mein bandhe hain aur unhe

24 N

se kheencha jaata hai. Unka acceleration kya hai?

m s⁻²

Answer dekho

Answer 3 m s⁻²

a = F / (m_{1} + m_{2}) = 24 / 8 = 3 m s^{- 2}

. Sirf ek block ka mass lene se yeh baat chhoot jaati hai ki dono ko accelerate hona hai.

Chalo explore kareinNCERT Khoj Jaari Hai · p. 115

Karke dekhne wale projects

Friction detective. Spring balance aur lunch box se pata lagao: kya box ko zyada zor se neeche dabane par (andar weights daal kar) friction badhta hai? Kya sarakna shuru karne ke liye lagne wala pull sarakte rehne wale pull se bada hai? Kya lurhakna (gol pencils par box) sarakne se aasaan hai? Apne jawabon ka ek infographic banao, aur samjhao ki wheel itna important invention kyun tha.
Magnet carts. Do ek jaisi toy cars mein se har ek par ek bar magnet lagao, same poles aamne-saamne. Unhe metre scale ke beech mein saath pakdo, chhodo, aur naapo ki har ek kitna door lurhakti hai. Dono cars par barabar load rakh kar dohrao; phir sirf ek car par load rakho. Distance vs mass ka graph banao aur second aur third laws se apne results samjhao.
Rassi aur khamba. Ek rassi ko smooth khambe ya ped ki daal par ek baar lapeto, ek sire se paani ki balti latkao aur doosra sira pakdo. Doosra aur teesra lapet jodo. Tumhe chahiye force kaise badalta hai? Isi tarah ek akela naavik jetty ke khambe ki madad se badi naav ko dhaara ke khilaaf rok kar rakh sakta hai.
Newton ko padho. Newton ki Principia (1687) ke shuruaati pages ka English translation online dhoondo, aur teen laws ke unke shabdon ko is chapter ke statements se compare karo.

Recap

Summary aur key points

Force magnitude aur direction wala push ya pull hai, jo newtons mein naapa jaata hai, jaise spring balance se (Section 6.1).
Ek line ke forces milkar net force banate hain: same direction wale jodo, ulte wale ghatao (Section 6.2).
Balanced forces zero net force dete hain aur motion nahi badal sakte; unbalanced forces badal sakte hain (Section 6.2).
Friction wahan lagta hai jahan surfaces chhooti hain aur sliding ka virodh karta hai; zyada smooth surfaces ke beech yeh kamzor hota hai (Section 6.3).
Level floor par object ka weight floor ke normal force se balance hota hai (Section 6.3).
First law: net force na ho to object rest mein rehta hai ya constant velocity rakhta hai; badlaav ka yeh virodh inertia hai (Section 6.4).
Second law: $a = F / m$ , acceleration net force ki direction mein; $1 N = 1 k g m s^{- 2}$ (Section 6.5).
Weight $F = m g$ hai, jahan Earth ki surface ke paas har object ke liye $g = 9.8 m s^{- 2}$ ((6.3)).
Zyada stopping time ka matlab chhota force: peechhe hatte haath, airbags aur naram landings (Fig. 6.9).
Third law: forces barabar aur ulte pairs mein aate hain jo do alag objects par lagte hain, isliye pair kabhi cancel nahi hota (Section 6.6).
Chalna, naav chalana, rockets aur recoil mein third-law pairs kaam karte hain; alag-alag masses par barabar forces alag-alag accelerations dete hain (Example 6.8).
Jude hue objects ko ek system maana ja sakta hai: $a = F / (m_{1} + m_{2})$ , tension jaise internal forces ko ignore karke (Section 6.7).

Practice · 20 questions

Practice questions answers ke saath (NCERT “Exercises”)

NumericalEasyNCERT Exercises Q1
Ek mazdoor gehun ki bori ko godown ke floor par $90 N$ ke horizontal pull se steady speed se ghaseet raha hai. Bori par friction kitna hai?
N
Answer dekho
Answer 90 N
Constant velocity par net force zero hota hai, isliye friction pull ke barabar hai: $90 N$ , motion ke ulta.
2
Quick answerEasyNCERT Exercises Q2
Ek air-hockey puck lagbhag frictionless table par sarakta hai. Har statement poora karo.
1. Us par net force na ho to puck ki velocity…
  same rahegibadhegighategi
  Answer dekho
  Answer (A) same rahegi
  First law: zero net force, velocity mein koi badlaav nahi.
2. Uski motion ki direction mein net force ho to uski speed…
  same rahegibadhegighategi
  Answer dekho
  Answer (B) badhegi
  Acceleration motion ki taraf point karta hai, isliye puck ki speed badhti hai.
3. Uski motion ki direction ke ulta net force ho to uski speed…
  same rahegibadhegighategi
  Answer dekho
  Answer (C) ghategi
  Acceleration motion ke khilaaf point karta hai, isliye puck dheema hota hai.
Quick answerEasyNCERT Exercises Q3
Smooth track par trolley X steady $2 m s^{- 1}$ se lurhak rahi hai. Trolley Y par east ki taraf $8 N$ aur west ki taraf $5 N$ ke forces lagte hain. Kaun sa statement sahi hai?
Sirf X par net force haiSirf Y par net force haiDono par net force haiKisi par net force nahi hai
Answer dekho
Answer (B) Sirf Y par net force hai
X ki velocity constant hai, isliye uska net force zero hai. Y ke forces unbalanced hain: east ki taraf $8 - 5 = 3 N$ .
NumericalMediumNCERT Exercises Q4
Ek rath utsav mein 40 bhakt lakdi ke rath ki rassiyan kheenchte hain. Unmein se 36 aage kheenchte hain, lekin 4 bheed mein ghoom jaate hain aur peechhe kheenchte hain. Har insaan $150 N$ se horizontally kheenchta hai. Rath par rassiyon ka net force nikaalo. (Friction aur baaki forces ignore karo.)
Solution dikhao
Answer $4800 N$ aage ki taraf
$\begin{aligned} F_{fwd} & = 36 \times 150 = 5400 N \\ F_{back} & = 4 \times 150 = 600 N \end{aligned}$
$F_{net} = 5400 - 600 = 4800 N$
Net force aage ki direction mein $4800 N$ hai. (Shortcut: $32$ logon jitna pull, $32 \times 150$ .)
Quick answerEasyNCERT Exercises Q5
$m$ mass wali body par net force $F$ lagta hai. Body accelerate karti hai…
$F$ ke khilaaf, $F$ bada ho to zyada $F$ ki taraf, $F$ bada ho to zyada $F$ ki taraf, $m$ bada ho to zyada $F$ ki taraf, $F$ bada ho to kam
Answer dekho
Answer (B) $F$ ki taraf, $F$ bada ho to zyada
Second law: acceleration net force ki taraf point karta hai aur uske proportional hota hai ( $a = F / m$ ). Bada mass chhota acceleration deta hai, bada nahi.
Quick answerMediumNCERT Exercises Q6
Neeche har graph dikhata hai ki ek object ki position time ke saath kaise badalti hai; har object seedhi line mein chalta hai. Kis object par net force lag raha hai?
Fig. 6.16Chaar objects ke position–time graphs.NCERT Fig. 6.37 · p. 113
Two-by-two grid mein chaar chhote position–time graphs. A ek horizontal line hai. B origin ke paas se upar jaati seedhi line hai. C oonchaai se neeche girti seedhi line hai. D ek curve hai jo pehle tezi se upar jaata hai aur phir flat ho jaata hai.
ABCD
Answer dekho
Answer (D) D
A rest mein hai; B aur C seedhi lines hain, isliye woh constant velocity se chalte hain (C wapas start ki taraf). Teenon par zero net force. D ka slope badalta rehta hai (woh dheema ho raha hai), isliye uski velocity badalti hai aur us par net force lagta hai.
Short answerMediumNCERT Exercises Q7
Priya skateboard par khadi hai aur ek bhari school bag aage apni dost ki taraf phenkti hai. Priya aur skateboard ke saath kya hota hai? Samjhao.
Solution dikhao
AnswerWoh peechhe lurhak jaati hai.
Bag ko aage phenkne ke liye Priya use aage push karti hai. Third law ke hisaab se bag Priya ko barabar force se peechhe push karta hai. Skateboard ke wheels use aasaani se chalne dete hain, isliye woh aur skateboard bag ke ulta, peechhe lurhak jaate hain.
Short answerMediumNCERT Exercises Q8
Deewar se sakht zameen par koodte waqt land karte hue ghutne kyun modne chahiye?
Solution dikhao
Land karte waqt tumhari neeche ki velocity zero tak girni hi hai. Ghutne modne se yeh rukna zyada time mein failta hai. Zyada stopping time ka matlab chhota deceleration aur isliye, $F = m a$ ke hisaab se, tumhari taangon aur joints par chhota force. Seedhi taangon se land karne par tum lagbhag turant ruk jaate ho, kahin bade force ke saath.
Quick answerEasyNCERT Exercises Q9
Bhari ladi bailgaadi ek khaali cycle-rickshaw se takraati hai. Takkar ke dauraan…
gaadi rickshaw ko zyada zor se push karti hai jitna rickshaw gaadi kokoi kisi ko push nahi kartadono ek doosre ko same size ke force se push karte hainrickshaw gaadi ko zyada zor se push karta hai jitna gaadi rickshaw ko
Answer dekho
Answer (C) dono ek doosre ko same size ke force se push karte hain
Dono forces ek third-law pair banate hain, isliye woh size mein barabar aur direction mein ulte hain. Halke rickshaw ko bada acceleration milta hai, isiliye lagta hai ki use zyada zor se takkar lagi.
10
DiagramMediumNCERT Exercises Q10
Ek student frictionless track par alag-alag mass ke blocks par same force lagata hai aur accelerations table mein record karta hai.
Table 6.5
Mass (kg) Acceleration ( $m s^{- 2}$ )
0.5 12
1 6
2 3
4 1.5
1. Student ne kitna force lagaya?
  N
  Answer dekho
  Answer 6 N
  Har row ke liye $F = m a$ : $0.5 \times 12 = 1 \times 6 = 2 \times 3 = 4 \times 1.5 = 6 N$ .
2. In readings ke liye force–mass graph sketch karo.
  Solution dikhao
  Har row same force deti hai, $6 N$ . Isliye force–mass graph $F = 6 N$ par ek horizontal seedhi line hai, mass axis ke parallel, $0.5 k g$ se $4 k g$ tak. (Acceleration–mass graph ek curve hai, kyunki $m$ badhne par $a = 6 / m$ ghatta hai.)
NumericalMediumNCERT Exercises Q11
Seedhi line mein chalti $4 k g$ ki cart ka velocity–time graph diya gaya hai. Cart par net force nikaalo.
Fig. 6.17Cart ka velocity–time graph.NCERT Fig. 6.41 · p. 114
Ek velocity–time graph jismein time 0 se 7 second aur velocity 0 se 16 metre per second tak hai. Ek seedhi line time zero par 2 metre per second se shuru hoti hai aur 6 second par 14 metre per second tak jaati hai, jahan dashed guide lines axes se milti hain.
N
Solution dikhao
$a = \frac{14 - 2}{6 - 0} = 2 m s^{- 2}$
$F = m a = 4 \times 2 = 8 N$
Net force motion ki direction mein $8 N$ hai, aur yeh constant hai kyunki graph ek seedhi line hai.
NumericalHardNCERT Exercises Q12
$60 m s^{- 1}$ se udta $30 g$ mass ka teer ghaas ke gatthar se takraata hai aur usmein $20 c m$ jaakar ruk jaata hai. Constant deceleration maan kar teer par average stopping force nikaalo.
N
Solution dikhao
Yahan $u = 60 m s^{- 1}$ , $v = 0$ , $s = 0.20 m$ aur $m = 0.030 k g$ .
$\begin{aligned} 0 & = 60^{2} + 2 a (0.20) \\ a & = - \frac{3600}{0.40} = - 9000 m s^{- 2} \end{aligned}$
$\begin{aligned} F & = m a = 0.030 \times 9000 \\ = 270 N \end{aligned}$
Ghaas teer ko lagbhag $270 N$ se uski motion ke ulta wapas push karti hai.
NumericalHardNCERT Exercises Q13
Ek hockey player rest mein padi $0.16 k g$ mass ki ball ko maarta hai. Ball stick se $90 k m h^{- 1}$ par nikalti hai. Agar ball par stick ka average force $400 N$ hai, to stick aur ball kitni der contact mein rahe?
s
Solution dikhao
$v = 90 \times \frac{1000}{3600} = 25 m s^{- 1}$
$a = \frac{F}{m} = \frac{400}{0.16} = 2500 m s^{- 2}$
$t = \frac{v - u}{a} = \frac{25 - 0}{2500} = 0.01 s$
Contact sirf lagbhag $0.01 s$ , yaani second ka sauvaan hissa, rehta hai.
NumericalHardNCERT Exercises Q14
$6 m s^{- 1}$ se sarakta $5 k g$ ka box ek khurdari mat par aata hai, jahan us par friction $12 N$ hai. Usi pal ek bachcha uski motion ke khilaaf steady $8 N$ se push karta hai. Rukne se pehle box mat par kitni door jaata hai?
m
Solution dikhao
Dono forces motion ke khilaaf lagte hain, isliye net force peechhe point karta hai:
$F = 12 + 8 = 20 N$
$a = - \frac{20}{5} = - 4 m s^{- 2}$
$\begin{aligned} 0 & = 6^{2} + 2 (- 4) s \\ s & = \frac{36}{8} = 4.5 m \end{aligned}$
Rukne se pehle box mat par $4.5 m$ sarakta hai.
15
Long answerHardNCERT Exercises Q15
Nadi ke kinaare ek winch steady force $F$ se kheenchti hai. Akele raft ko kheenchne par woh raft ko acceleration $a_{1}$ deti hai. Akeli chhoti naav ko kheenchne par woh naav ko acceleration $a_{2}$ deti hai. Ab raft ko naav ke peechhe baandh diya jaata hai aur wahi force $F$ dono ko saath kheenchta hai. Paani ka drag ignore karo.
1. Naya acceleration $a_{1}$ aur $a_{2}$ ke roop mein nikaalo.
  Solution dikhao
  Answer $a = \frac{a_{1} a_{2}}{a_{1} + a_{2}}$
  $F = m a$ se masses hain $m_{1} = F / a_{1}$ (raft) aur $m_{2} = F / a_{2}$ (naav). Judi hui jodi ke liye Eq. (6.4) deta hai:
  $\begin{aligned} a & = \frac{F}{m_{1} + m_{2}} \\ = \frac{F}{F / a_{1} + F / a_{2}} \end{aligned}$
  $a = \frac{1}{1 / a_{1} + 1 / a_{2}} = \frac{a_{1} a_{2}}{a_{1} + a_{2}}$
2. Agar $a_{1} = 3 m s^{- 2}$ aur $a_{2} = 6 m s^{- 2}$ hai, to naya acceleration nikaalo.
  m s⁻²
  Answer dekho
  Answer 2 m s⁻²
  $a = (3 \times 6) / (3 + 6) = 18 / 9 = 2 m s^{- 2}$ , akele kisi bhi ek se chhota, jaisa bade total mass ke liye hona chahiye.
Short answerMediumNCERT Exercises Q16
Table par padi steel ki paper clip se kuch centimetre upar ek strong magnet pakdo. Clip uchhal kar magnet tak aa jaati hai, lekin tumhe magnet ka hilna mushkil se mehsoos hota hai. Magnet aur clip ek doosre ko barabar forces se kheenchte hain, to phir sirf clip hi saaf taur par kyun hilti hai?
Solution dikhao
Third law ke hisaab se forces barabar aur ulte hain. Clip ka mass bahut chhota hai, isliye magnet ka pull use bada acceleration deta hai ( $a = F / m$ ), aur pull uska weight paar karne ke liye kaafi hai. Magnet kahin bhari hai, aur tumhara haath use pakde hue hai: tumhara haath ek balancing force deta hai, isliye magnet par net force lagbhag zero rehta hai aur woh mushkil se hilta hai.
Quick answerEasy
Constant velocity se chalte object par koi bhi force nahi lagna chahiye.
SahiGalat
Answer dekho
Answer Galat
Forces lag sakte hain, lekin unhe balance hona chahiye taaki net force zero ho, jaise steady chalte thele par push aur friction.
Quick answerEasy
Ek newton woh net force hai jo kg mass ko $1 m s^{- 2}$ ka acceleration deta hai.
Answer dekho
Answer 1
$1 N = 1 k g \times 1 m s^{- 2}$ .
19
Quick answerMedium
Inhe paida hone wale acceleration ke order mein lagao, sabse chhota pehle.
1. $20 k g$ par $10 N$
2. $8 k g$ par $40 N$
3. $4 k g$ par $6 N$
4. $4 k g$ par $12 N$
Answer dekho
Answer
$20 k g$ par $10 N$
$4 k g$ par $6 N$
$4 k g$ par $12 N$
$8 k g$ par $40 N$
$a = F / m$ se: $0.5$ , $1.5$ , $3$ aur $5 m s^{- 2}$ .
Quick answerMedium
$1200 k g$ mass ki ek car seedhi road par $5 s$ mein $10 m s^{- 1}$ se $20 m s^{- 1}$ tak speed badhati hai. Us par net force kya hai?
N
Answer dekho
Answer 2400 N
$a = (20 - 10) / 5 = 2 m s^{- 2}$ , isliye $F = 1200 \times 2 = 2400 N$ .

Mass (kg)	Acceleration ( $m s^{- 2}$ )
0.5	12
1	6
2	3
4	1.5

Apna NCERT exercise question dhoondo

Hamare practice questions ncert.ai ke liye likhe gaye hain aur NCERT exercises ko follow karte hain. Apni textbook ke question se match karne wala question dhoondo; uska answer uske saath hai.

Tumhari NCERT textbook mein	Yahan practice question
NCERT Pause and Ponder Q1	Ruko aur socho 1–2 · Q1
NCERT Pause and Ponder Q2	Ruko aur socho 1–2 · Q2
NCERT Pause and Ponder Q3	Ruko aur socho 3–5 · Q3
NCERT Pause and Ponder Q4	Ruko aur socho 3–5 · Q4
NCERT Pause and Ponder Q5	Ruko aur socho 3–5 · Q5
NCERT Pause and Ponder Q6	Ruko aur socho 6–8 · Q6
NCERT Pause and Ponder Q7	Ruko aur socho 6–8 · Q7
NCERT Pause and Ponder Q8	Ruko aur socho 6–8 · Q8
NCERT Pause and Ponder Q9	Ruko aur socho 9–10 · Q9
NCERT Pause and Ponder Q10	Ruko aur socho 9–10 · Q10
NCERT Exercises Q1	Exercises · Q1
NCERT Exercises Q2	Exercises · Q2
NCERT Exercises Q3	Exercises · Q3
NCERT Exercises Q4	Exercises · Q4
NCERT Exercises Q5	Exercises · Q5
NCERT Exercises Q6	Exercises · Q6
NCERT Exercises Q7	Exercises · Q7
NCERT Exercises Q8	Exercises · Q8
NCERT Exercises Q9	Exercises · Q9
NCERT Exercises Q10	Exercises · Q10
NCERT Exercises Q11	Exercises · Q11
NCERT Exercises Q12	Exercises · Q12
NCERT Exercises Q13	Exercises · Q13
NCERT Exercises Q14	Exercises · Q14
NCERT Exercises Q15	Exercises · Q15
NCERT Exercises Q16	Exercises · Q16

Quick check: MCQs

6.1.1 Force ki magnitude naapna3 questions
6.2 Balanced aur Unbalanced Forces3 questions
6.3 Friction ka Force: Aksar Nazarandaaz, Par Hamesha Maujood3 questions
6.4 Newton’s First Law of Motion3 questions
6.5 Newton’s Second Law of Motion4 questions
6.6 Newton’s Third Law of Motion4 questions
6.7 Objects ke System par Lagne wale Forces3 questions

Glossary · 12

Key terms (English + Hindi)

action–reaction pairक्रिया-प्रतिक्रिया युग्मkriya-pratikriya yugm: Woh do barabar aur ulte forces jo interact karne wale do objects ek doosre par lagate hain. Yeh alag-alag objects par lagte hain.Chapter mein pehli baar yahan aaya →

balanced forcesसंतुलित बलsantulit bal: Object par woh forces jinka net force zero ho, isliye milkar woh uski motion nahi badal sakte. Net force zero na ho to forces unbalanced hain.Chapter mein pehli baar yahan aaya →

external forceबाह्य बलbaahya bal: Chune gaye system par uske bahar ki kisi cheez se aane wala force. System ke hisson ke beech ke forces internal hain aur pairs mein cancel ho jaate hain.Chapter mein pehli baar yahan aaya →

forceबलbal: Kisi object par lagne wala push ya pull jo kisi doosre object ke saath uske interaction se aata hai. Iski magnitude aur direction hoti hai.Chapter mein pehli baar yahan aaya →
frictionघर्षणgharshan: Contact wali do surfaces ke beech ka force jo unke ek doosre par slide karne ka virodh karta hai.Chapter mein pehli baar yahan aaya →

inertiaजड़त्वjadatva: Object ki woh property jisse woh apni velocity mein kisi bhi badlaav ka virodh karta hai, chahe woh rest mein ho ya chal raha ho.Chapter mein pehli baar yahan aaya →

momentumसंवेगsanveg: Mass guna velocity, $p = m v$ . Yeh velocity ki direction mein point karta hai.Chapter mein pehli baar yahan aaya →

net forceपरिणामी बलparinaami bal: Woh akela force jiska effect object par lagne wale saare forces ke milkar lagne jaisa hi ho.Chapter mein pehli baar yahan aaya →
newtonन्यूटनnyootan: Force ki SI unit (symbol N): woh net force jo 1 kg mass ko $1 m s^{- 2}$ ka acceleration deta hai.Chapter mein pehli baar yahan aaya →
normal forceअभिलंब बलabhilamb bal: Kisi surface ka us par rakhe object par push, jo surface ke right angle par lagta hai.Chapter mein pehli baar yahan aaya →

tensionतनावtanaav: Woh kheenchne wala force jo khinchi hui string, rassi ya chain apne siron se bandhe objects par lagati hai.Chapter mein pehli baar yahan aaya →

weightभारbhaar: Gravity ka woh pull jo Earth kisi object par lagati hai, $m g$ ke barabar.Chapter mein pehli baar yahan aaya →

6.1 Force ka Concept

6.1.1 Force ki magnitude naapna

6.2 Balanced aur Unbalanced Forces

6.3 Friction ka Force: Aksar Nazarandaaz, Par Hamesha Maujood

6.4 Newton’s First Law of Motion

6.5 Newton’s Second Law of Motion

6.6 Newton’s Third Law of Motion

6.7 Objects ke System par Lagne wale Forces

Apna NCERT exercise question dhoondo

Quick check: MCQs

Tum chapter ke end tak pahunch gaye