Measurement of Length and Motion

Pehle ke time mein, log length measure karne ke liye apni body parts use karte the. Jaise:

• Handspan (Balisht): Angoothe aur chhoti ungli ke beech ki doori. Har insaan ka handspan alag hota hai, isliye measurement mein variation aata tha.
• Example: Table ki length measure karna.
• Foot (Pair): Pair ki length use karke distance measure karna.
• Cubit (Haath): Elbow se middle finger tip tak ki length.
• Pace/Stride (Kadam): Ek kadam ki length.

In methods ki problems:

• Non-standard: Har person ke body parts ka size alag hota hai. Isliye, ek hi cheez ko alag-alag log measure karte the toh alag-alag readings aati thi.
• Confusion: Jab log ek jagah se doosri jagah travel karte the aur measurements share karte the, toh bahut confusion hoti thi. Imagine, ek tailor ne 'do haath' kapda manga, par uske haath chote the, aur kapda dene wale ke haath bade! Toh kapda zyada mil jaata tha ya kam.

Is non-uniformity ki wajah se, ek standard system ki zaroorat mehsoos hui.

Confusion ko khatam karne ke liye, duniya ke sabhi countries ne milkar ek common system of units adopt kiya, jise International System of Units (SI Units) kehte hain.

SI Unit of Length:

• Length ki SI unit metre hai. Iska symbol m hai.
• Metre scale: Ek metre scale 100 equal parts mein divided hota hai.

Smaller Units:

• Centimetre (cm): 1 metre = 100 centimetres. Yaani, 1 cm = \(\frac{1}{100}\) m.
• Ek metre scale par har division 1 cm ka hota hai.
• Millimetre (mm): 1 centimetre = 10 millimetres. Yaani, 1 mm = \(\frac{1}{10}\) cm.
• 1 mm sabse chhoti length hai jo hum normal ruler se measure kar sakte hain.
• 1 mm = \(\frac{1}{1000}\) m.

Larger Units:

• Kilometre (km): Badi distances measure karne ke liye use hota hai, jaise do cities ke beech ki doori.
• 1 kilometre = 1000 metres.

Conversions (Important for numericals):

• 1 km = 1000 m
• 1 m = 100 cm
• 1 cm = 10 mm

Summary Table of Units:

| Unit | Symbol | Relation to Metre | Use Case | | :---------- | :----- | :---------------- | :----------------------------------------- | | Kilometre | km | 1000 m | Cities ke beech ki doori, road travel | | Metre | m | Base Unit | Room ki length, kapde ki length | | Centimetre | cm | 0.01 m | Pencil ki length, book ki width | | Millimetre | mm | 0.001 m | Smallest measurements, wire ki thickness |

Standard units use karne se measurements consistent aur reliable ho jaate hain, chahe koi bhi measure kare.

Length measure karte time accuracy bahut important hai. Kuch common mistakes hoti hain jinhe avoid karna chahiye:

1. Scale ko sahi tarike se rakhna:

• Correct: Scale ko object ke bilkul contact mein aur uski length ke along rakhna chahiye. Koi gap nahi hona chahiye.
• Incorrect: Scale ko object se door rakhna ya tedha rakhna galat hai. Isse reading galat aayegi.

2. Broken ya worn-out scale use karna:

• Agar scale ka end broken hai ya zero marking clear nahi hai, toh bhi use use kar sakte hain.
• Method: Measurement zero se start karne ke bajaye, kisi aur full mark se start karo, jaise 1.0 cm.
• Calculation: Final reading mein se starting mark ki reading ko subtract kar do.
• Example: Agar object 1.0 cm se 13.5 cm tak hai, toh length = 13.5 cm - 1.0 cm = 12.5 cm.

3. Eye position (Parallax Error):

• Reading lete time aankh ki position bilkul object ke tip ke upar honi chahiye, jahan measurement li ja rahi hai.
• Agar aankh side se dekhegi (left ya right), toh reading galat aayegi. Is error ko Parallax Error kehte hain.
• Correct: Eye position 'B' (directly above).
• Incorrect: Eye position 'A' (left) ya 'C' (right).

Summary of Correct Measurement Steps:

1. Contact: Scale ko object ke saath contact mein rakho, uski length ke along.
2. Starting Point: Agar zero mark clear nahi hai, toh kisi aur full mark (e.g., 1 cm) se start karo.
3. Eye Position: Aankh ko measurement point ke bilkul upar rakho (avoid parallax error).
4. Reading: Final mark se starting mark ko subtract karke actual length nikalo.

Straight lines ko measure karna toh easy hai, par curved lines ko kaise measure karein? Jaise, ek river ka path ya ek thread jo tedha rakha ho.

Method 1: Using a flexible measuring tape:

• Agar available ho, toh flexible measuring tape (jaise tailor use karte hain) directly curved line par rakh kar measure kar sakte hain.

Method 2: Using a thread (dhaaga):

Yeh ek common aur practical method hai:

1. Thread ko align karo: Ek thread ka ek end curved line ke starting point par rakho.
2. Slowly trace karo: Apne thumb aur finger ki help se, thread ko curved line ke along dheere-dheere move karte jao, uski shape ko follow karte hue.
3. Mark the end: Jab thread curved line ke end point tak pahunch jaaye, toh wahan thread par ek mark laga do (ya use cut kar do).
4. Straighten aur Measure: Ab is thread ko seedha karo aur ek metre scale ya ruler par rakh kar uski length measure karo.

Is tarah, curved line ki actual length mil jaati hai.

Kisi bhi object ki position batane ke liye, humein ek reference point ki zaroorat hoti hai.

• Reference Point: Ek fixed object ya point jiske respect mein hum kisi doosre object ki position ya distance batate hain.
• Example: "Mera ghar school se 2 km door hai." Yahan school ek reference point hai.
• Example: "Bus stand se 500m aage Deepa ka ghar hai." Yahan bus stand reference point hai.

Importance of Reference Point:

• Clearity: Reference point ke bina, kisi object ki position batana mushkil ya confusing ho sakta hai. Agar main bolun 'mera ghar 2 km door hai', toh kahan se 2 km door?!
• Relative Position: Sabhi positions relative hoti hain. Ek object ki position doosre object ke respect mein define ki jaati hai.
• Kilometre Stones: Roads par jo kilometre stones hote hain (jaise 'Delhi 70 km'), woh bhi ek reference point (Delhi) ke respect mein distance batate hain.

Motion ko samajhne ke liye reference point bahut zaroori hai.

Humare aas-paas bahut saari cheezein move karti hain aur bahut saari stationary (rukhi hui) hoti hain. Inhe define karne ke liye hum reference point ka use karte hain.

1. Motion:

• Ek object motion mein tab hota hai jab uski position time ke saath reference point ke respect mein change hoti hai.
• Example: Ek car road par chal rahi hai. Agar hum road side ke tree ko reference point maane, toh car ki position tree ke respect mein change ho rahi hai, so car is in motion.
• Example: Ek flying bird, ek moving train, ek swinging pendulum.

2. Rest:

• Ek object rest par tab hota hai jab uski position time ke saath reference point ke respect mein change nahi hoti.
• Example: Ek tree road side par khada hai. Agar hum us tree ko reference point maane, toh uski position khud ke respect mein change nahi ho rahi. So, tree is at rest.
• Example: Ek table, ek chair, ek building.

Relative Nature of Motion:

• Motion aur Rest dono relative terms hain. Ek hi object ek reference point ke liye motion mein ho sakta hai aur doosre reference point ke liye rest par.
• Example: Ek train mein baitha hua passenger.
• Train ke andar baithe doosre passenger ke liye: Woh passenger rest par hai (position change nahi ho rahi).
• Platform par khade insaan ke liye: Woh passenger motion mein hai (position change ho rahi hai).

Activity 5.2: Objects in Motion vs. At Rest

| Objects in Motion | Justification | Objects at Rest | Justification | | :--------------------- | :------------------------------------------------ | :-------------- | :---------------------------------------------- | | Flying bird | Position changes w.r.t. ground | Tree | Position does not change w.r.t. ground | | Moving car | Position changes w.r.t. road | House | Position does not change w.r.t. ground | | Clock hands | Position changes w.r.t. clock face | Table | Position does not change w.r.t. room | | Person walking | Position changes w.r.t. stationary objects | Book | Position does not change w.r.t. table | | Leaves falling from tree | Position changes w.r.t. tree/ground | Mountain | Position does not change w.r.t. surrounding land |

Motion ko hamesha ek reference point ke respect mein hi define kiya jaata hai.

Objects alag-alag tarah se move karte hain. Unke path ke according, motion ko categorize kiya ja sakta hai:

1. Linear Motion (Rectilinear Motion):

• Jab koi object seedhi line mein move karta hai.
• Examples: March past karte soldiers, car moving on a straight road, train on a straight track, falling stone, bullet fired from a gun.

2. Circular Motion:

• Jab koi object ek circular path mein move karta hai.
• Examples: Fan ke blades ki motion, merry-go-round ki motion, earth ki motion around the sun (approx circular), ek string se bandhe patthar ko ghumana.
• Isme object ki distance ek fixed point (centre) se hamesha same rehti hai.

3. Oscillatory Motion (To and Fro Motion):

• Jab koi object ek fixed position ke around 'to and fro' (aage-peeche) ya 'up and down' move karta hai.
• Examples: Pendulum ki motion, swing (jhoola) ki motion, sewing machine ki needle ki motion, guitar string ki vibration.
• Is motion mein object apne mean position ke around repeat karta hai.

4. Periodic Motion:

• Jab koi motion ek fixed interval of time ke baad repeat hoti hai.
• Examples: Clock ke hands ki motion, earth ki rotation (24 hours), earth ki revolution around sun (365 days), pendulum ki oscillatory motion.
• Har oscillatory motion periodic hoti hai, par har periodic motion oscillatory nahi hoti (e.g., circular motion bhi periodic ho sakti hai, jaise fan blades ki motion).

Multiple Types of Motion:

• Ek object mein ek se zyada tarah ki motion bhi ho sakti hai.
• Example: Ek cycle ka wheel:
• Circular motion: Wheel apne axle ke around rotate karta hai.
• Linear motion: Cycle aage badhti hai, toh wheel bhi seedhi line mein move karta hai.
• Example: Sewing machine:
• Circular motion: Flywheel ki motion.
• Oscillatory motion: Needle ki upar-neeche motion.

Activity 5.7: Children's Park mein Motion

| Object/Activity | Type of Motion | | :-------------- | :--------------------------------------------------- | | Slide | Linear motion (seedhi line mein neeche aana) | | Merry-go-round | Circular motion (fixed axis ke around ghumna) | | Swing (Jhoola) | Oscillatory motion (fixed point ke around to and fro) | | See-saw | Oscillatory motion (up and down around a central pivot) |

Motion ke types ko examples ke saath samajhna bahut zaroori hai.