Assertion (A): A car moving in city traffic often exhibits non-uniform motion. Reason (R): In city traffic, the car's speed and direction frequently change due to signals, other vehicles, and turns.

A and R both correct, R explains A

The diagram shows a simple pendulum. Which of the following statements about its motion are correct?

The bob has maximum speed at position O.

The bob stops momentarily at position O.

The bob has maximum potential energy at positions A and B.

The time taken to go from A to B is one time period.

Which of the following statements correctly describe uniform linear motion?

The object covers equal distances in equal intervals of time.

The speed of the object remains constant.

The object's path is always curved.

The object's acceleration is continuously changing.

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The main 'Game Mode' quiz contains 40 questions, covering easy, medium, and hard difficulty levels. There are also solved NCERT book questions and a monthly test.

Is this quiz based on the NCERT syllabus?

Absolutely! All questions are carefully crafted based on the NCERT Class 7 Science textbook, Chapter 8: Measurement of Time and Motion, ensuring full syllabus alignment.

What topics does this quiz cover?

This quiz covers historical methods of time measurement, the working of a simple pendulum, the concept of speed, and the distinction between uniform and non-uniform linear motion.

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Review the concepts of time measurement devices, understand the definition of time period for a pendulum, practice speed calculations, and clearly distinguish between uniform and non-uniform motion. Consistent practice with this quiz will help!

Home › CBSE › Class 7 › Science › Measurement of Time and Motion

CBSE · Class 7 · 🔬 Science · Chapter 8

Measurement of Time and Motion

Ancient timekeeping devicesSimple pendulum and time periodSI unit of timeSpeed, distance, and time relationshipUniform and non-uniform motion

This chapter introduces students to the fundamental concepts of time measurement, exploring historical methods like sundials, water clocks, and hourglasses, and the working of a simple pendulum. It also delves into the basics of motion, defining speed, and differentiating between uniform and non-uniform linear motion. Understanding these concepts is crucial for building a strong foundation in physics and observing the world around us.

Ancient Methods of Time Measurement

Sundial: Shadow se time ka pata chalta hai.

Water Clock: Paani ke flow se time measurement.

Hourglass: Sand ke flow se time measure hota hai.

Candle Clock: Jalne wali candle par markings se time ka pata chalta hai.

Purane zamane mein, log time measure karne ke liye natural events par depend karte the jo regularly repeat hote the. Jaise:

Suraj ka nikalna aur doobna: Isse 'din' define hota tha.
Chandrama ke phases: Isse 'mahine' aur 'saal' ka idea milta tha.
Seasons ka change: Isse 'saal' ka concept develop hua.

Time ke chote intervals ko measure karne ke liye, kai devices banaye gaye:

Sundial (धूप घड़ी): Suraj ki shadow ki position change hone se time batata tha. Din mein hi kaam karta tha. [IMAGE: sundial_fig81]
Water Clocks (जल घड़ी): Paani ke flow par based tha.
Ek type mein, marked vessel se paani drip karta tha. [IMAGE: water_clock_fig82]
Dusre type mein, ek floating bowl paani se bhar kar doob jata tha ek fixed time mein.
Hourglass (रेत घड़ी): Sand ke flow se time measure hota tha, ek bulb se dusre bulb mein. [IMAGE: hourglass_fig83]
Candle Clocks (मोमबत्ती घड़ी): Marked candles jalne par time indicate karti thi. [IMAGE: candle_clock_fig84]

Ye sab devices periodic motion ke principle par kaam karte the, jahan ek event fixed interval par repeat hota hai.

❗Important

Ancient timekeeping devices natural periodic events par based the. In devices ne modern clocks ki foundation rakhi.

Understanding a Simple Pendulum

Simple Pendulum ke parts aur oscillatory motion.

Ek simple pendulum ek choti metallic ball (bob) hoti hai jo ek long thread se rigid support se suspend ki hui hoti hai. [IMAGE: simple_pendulum_fig87]

Mean Position (O): Jab pendulum rest par hota hai, toh uski position ko mean position kehte hain.
Extreme Positions (A & B): Jab bob ko ek side move karke release karte hain, toh woh swing karta hai. Jis maximum displacement tak woh jaata hai, woh uski extreme position hoti hai.
Oscillatory Motion: Pendulum ka to-and-fro motion oscillatory motion kehlata hai.
Periodic Motion: Pendulum ka motion periodic hota hai kyunki yeh apne path ko fixed interval of time ke baad repeat karta hai.

One Oscillation Kya Hai?

Ek oscillation complete tab hoti hai jab:

Bob mean position (O) se extreme position (A) tak jaata hai, phir dusri extreme position (B) tak jaata hai, aur wapas mean position (O) par aata hai. (O $\to$ A $\to$ O $\to$ B $\to$ O)
Ya phir, bob ek extreme position (A) se dusri extreme position (B) tak jaata hai, aur wapas usi extreme position (A) par aata hai. (A $\to$ O $\to$ B $\to$ O $\to$ A)

Time Period

Ek oscillation complete karne mein jitna time lagta hai, usse time period kehte hain. Simple pendulum ka time period uski length par depend karta hai, mass par nahi.

📖Definition

Simple Pendulum: Ek choti metallic ball (bob) jo ek long thread se rigid support se suspend ki hui hoti hai.

📖Definition

Time Period: Ek oscillation complete karne mein laga time. Constant length ke pendulum ka time period constant hota hai.

Measuring Time Period of a Pendulum

Huygens' Pendulum Clock: Pendulum ke principle par based.

Pendulum ka time period measure karna ek important experiment hai.

Experiment Setup (Activity 8.2)

Apparatus: String (approx. 150 cm), metallic ball/stone (bob), stopwatch, ruler.
Setup: Bob ko string ke ek end se baandho. Dusre end ko rigid support se fix karo, taaki string ki length approx. 100 cm ho (support aur bob ke beech).
Rest Position: Pendulum ko rest par aane do (mean position).
Initiate Oscillation: Bob ko gently ek side move karke release karo. Push mat karna, bas release karo. String taut honi chahiye.
Measure Time: Stopwatch use karke 10 oscillations complete karne mein laga time record karo.
Repeat: Is activity ko 3-4 baar repeat karo aur readings record karo.

Calculation

Time Period (T) = $\frac{\text{Time taken for 10 oscillations}}{\text{10}}$ seconds

Example Table for Readings:

| S.No. | Time taken for 10 oscillations (seconds) | Time Period (seconds) | Average Time Period (seconds) | | :---: | :--------------------------------------: | :-------------------: | :---------------------------: | | 1 | 20.0 | 2.0 | | | 2 | 20.2 | 2.02 | | | 3 | 19.8 | 1.98 | 2.0 |

Average time period nikalne se readings mein accuracy badhti hai.

Key Observation

Ek given length ke simple pendulum ka time period almost constant hota hai, chahe aap usse kitna bhi chota ya bada swing do (jab tak swing chota ho).
Huygens' Pendulum Clock: Christian Huygens ne 17th century mein pendulum ke is property ka use karke first accurate mechanical clock banaya tha. [IMAGE: huygens_pendulum_clock_fig86]

💡Tip

Pendulum ke time period ko calculate karte waqt, hamesha multiple oscillations (e.g., 10 ya 20) ka time lo aur phir divide karo. Isse measurement error kam hota hai.

Units of Time

Common Clocks and Watches: Time measurement ke modern tools.

Wall Clock: Hour, minute, aur second hands ke saath.

Time ko measure karne ke liye different units use hoti hain:

SI Unit: Time ki SI unit second (s) hai.
Larger Units:
Minute (min): 1 minute = 60 seconds
Hour (h): 1 hour = 60 minutes = 3600 seconds
Day: 1 day = 24 hours
Year: 1 year = 365 days (approx.)

Clocks and Watches

Modern time measurement devices mein clocks aur watches shamil hain. [IMAGE: common_clocks_and_watches_fig88]

Wall Clock: Generally hour, minute, aur second hands hote hain. [IMAGE: wall_clock_fig89]
Wrist Watch: Personal use ke liye.
Digital Watch: Time ko numbers mein display karta hai.
Stopwatch: Short intervals of time ko precisely measure karne ke liye use hota hai, jaise races mein.

Smallest Interval: Ek normal wall clock se hum smallest 1 second ka interval measure kar sakte hain. Scientific experiments mein aur bhi smaller units (millisecond, microsecond) use hoti hain.

❗Important

Time ki SI unit second (s) hai. Unit conversions ko hamesha yaad rakho.

Concept of Slow and Fast Motion

Race mein runners ki speed ka comparison.

Hum daily life mein objects ko 'fast' ya 'slow' move karte hue dekhte hain. Ye comparison kaise karte hain?

Race ka Example: Agar ek race mein kuch log daud rahe hain [IMAGE: different_speeds_in_a_race_fig810]:
Jo runner same time mein sabse zyada distance cover karta hai, woh 'faster' hota hai.
Jo runner same time mein kam distance cover karta hai, woh 'slower' hota hai.

Decision Factor: Distance covered in a given interval of time decide karta hai ki kaun fast hai aur kaun slow.

Speed ka Introduction: Jo object faster move karta hai, uski speed zyada hoti hai. 'Speed' term isi concept ko quantify karta hai.

⭐Remember

Faster object ka matlab hai, usne same time mein zyada distance cover kiya hai, ya phir same distance ko kam time mein cover kiya hai.

Defining and Calculating Speed

Speed ki Definition

Speed = Distance covered by an object in a unit time.

Unit time ka matlab ho sakta hai 1 second, 1 minute, ya 1 hour.

Speed ka Formula

Speed calculate karne ke liye, humein total distance covered aur total time taken pata hona chahiye.

$$ \text{Speed} = \frac{\text{Total Distance Covered}}{\text{Total Time Taken}} $$

Units of Speed

SI Unit: Distance ki SI unit meter (m) hai aur time ki second (s). So, speed ki SI unit hai meter per second (m/s).
Other Common Units: Agar distance kilometer (km) mein aur time hour (h) mein ho, toh speed ki unit kilometer per hour (km/h) hoti hai.

Unit Conversions

km/h to m/s: $1 \text{ km/h} = 1 \times \frac{1000 \text{ m}}{3600 \text{ s}} = \frac{5}{18} \text{ m/s}$
m/s to km/h: $1 \text{ m/s} = 1 \times \frac{3600 \text{ s}}{1000 \text{ m}} = \frac{18}{5} \text{ km/h}$

Average Speed

Aksar objects pure journey mein constant speed se travel nahi karte. Kabhi slow, kabhi fast.
Isliye, jo speed hum calculate karte hain $(\text{Total Distance} / \text{Total Time})$, woh actually average speed hoti hai. Is chapter mein 'speed' term ko 'average speed' ke liye hi use kiya gaya hai.

🧮Formula

$$ \text{Speed} = \frac{\text{Distance}}{\text{Time}} $$

❗Important

Speed ki SI unit m/s hai. Unit conversions ko practice karna bahut zaroori hai.

Relationship Between Speed, Distance, and Time

Speed, distance, aur time ke beech ek fundamental relationship hai, jisse hum ek quantity ko calculate kar sakte hain agar do dusri quantities pata hon:

Speed calculate karna: Agar distance aur time pata ho.

$$ \text{Speed} = \frac{\text{Distance}}{\text{Time}} $$

Distance calculate karna: Agar speed aur time pata ho.

$$ \text{Distance} = \text{Speed} \times \text{Time} $$

Time calculate karna: Agar distance aur speed pata ho.

$$ \text{Time} = \frac{\text{Distance}}{\text{Speed}} $$

Yaad Rakhne ka Tarika (Triangle Method)

Ek triangle banao aur usse teen parts mein divide karo. Top par Distance, bottom left par Speed, aur bottom right par Time likho. Jo quantity find karni hai, usse cover karo, baki do ka relationship formula hoga.

[IMAGE: TODO: Speed-Distance-Time Triangle Diagram]

Distance cover karo $\to$ Speed $\times$ Time
Speed cover karo $\to$ Distance $/$ Time
Time cover karo $\to$ Distance $/$ Speed

Ye relationships numerical problems solve karne mein bahut useful hain.

🧮Formula

$$ \text{Distance} = \text{Speed} \times \text{Time} $$ $$ \text{Time} = \frac{\text{Distance}}{\text{Speed}} $$

💡Tip

Numerical solve karte waqt, hamesha units ko check karo. Saari quantities ek consistent unit system mein honi chahiye (e.g., sab SI units mein ya sab km/h mein).

Uniform and Non-uniform Linear Motion

Uniform aur Non-uniform Motion ka representation.

Motion ko uski speed ke change ke basis par classify kiya ja sakta hai:

Linear Motion

Jab koi object straight line mein move karta hai, toh uske motion ko linear motion kehte hain.

Uniform Linear Motion

Definition: Agar koi object straight line mein constant speed se move karta hai, toh uska motion uniform linear motion kehlata hai.
Characteristic: Uniform motion mein, object equal intervals of time mein equal distances cover karta hai.
Example: Ek car jo empty highway par constant speed se chal rahi hai. [IMAGE: uniform_and_non_uniform_motion_fig811]

Non-uniform Linear Motion

Definition: Agar koi object straight line mein move karta hai, lekin uski speed continuously change hoti rehti hai (badhti ya ghat-ti hai), toh uska motion non-uniform linear motion kehlata hai.
Characteristic: Non-uniform motion mein, object equal intervals of time mein unequal distances cover karta hai.
Example: City traffic mein chal rahi car, jo baar-baar speed badhati aur ghatati hai. [IMAGE: uniform_and_non_uniform_motion_fig811]

Comparison Table:

Example Data (Table 8.3):

| Time (AM) | Train X Position (km) | Train X Distance (km) | Train Y Position (km) | Train Y Distance (km) | | :-------- | :-------------------- | :-------------------- | :-------------------- | :-------------------- | | 10:00 | 0 | 0 | 0 | 0 | | 10:10 | 20 | 20 | 20 | 20 | | 10:20 | 40 | 20 | 35 | 15 | | 10:30 | 60 | 20 | 50 | 15 | | 10:40 | 80 | 20 | 75 | 25 | | 10:50 | 100 | 20 | 95 | 20 | | 11:00 | 120 | 20 | 120 | 25 |

Train X: Har 10 min mein 20 km cover kar rahi hai $\to$ Uniform Motion
Train Y: Har 10 min mein alag-alag distance cover kar rahi hai (15, 25, 20 km) $\to$ Non-uniform Motion

📖Definition

Uniform Motion: Constant speed in a straight line. Equal distances in equal time intervals.

📖Definition

Non-uniform Motion: Changing speed in a straight line. Unequal distances in equal time intervals.

Easy (15)

Which of the following ancient devices used the changing position of a shadow to measure time?
- Water clock
- Sundial (correct)
- Hourglass
- Candle clock
Why: A sundial measures time by observing the shadow cast by the sun.
What is the SI unit of time?
- Minute
- Hour
- Second (correct)
- Day
Why: The second is the standard international unit for measuring time.
The motion of a simple pendulum is an example of which type of motion?
- Random motion
- Circular motion
- Periodic motion (correct)
- Translatory motion
Why: A simple pendulum exhibits periodic motion as it repeats its swing after a fixed interval.
What is the term for the small metallic ball in a simple pendulum?
- Weight
- Bob (correct)
- Mass
- Sphere
Why: The small metallic ball of a pendulum is specifically called the bob.
Which of these devices measures time using the flow of sand?
- Sundial
- Water clock
- Hourglass (correct)
- Candle clock
Why: An hourglass uses sand flowing between two bulbs to measure time.
If an object covers equal distances in equal intervals of time along a straight line, its motion is called:
- Non-uniform motion
- Uniform linear motion (correct)
- Circular motion
- Oscillatory motion
Why: Uniform linear motion means covering equal distances in equal time intervals along a straight line.
What is the formula for calculating speed?
- Speed = Time / Distance
- Speed = Distance × Time
- Speed = Distance / Time (correct)
- Speed = Distance + Time
Why: Speed is calculated by dividing the total distance covered by the total time taken.
Which of the following is NOT an ancient device for measuring time?
- Sundial
- Digital watch (correct)
- Water clock
- Candle clock
Why: Digital watches are modern devices, unlike sundials, water clocks, and candle clocks.
The time taken by a pendulum to complete one oscillation is called its time period.
Why: This statement accurately defines the time period of a simple pendulum.
If an object's speed keeps changing along a straight line, it is in uniform linear motion.
Why: Changing speed in a straight line indicates non-uniform linear motion.
A candle clock measures time by the amount of wax burned.
Why: Candle clocks have markings that indicate time as the candle burns down.
The distance covered by an object in a unit time is called its _________.
Why: Speed is defined as the distance covered per unit of time.
A simple pendulum consists of a small metallic ball suspended from a rigid support by a long _________.
Why: A thread is used to suspend the bob of a simple pendulum.
Identify the device shown in the image, which measures time using the flow of water.
- Sundial
- Water clock (correct)
- Hourglass
- Candle clock
Why: The image shows a water clock, an ancient device that uses water flow to measure time.
What is the device shown in the image, which uses a shadow to indicate time?
- Hourglass
- Water clock
- Sundial (correct)
- Candle clock
Why: The image shows a sundial, which uses the sun's shadow for timekeeping.

Medium (15)

A car travels a distance of 180 km in 3 hours. What is its average speed?
- 50 km/h
- 60 km/h (correct)
- 70 km/h
- 80 km/h
Why: Speed = Distance / Time = 180 km / 3 h = 60 km/h.
If a pendulum completes 20 oscillations in 40 seconds, what is its time period?
- 0.5 seconds
- 1 second
- 2 seconds (correct)
- 4 seconds
Why: Time period = Total time / Number of oscillations = 40 s / 20 = 2 s.
A cyclist covers 100 meters in 20 seconds. What is their speed in m/s?
- 2 m/s
- 5 m/s (correct)
- 10 m/s
- 20 m/s
Why: Speed = Distance / Time = 100 m / 20 s = 5 m/s.
If an object moves at a constant speed of 10 m/s, how much distance will it cover in 5 seconds?
- 2 meters
- 5 meters
- 50 meters (correct)
- 100 meters
Why: Distance = Speed × Time = 10 m/s × 5 s = 50 meters.
Match the ancient time-measuring device with its working principle.
Why: Each device uses a unique physical process for timekeeping.
Match the unit of time with its larger equivalent.
Why: These are standard conversions between different units of time.
Match the type of motion with its description.
Why: Each motion type has a distinct characteristic regarding speed and path.
Match the quantity with its SI unit.
Why: These are the standard international units for these physical quantities.
The motion of a car on a straight road with varying speed is an example of _________ motion.
Why: Varying speed along a straight line defines non-uniform motion.
The total distance covered divided by the total time taken is called the _________ speed.
Why: This formula defines average speed, which accounts for varying speeds during a journey.
A clock that uses the burning of a marked candle to tell time is called a _________ clock.
Why: Candle clocks used the consistent burning rate of candles to measure time.
Arrange the steps to measure the time period of a simple pendulum in the correct order.
Why: The sequence involves setting up, initiating oscillation, timing, and calculating.
Arrange the units of time from smallest to largest.
Why: This is the standard hierarchical order of common time units.
Identify the part of the simple pendulum labeled 'O' in the diagram.
- Extreme position A
- Extreme position B
- Mean position (correct)
- Support point
Why: Point 'O' represents the pendulum's rest or equilibrium position.
The diagram shows a train's motion. Which segment represents uniform linear motion?
- Segment A-B
- Segment B-C (correct)
- Segment C-D
- All segments
Why: The diagram explicitly labels segment B-C as uniform motion.

Hard (10)

Assertion (A): The time period of a simple pendulum remains constant for a given length at a particular place. Reason (R): The time period of a simple pendulum depends on the mass of its bob.
Why: The time period is constant for a given length, but it does not depend on the bob's mass.
Assertion (A): A car moving in city traffic often exhibits non-uniform motion. Reason (R): In city traffic, the car's speed and direction frequently change due to signals, other vehicles, and turns.
Why: City traffic causes frequent changes in speed and direction, leading to non-uniform motion.
Assertion (A): The average speed of an object is calculated as total distance divided by total time. Reason (R): An object always travels at a constant speed throughout its journey.
Why: Average speed is total distance/time, but objects rarely maintain constant speed.
A car travels 120 km in the first 2 hours and then 90 km in the next 1 hour. What is its average speed for the entire journey?
- 50 km/h
- 70 km/h (correct)
- 105 km/h
- 210 km/h
Why: Total distance = 210 km, total time = 3 hours. Average speed = 210/3 = 70 km/h.
A train covers 360 km at a speed of 25 m/s. How much time does it take to complete the journey?
- 4 hours (correct)
- 5 hours
- 6 hours
- 7 hours
Why: Convert speed to km/h (90 km/h), then Time = Distance/Speed = 360/90 = 4 hours.
A runner completes 400 meters in 50 seconds. Another runner completes the same distance in 45 seconds. Which runner has a greater speed and by how much?
- First runner, by 0.89 m/s
- Second runner, by 0.89 m/s (correct)
- First runner, by 1.11 m/s
- Second runner, by 1.11 m/s
Why: Runner 1 speed = 8 m/s, Runner 2 speed = 8.89 m/s. Runner 2 is faster by 0.89 m/s.
The diagram shows a simple pendulum. Which of the following statements about its motion are correct?
- The bob has maximum speed at position O. (correct)
- The bob stops momentarily at position O.
- The bob has maximum potential energy at positions A and B. (correct)
- The time taken to go from A to B is one time period.
Why: Speed is maximum at the mean position (O), and potential energy is maximum at extreme positions (A, B).
Observe the image showing different types of clocks. Which of these clocks would be most suitable for measuring very short time intervals in a sports event?
- Analog wall clock
- Wristwatch
- Digital watch
- Stopwatch (correct)
Why: A stopwatch is designed for precise measurement of specific time durations, ideal for sports.
Which of the following statements correctly describe uniform linear motion?
- The object covers equal distances in equal intervals of time. (correct)
- The speed of the object remains constant. (correct)
- The object's path is always curved.
- The object's acceleration is continuously changing.
Why: Uniform linear motion means constant speed and equal distances in equal times along a straight path.
Consider the following statements about measuring time: 1. Sundials are effective at night. 2. Water clocks were used before mechanical clocks. 3. The time period of a pendulum depends on its length. 4. An hourglass requires electricity to function. Which of these statements are correct?
- 1 and 2
- 2 and 3 (correct)
- 1, 3 and 4
- 2, 3 and 4
Why: Sundials need sunlight, hourglasses don't need electricity. Water clocks predate mechanical ones, and pendulum time period depends on length.