This MCQ module is based on: Time and Motion
TOPIC 30 OF 46
Time and Motion
🎓 Class 7
Science
CBSE
Theory
Ch 8 — Measurement of Time and Motion
⏱ ~8 min
🌐 Language: [gtranslate]
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Chapter 8 Summary
Time is measured using events that repeat at steady intervals — from the shadow of a sundial to the vibrations of caesium atoms inside an atomic clock. The SI unit of time is the second. A simple pendulum — a bob on a thread — swings to and fro with a time period that depends only on the length of the thread. Motion is described by speed, defined as the distance travelled per unit time: \( v = d/t \). Motion is uniform when equal distances are covered in equal times, and non-uniform otherwise. A distance–time graph gives a picture of how a journey unfolds: straight slanting lines for uniform motion, curves for non-uniform motion, and horizontal segments for rest.
Key Terms
Periodic eventAn event that repeats at regular intervals of time.
Second (s)SI unit of time.
Simple pendulumA heavy bob hung from a light thread, free to swing.
OscillationOne full to-and-fro swing of a pendulum.
Time period (T)Time taken for one oscillation. Unit: second.
Frequency (f)Number of oscillations per second. Unit: hertz (Hz). \(f = 1/T\).
SpeedDistance travelled per unit time. \(v = d/t\).
Uniform motionEqual distances covered in equal time intervals.
Non-uniform motionUnequal distances in equal time intervals.
Average speedTotal distance ÷ total time.
SpeedometerInstrument that reads instantaneous speed.
OdometerInstrument that records total distance travelled.
NCERT Exercises — Solutions
Q1Identify and describe the parts of a simple pendulum.
A simple pendulum has three essential parts:
(i) Rigid support — a firm fixed point (such as a clamp stand or the edge of a table) from which the pendulum hangs. It must not move.
(ii) Thread (or string) — a light, inextensible thread whose upper end is tied to the support. Its length decides how fast the pendulum swings.
(iii) Bob — a small, heavy object (metal ball, washer, or similar) tied to the lower end of the thread. It is the part that actually swings to and fro.
(i) Rigid support — a firm fixed point (such as a clamp stand or the edge of a table) from which the pendulum hangs. It must not move.
(ii) Thread (or string) — a light, inextensible thread whose upper end is tied to the support. Its length decides how fast the pendulum swings.
(iii) Bob — a small, heavy object (metal ball, washer, or similar) tied to the lower end of the thread. It is the part that actually swings to and fro.
Q2Define the following: (a) oscillation, (b) time period, (c) frequency.
(a) Oscillation: one complete to-and-fro movement of the pendulum bob — from one extreme position, through the mean position, to the other extreme, and back again.
(b) Time period (T): the time taken by the pendulum to complete one full oscillation. Its SI unit is the second (s).
(c) Frequency (f): the number of oscillations that occur in one second. Its unit is hertz (Hz). Time period and frequency are related by \( f = 1/T \).
(b) Time period (T): the time taken by the pendulum to complete one full oscillation. Its SI unit is the second (s).
(c) Frequency (f): the number of oscillations that occur in one second. Its unit is hertz (Hz). Time period and frequency are related by \( f = 1/T \).
Q3Name different units of time.
Common units of time include:
• Second (s) — the SI unit.
• Minute (min) = 60 s
• Hour (h) = 60 min = 3600 s
• Day = 24 h = 86 400 s
• Week = 7 days; Month ≈ 30 days; Year ≈ 365 days
Smaller units include millisecond (10⁻³ s), microsecond (10⁻⁶ s) and nanosecond (10⁻⁹ s).
• Second (s) — the SI unit.
• Minute (min) = 60 s
• Hour (h) = 60 min = 3600 s
• Day = 24 h = 86 400 s
• Week = 7 days; Month ≈ 30 days; Year ≈ 365 days
Smaller units include millisecond (10⁻³ s), microsecond (10⁻⁶ s) and nanosecond (10⁻⁹ s).
Q4What kind of distance–time graph is obtained for an object in (i) uniform motion and (ii) non-uniform motion?
(i) Uniform motion: a straight line slanting upward. Equal distances are covered in equal time intervals, so the line has a constant slope (= speed).
(ii) Non-uniform motion: a curved line. The slope changes from point to point because the speed keeps changing.
(ii) Non-uniform motion: a curved line. The slope changes from point to point because the speed keeps changing.
Q5The speed of an object is given by \( v = d/t \). Using this, convert 72 km/h into m/s.
We use the conversion factor \(1\,\text{km/h} = \dfrac{5}{18}\,\text{m/s}\).
\[ 72\,\text{km/h} = 72 \times \frac{5}{18}\,\text{m/s} = \frac{360}{18} = 20\,\text{m/s} \]
So the object covers 20 metres every second.
Q6Compare the three modes of time measurement — sundial, pendulum clock and quartz watch.
| Feature | Sundial | Pendulum clock | Quartz watch |
|---|---|---|---|
| Working principle | Shadow of rod cast by Sun | Regular swing of a pendulum | Vibrations of a quartz crystal |
| Usable anytime? | Only during sunny daytime | Day and night | Anytime, anywhere |
| Accuracy | Low (to nearest 5–10 min) | Good (to seconds per day) | Very high (fractions of a second) |
| Portability | Fixed in place | Wall-mounted, heavy | Wrist-sized, portable |
| Age | Ancient (~1500 BCE) | Since 17th century | Since 20th century |
Q7List the instruments used to measure time and speed.
For time: wall clock, wrist watch, pendulum clock, quartz watch, atomic clock, stopwatch (mechanical or digital), sundial, water clock, sand clock, candle clock.
For speed: the speedometer in a vehicle measures instantaneous speed in km/h. Scientists also use radar guns, photo-gates in laboratories, and GPS-based speed meters in mobile phones. The related odometer (in cars) measures the total distance travelled, from which average speed can be calculated.
For speed: the speedometer in a vehicle measures instantaneous speed in km/h. Scientists also use radar guns, photo-gates in laboratories, and GPS-based speed meters in mobile phones. The related odometer (in cars) measures the total distance travelled, from which average speed can be calculated.
Q8A car covers 60 km in the first hour, 70 km in the second hour, and 50 km in the third hour. Is the motion uniform? Justify your answer. Find the average speed of the car.
The distances covered in equal one-hour intervals are 60 km, 70 km and 50 km. Since these are not equal, the car does not cover equal distances in equal times. Therefore the motion is non-uniform.
\[ \text{Total distance} = 60 + 70 + 50 = 180\,\text{km} \]
\[ \text{Total time} = 3\,\text{h} \]
\[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{180}{3} = 60\,\text{km/h} \]
Q9Which type of motion is more common in daily life — uniform or non-uniform? Give three examples from your experience to support your answer.
Non-uniform motion is far more common in daily life. True uniform motion requires a constant speed and a straight path, which is rare outside carefully controlled situations.
Three everyday examples of non-uniform motion:
1. A city bus — it speeds up after a stop, slows down at traffic lights, and halts at every stand, so it covers unequal distances in equal minutes.
2. A child on a swing — fastest at the bottom, slowest at the two ends, so its speed keeps changing.
3. A stone dropped from a rooftop — it speeds up every second as it falls under gravity, covering more distance each second than the one before.
(Examples of nearly uniform motion, for contrast, include a train gliding on a long straight track at cruising speed or the tip of the second hand of a clock.)
Three everyday examples of non-uniform motion:
1. A city bus — it speeds up after a stop, slows down at traffic lights, and halts at every stand, so it covers unequal distances in equal minutes.
2. A child on a swing — fastest at the bottom, slowest at the two ends, so its speed keeps changing.
3. A stone dropped from a rooftop — it speeds up every second as it falls under gravity, covering more distance each second than the one before.
(Examples of nearly uniform motion, for contrast, include a train gliding on a long straight track at cruising speed or the tip of the second hand of a clock.)
Q10Data for the motion of an object is given in the table below. State whether the speed of the object is uniform or non-uniform. Find the average speed.
| Time (s) | 0 | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|---|
| Distance (m) | 0 | 8 | 16 | 24 | 32 | 40 |
Look at the distance covered in each 2-second interval:
0 → 2 s: 8 m | 2 → 4 s: 8 m | 4 → 6 s: 8 m | 6 → 8 s: 8 m | 8 → 10 s: 8 m.
Every equal time interval shows the same distance (8 m), so the motion is uniform. \[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{40\,\text{m}}{10\,\text{s}} = 4\,\text{m/s} \] For uniform motion, the average speed equals the (constant) speed of the object.
0 → 2 s: 8 m | 2 → 4 s: 8 m | 4 → 6 s: 8 m | 6 → 8 s: 8 m | 8 → 10 s: 8 m.
Every equal time interval shows the same distance (8 m), so the motion is uniform. \[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{40\,\text{m}}{10\,\text{s}} = 4\,\text{m/s} \] For uniform motion, the average speed equals the (constant) speed of the object.
Q11A vehicle moves along a straight road and covers a distance of 2 km. In the first 500 m it moves with a speed of 10 m/s, and in the next 500 m with a speed of 5 m/s. If the whole journey is completed in 200 s, what is the average speed of the vehicle for the entire journey?
Given: Total distance = 2 km = 2000 m. Total time = 200 s.
(The speeds in the first two 500-m stretches are extra information — they describe how the journey began, but for the overall average speed we need only the total distance and total time.) \[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{2000\,\text{m}}{200\,\text{s}} = 10\,\text{m/s} \] In km/h: \(10 \times 18/5 = 36\,\text{km/h}\).
Check the first two stretches: time for the first 500 m = 500/10 = 50 s. Time for the next 500 m = 500/5 = 100 s. Together these take 150 s, leaving 200 − 150 = 50 s for the remaining 1000 m — an average of 20 m/s over that last kilometre. The journey is clearly non-uniform, but its overall average speed is 10 m/s.
(The speeds in the first two 500-m stretches are extra information — they describe how the journey began, but for the overall average speed we need only the total distance and total time.) \[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{2000\,\text{m}}{200\,\text{s}} = 10\,\text{m/s} \] In km/h: \(10 \times 18/5 = 36\,\text{km/h}\).
Check the first two stretches: time for the first 500 m = 500/10 = 50 s. Time for the next 500 m = 500/5 = 100 s. Together these take 150 s, leaving 200 − 150 = 50 s for the remaining 1000 m — an average of 20 m/s over that last kilometre. The journey is clearly non-uniform, but its overall average speed is 10 m/s.
Frequently Asked Questions — Time and Motion — Chapter 8 Exercises
What does the topic 'Time and Motion — Chapter 8 Exercises' cover in Class 7 Science?
The topic 'Time and Motion — Chapter 8 Exercises' is part of NCERT Class 7 Science Chapter 8 — Measurement of Time and Motion. It covers the key ideas of time, motion, speed, pendulum, graphs, NCERT exercises, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.
Why is 'Time and Motion — Chapter 8 Exercises' important for Class 7 NCERT Science?
'Time and Motion — Chapter 8 Exercises' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 8 — Measurement of Time and Motion — introduces time and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.
What are the key concepts students should remember from Time and Motion — Chapter 8 Exercises?
The key concepts in 'Time and Motion — Chapter 8 Exercises' for Class 7 Science are: time, motion, speed, pendulum, graphs, NCERT exercises. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 8 will help students retain these concepts for unit tests and the annual CBSE examination.
How is Time and Motion — Chapter 8 Exercises taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Time and Motion — Chapter 8 Exercises' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 8 — Measurement of Time and Motion — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.
How should Class 7 students prepare for the Chapter 8 exercises?
To prepare for the Chapter 8 — Measurement of Time and Motion — exercises in NCERT Class 7 Science, students should first revise the theory in Parts 1–3 and make a short list of definitions and diagrams for time, motion, speed, pendulum, graphs, NCERT exercises. Next, attempt each exercise question on their own before checking the solution. Pay extra attention to MCQs, assertion–reason questions and short-answer items, as these appear in CBSE competency-based tests. Practising with the NCERT Curiosity textbook, the exemplar questions, and the MyAiSchool practice bank helps Class 7 students score better in unit tests and the annual examination.
How does 'Time and Motion — Chapter 8 Exercises' connect to other chapters of Class 7 Science?
'Time and Motion — Chapter 8 Exercises' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of time appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 8 — Measurement of Time and Motion — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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