This MCQ module is based on: Motion, Speed and Distance-Time Graphs
TOPIC 29 OF 46
Motion, Speed and Distance-Time Graphs
🎓 Class 7
Science
CBSE
Theory
Ch 8 — Measurement of Time and Motion
⏱ ~14 min
🌐 Language: [gtranslate]
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Who Will Finish First?
Imagine a relay on Sports Day at Prerna's school. The first runner crosses the finish line in 14 seconds, the second in 16, and the third in 18. We instinctively say the first runner is the fastest. But what does "fast" really mean? If a cyclist had covered the same distance in 10 seconds, would she be faster still? To compare motions in a scientific way, we need a single number — and that number is speed.
8.5 Slow or Fast?
When two objects travel the same distance, the one that takes less time is faster. When two objects move for the same time, the one that covers more distance is faster. To combine both ideas into one measurement, we define:
Speed is the distance covered by an object in one unit of time.
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \qquad\text{or}\qquad v = \frac{d}{t} \]
SI unit: metre per second (m/s). A common everyday unit is kilometre per hour (km/h).
To convert between the two units:
\[ 1\,\text{km/h} = \frac{1000\,\text{m}}{3600\,\text{s}} = \frac{5}{18}\,\text{m/s} \]Worked Example — Unit Conversion
A train travels at 72 km/h. What is its speed in m/s?
\[ 72\,\text{km/h} = 72 \times \frac{5}{18}\,\text{m/s} = 20\,\text{m/s} \]So every second, the train rushes through 20 metres of track.
8.6 Uniform and Non-Uniform Motion
Not every journey is the same. A metro train gliding on a long straight stretch covers roughly the same distance every minute. A cyclist weaving through city traffic does not. This difference is captured by two words:
Uniform motion: an object covers equal distances in equal intervals of time — its speed is constant.
Non-uniform motion: an object covers unequal distances in equal intervals of time — its speed keeps changing.
Non-uniform motion: an object covers unequal distances in equal intervals of time — its speed keeps changing.
In real life, uniform motion is the exception, not the rule. A car on a busy road speeds up, slows down, stops at red lights, and creeps in traffic jams. Most motion we see every day is non-uniform.
| Time (s) | Distance – Uniform (m) | Distance – Non-uniform (m) |
|---|---|---|
| 0 | 0 | 0 |
| 1 | 5 | 3 |
| 2 | 10 | 8 |
| 3 | 15 | 18 |
| 4 | 20 | 22 |
| 5 | 25 | 35 |
In the "uniform" column, each row adds 5 m — a constant rate. In the "non-uniform" column, the gap per second keeps changing.
8.7 Distance–Time Graphs
A distance–time graph is a picture of how an object's journey unfolds. Time is plotted on the horizontal axis, distance on the vertical axis.
- Uniform motion — a straight line slanting upwards. Equal rises over equal runs.
- Non-uniform motion — a curved line. The steepness keeps changing.
- At rest — a horizontal line. Time passes but the distance stays the same.
- Slope = speed. The steeper the line, the faster the object.
Activity 8.4 — Plot a Friend's Walk L3 Apply
You will need: a measuring tape, a stopwatch, chalk, a piece of graph paper.
Steps:
- With chalk, mark points at 0 m, 5 m, 10 m, 15 m, 20 m and 25 m along a straight path.
- Ask a friend to start walking at a comfortable, steady pace from the 0-m mark.
- As the friend crosses each chalk mark, record the time shown on the stopwatch.
- Plot Time on the x-axis and Distance on the y-axis. Join the points.
Predict: If the friend walks at constant pace, what shape will the graph have? If she stops for 10 seconds in the middle, how will the graph change?
A steady walk produces an almost perfectly straight slanting line — uniform motion. A 10-second stop appears as a horizontal section in the middle, after which the line starts slanting upward again. The steepness of the slanting part equals the walking speed.
Using the Speed Formula
Starting from \( v = d/t \), we can rearrange to find any one quantity when we know the other two:
\[ d = v \times t \qquad \qquad t = \frac{d}{v} \]
Worked example — average speed.
A car covers 60 km in the first hour, 70 km in the second hour and 50 km in the third hour. Was its motion uniform? Find the average speed.
Each hour's distance is different (60, 70, 50) — the motion is non-uniform.
\[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{60 + 70 + 50}{3} = \frac{180}{3} = 60\,\text{km/h} \]
A car covers 60 km in the first hour, 70 km in the second hour and 50 km in the third hour. Was its motion uniform? Find the average speed.
Each hour's distance is different (60, 70, 50) — the motion is non-uniform.
\[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{60 + 70 + 50}{3} = \frac{180}{3} = 60\,\text{km/h} \]
Average speed is the total distance divided by the total time taken, regardless of whether the motion was uniform in between.
Speed Calculator
Enter any two values and press Calculate. The third value is worked out for you.
Speedometer and Odometer
Every car, bus and motorcycle carries two dials that put these ideas to work.
- The speedometer shows the vehicle's instantaneous speed — how fast it is moving right now, usually in km/h.
- The odometer shows the total distance the vehicle has travelled since it was new — like a running tally on the dashboard.
Competency-Based Questions
A bus leaves Jaipur for Ajmer at 7:00 a.m. In the first hour, it covers 50 km on a clear highway. In the second hour, because of roadworks, it moves only 30 km. In the third hour, back on open road, it covers 60 km. The driver notes each distance on her logbook.
1. Is the motion of the bus uniform or non-uniform? L2
(b) Non-uniform — the bus covers different distances (50, 30, 60 km) in equal one-hour intervals.
2. What is the average speed of the bus over the three-hour journey? L3
Total distance = 50 + 30 + 60 = 140 km. Total time = 3 h. Average speed = 140/3 ≈ 46.7 km/h.
3. Convert 54 km/h to m/s. L2
\(54 \times \dfrac{5}{18} = 15\,\text{m/s}\).
4. On a distance–time graph, a horizontal line represents _______. L1
An object at rest — time passes but distance does not change.
5. Two cars, A and B, are represented on the same distance–time graph. Line A is steeper than line B. What does this tell you? L4
Slope of a distance–time graph equals speed. A steeper line means a larger slope, so car A is moving faster than car B.
Assertion–Reason Questions
Choose: (A) Both true, R explains A. (B) Both true, R does not explain A. (C) A true, R false. (D) A false, R true.
A: A speedometer reading of 60 km/h tells us how fast the car is moving at that instant.
R: A speedometer shows instantaneous speed, not average speed.
(A) — both statements are true, and R correctly explains A.
A: A distance–time graph of an object at rest is a horizontal line.
R: When an object is at rest, its distance from the starting point keeps increasing with time.
(C) — A is true, but R is false. An object at rest has constant distance, not increasing distance.
A: 36 km/h is the same as 10 m/s.
R: To convert km/h to m/s, multiply by 5/18.
(A) — \(36 \times 5/18 = 10\,\text{m/s}\). R is the correct rule and it explains A.
Frequently Asked Questions — Motion, Speed and Distance-Time Graphs
What does the topic 'Motion, Speed and Distance-Time Graphs' cover in Class 7 Science?
The topic 'Motion, Speed and Distance-Time Graphs' is part of NCERT Class 7 Science Chapter 8 — Measurement of Time and Motion. It covers the key ideas of motion, speed, uniform motion, non-uniform motion, distance-time graph, average speed, 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 'Motion, Speed and Distance-Time Graphs' important for Class 7 NCERT Science?
'Motion, Speed and Distance-Time Graphs' 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 motion 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 Motion, Speed and Distance-Time Graphs?
The key concepts in 'Motion, Speed and Distance-Time Graphs' for Class 7 Science are: motion, speed, uniform motion, non-uniform motion, distance-time graph, average speed. 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 Motion, Speed and Distance-Time Graphs taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Motion, Speed and Distance-Time Graphs' 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.
What real-life examples of motion can Class 7 students observe at home?
Class 7 students can observe motion at home in many simple ways linked to 'Motion, Speed and Distance-Time Graphs'. Kitchens, school bags, playgrounds and the night sky are full of examples that connect to NCERT Chapter 8 — Measurement of Time and Motion. For instance, students can check labels on food and cleaning products, watch changes while cooking, or observe the Sun and Moon across a week. Keeping a small science diary — noting the date, what was observed and a quick sketch — turns everyday life into a science lab. These real-life connections make concepts stick and prepare students well for competency-based questions in CBSE Class 7 Science.
How does 'Motion, Speed and Distance-Time Graphs' connect to other chapters of Class 7 Science?
'Motion, Speed and Distance-Time Graphs' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of motion 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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