Motion and Measurement of Distances – Class 6 Science (Notes & Questions Answers)
NCERT Class 6 Science Chapter 10 | Simple notes + complete Q&A (7 MCQs, 7 Very Short, 7 Short, 7 Long). Designed for quick revision, exam readiness, and a smooth reading experience.
Easy Notes: Motion and Measurement of Distances
1) Why do we measure?
Measurement helps us compare and communicate sizes and distances accurately. In early times, people used non-standard units like cubit (elbow to fingertips), handspan, and footstep. These varied from person to person, causing confusion. To avoid mismatch, the world moved to standard units so everyone measures in the same way.
2) Standard Units and SI Unit of Length
The internationally accepted system is the SI (International System of Units). The SI unit of length is the metre (m). Common sub-units and larger units:
- 1 kilometre (km) = 1000 metres (m)
- 1 metre (m) = 100 centimetres (cm)
- 1 centimetre (cm) = 10 millimetres (mm)
We use different units according to context: kilometres for long distances, metres for room lengths, centimetres for small objects, and millimetres for very tiny differences.
3) Tools for Measuring Length
- Ruler/Metre scale: straight objects such as books, pencils, or desks.
- Measuring tape: flexible tape for larger lengths like rooms and fields.
- Thread and ruler: for curved lines—first trace with thread, then measure the thread.
4) Precautions while Measuring
- Zero alignment: Keep object’s edge at the zero mark. If the zero is worn, start from another mark and subtract.
- Eye position (avoid parallax): Keep eye vertically above the marking to read correctly.
- Scale placement: Keep the scale along the length, not tilted or bent.
- No gaps: For accurate results, ensure no gap between scale and object.
- Record unit: Always write value with unit, e.g., 12.4 cm, not just 12.4.
5) Motion and Rest
An object is in motion if its position changes with time; it is at rest if position does not change with time with respect to a chosen reference. Rest or motion is always described relative to something (for example, a book on a table is at rest with respect to the table).
6) Types of Motion (with examples)
- Rectilinear motion: along a straight line (a train on a straight track).
- Circular motion: around a fixed point (tip of a clock’s second hand).
- Rotational motion: the whole object spins about an axis (a spinning top or a rotating globe).
- Periodic motion: repeats at equal intervals (swing of a simple pendulum).
- Oscillatory motion: to and fro about a mean position (swinging of a child’s swing).
- Random/irregular motion: changes direction frequently (tiny pollen grains moving in water).
7) Fast and Slow (Idea of Speed)
If two objects cover different distances in the same time, the one covering more distance is faster. If two objects take different times to cover the same distance, the one taking less time is faster. You will study formulas later; for now, compare by distance covered or time taken.
8) Story of Transport (very brief)
From carts and boats to cycles, cars, trains, planes, and rockets—transport has improved steadily. With better transport, people travel farther in less time and exchange goods and ideas more easily.
9) Common Mistakes in Measurement
- Starting from the scale’s edge instead of the zero mark.
- Reading with a slanted eye position causing parallax error.
- Ignoring the unit or mixing units without converting.
- Measuring a curved line directly with a straight scale (use thread first).
Questions & Answers – Chapter 10
This section includes 7 MCQs (with choices), 7 Very Short, 7 Short, and 7 Long questions with clear answers.
📝 A) Multiple Choice Questions (Choose the correct option)
1. The SI unit of length is:
(a) centimetre (b) metre (c) kilometre (d) millimetre
Correct answer: (b) metre
2. Which tool is best to measure the length of a classroom wall?
(a) 15 cm ruler (b) compass (c) measuring tape (d) protractor
Correct answer: (c) measuring tape
3. To measure a curved line on paper, you should first use:
(a) divider (b) thread (c) magnifying glass (d) set square
Correct answer: (b) thread
4. Keeping the eye vertically above the mark while reading a scale helps avoid:
(a) friction (b) refraction (c) parallax error (d) reflection
Correct answer: (c) parallax error
5. Motion of the tip of a minute hand of a clock is an example of:
(a) rectilinear motion (b) circular motion (c) random motion (d) oscilla
6. The value equal to 1 metre is:
(a) 10 cm (b) 100 cm (c) 1000 cm (d) 100 mm
Correct answer: (b) 100 cm
7. A child on a swing shows:
(a) translational motion (b) rotational motion (c) oscillatory motion (d) circular motion
Correct answer: (c) oscillatory motion
🧩 B) Very Short Answer Questions
1. Define measurement.
Ans: Measurement is the comparison of an unknown quantity with a known standard unit.
2. State the SI unit of length.
Ans: Metre (m).
3. What is parallax error?
Ans: Error that occurs when the eye is not placed vertically above the scale marking while reading.
4. Name one device used for measuring long distances in a room.
Ans: Measuring tape.
5. Give one example of rectilinear motion.
Ans: A car moving along a straight road.
6. Which unit will you use to express the thickness of a coin?
Ans: Millimetre (mm).
7. How will you measure a curved line?
Ans: Trace it with a thread, then measure the thread with a ruler.
✍️ C) Short Answer Questions
1. Why are standard units necessary?
Ans: Non-standard units like handspan vary from person to person, leading to confusion. Standard units (SI) ensure that measurements are uniform and comparable everywhere.
2. List any three precautions for accurate measurement with a ruler.
Ans: (i) Align the object with the zero mark, (ii) keep the scale along the length, (iii) keep eye vertically above the mark to avoid parallax.
3. Distinguish between circular and rotational motion with examples.
Ans: In circular motion, a point or part of an object moves around a fixed center (tip of a clock hand). In rotational motion, the whole object spins about its axis (a spinning globe).
4. A pencil is measured starting from the 1 cm mark because the zero is worn out. The end coincides with 12.2 cm. What is the length?
Ans: Length = 12.2 − 1.0 = 11.2 cm.
5. What is periodic motion? Give two examples.
Ans: Motion that repeats at equal time intervals, e.g., a pendulum swing, the revolution of Earth around the Sun.
6. Which unit will you choose for measuring the distance between two cities and why?
Ans: Kilometre, because the distance is large and kilometres are convenient for long lengths.
7. Explain why we prefer a measuring tape over a ruler for measuring a round table’s edge.
Ans: A measuring tape is flexible and can follow the curved surface; a rigid ruler cannot bend to fit the curve.
🧠 D) Long Answer Questions
1. Describe the evolution from non-standard to standard units and how it improved daily life.
Ans: Early measurements used body parts such as cubit, handspan, and footstep. These varied widely, causing disputes in trade and construction. Adoption of the SI system with metre as the unit of length made values uniform and reliable. Builders, shopkeepers, and students could now communicate exact sizes, reducing confusion and improving fairness and safety in practical work.
2. Explain, step by step, how you would measure the length of a curved path drawn on paper.
Ans: (i) Take a thin thread and place it carefully along the curved line without gaps. (ii) Mark the end point on the thread with a pen. (iii) Straighten the thread gently on a ruler, aligning one end with the zero. (iv) Read the marking at the pen mark with your eye vertically above it. (v) Record the value along with unit (e.g., 14.6 cm). Repeat once to confirm.
3. Discuss types of motion with at least two examples for each type mentioned in this chapter.
Ans: Rectilinear: a bus on a straight road, a ball rolling straight along a corridor. Circular: tip of a ceiling fan blade, the rim of a rotating bicycle wheel. Rotational: a spinning top, a globe turning about its axis. Periodic/Oscillatory: swing of a pendulum, the movement of a seesaw. Random: motion of tiny particles suspended in water. Recognizing types helps us choose suitable measuring tools and describe movement precisely.
4. What is parallax error? How can we avoid it in school measurements?
Ans: Parallax error is a reading mistake that occurs when the observer’s eye is not vertical to the scale. The reading appears shifted due to angle. To avoid: (i) place the scale flat against the object, (ii) ensure the eye is straight above the mark, (iii) take two readings and agree on the value, (iv) use a sharp pencil mark at the edge to guide the eye. These steps improve accuracy in practical work.
5. A student measured a table edge and wrote “120”. Explain why this is incomplete and how to correct it. Also state any two precautions for such measurements.
Ans: The value is incomplete because it lacks a unit; without a unit it has no clear meaning. Correct form is, for example, 120 cm. Precautions: start from the scale’s zero or correct for worn zero; keep the scale aligned with the edge; avoid parallax by proper eye position.
6. Why is it better to repeat a measurement and take the same value twice before recording the final reading?
Ans: Repeating reduces the effect of small mistakes due to hand movement, scale placement, or eye position. If two readings match, we gain confidence that the value is close to the true length. If they differ, we re-measure carefully to find the correct one. This habit improves reliability in science.
7. Compare rectilinear, circular, and oscillatory motion on the basis of path, direction change, and examples.
Ans: Rectilinear: path is straight; direction remains same unless turned; e.g., toy car on a straight track. Circular: path is a circle around a center; direction continuously changes while speed may be constant; e.g., second hand of a clock. Oscillatory: to and fro about a mean position; direction reverses after each swing; e.g., a playground swing. Understanding differences helps choose terms correctly in answers.
Prepared for quick learning and exam readiness. Keep practicing!
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