NCERT Solutions for Class 6 Science (Curiosity) Chapter 5: Measurement of Length and Motion

These Class 6 Science Curiosity Chapter 5 solutions cover Measurement of Length and Motion from the new NCF textbook (2026–27). The chapter explains why we need standard units, how to use the SI unit of length (metre) correctly, how to measure straight and curved lines, the idea of a reference point, and the three basic types of motion — linear, circular and oscillatory. All 13 “Let us enhance our learning” questions are answered, with worked unit conversions, activity guidance and labelled teaching diagrams.

Class: 6 Subject: Science Book: Curiosity Chapter: 5 Topic: Measurement of Length and Motion Session: 2026–27
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Class 6 Science Curiosity Chapter 5 Solutions – Overview

Chapter 5 of Curiosity, Measurement of Length and Motion, follows Deepa and her friends as they try to measure the length of their classroom table using handspans. Because everyone’s handspan is a different size, they get different numbers — showing why the world needs standard units. The chapter introduces the International System of Units (SI), whose unit of length is the metre (m), along with the kilometre, centimetre and millimetre and the relations between them. It teaches the correct way to use a scale (contact, eye position, broken-end method), how to measure a curved line with a thread, the idea of a reference point for describing position, and how an object is in motion or at rest relative to that point. Finally it classifies motion as linear, circular and oscillatory.

Key Concepts & Definitions

Measurement: comparing an unknown length with a known fixed quantity called a unit. Every measurement has two parts — a number and a unit (e.g. 13 handspans).

Why standard units: body parts like handspan, foot and finger differ from person to person, so the same length gives different readings. A standard unit has the same agreed size for everyone. Small reading differences can still arise from the instrument or measurement method.

SI unit of length: the metre (m) is the SI unit of length. Useful relations: 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm (and 1 mm = 0.1 cm).

Choosing a scale: use a 15-cm scale for small objects (pencil, eraser), a metre scale or measuring tape for a room, and a flexible tape or thread for curved lengths (girth of a tree, chest).

Correct way to measure: place the scale in contact along the object; keep the eye directly above the mark; if the zero end is broken, use any full mark and subtract its reading from the reading at the other end.

Reference point: a fixed object or point with respect to which the position (distance) of another object is stated — e.g. a kilometre stone gives your distance from a city.

Motion and rest: an object is in motion if its position changes with respect to a reference point with time; it is at rest if its position does not change.

Types of motion: Linear (along a straight line), Circular (along a circular path), and Oscillatory (to and fro about a fixed position). Circular or oscillatory motion is periodic when the motion repeats at equal time intervals, as in an ideal steadily turning wheel or regularly swinging pendulum.

An object spans 1.0 cm to 10.4 cm on a ruler; its length is 9.4 cm.
Broken-end method: end reading minus start reading. Tap to view at full size.

Let us enhance our learning — NCERT Solutions

Questions 1–13 follow NCERT Curiosity Chapter 5, pages 97–99. Answers and diagrams are original ClearStudy teaching aids. Activity measurements are examples, not observations to copy.

1. Some lengths are given in Column I of Table 5.5. Some units are given in Column II. Match the lengths with the units suitable for measuring those lengths.

Column IColumn II
Distance between Delhi and Lucknowcentimetre
Thickness of a coinkilometre
Length of an erasermetre
Length of school groundmillimetre
ANSWER We pick the unit whose size suits the length being measured.
Column I (length)Suitable unit
Distance between Delhi and Lucknowkilometre (km)
Thickness of a coinmillimetre (mm)
Length of an erasercentimetre (cm)
Length of school groundmetre (m)

2. Read the following statements and mark True (T) or False (F) against each. (i) The motion of a car moving on a straight road is an example of linear motion. (ii) Any object which is changing its position with respect to a reference point with time is said to be in motion. (iii) 1 km = 100 cm

ANSWER (i) True (T). A car on a straight road moves along a straight line, so its motion is linear motion. (ii) True (T). This is exactly the definition of motion — a change of position with respect to a reference point with time. (iii) False (F). The correct relation is 1 km = 1000 m = 1,00,000 cm, not 100 cm.

3. Which of the following is not a standard unit of measuring length? (i) millimetre (ii) centimetre (iii) kilometre (iv) handspan

ANSWER (iv) handspan. Millimetre, centimetre and kilometre are standard SI-based units that give the same value for everyone. A handspan differs from person to person, so it is not a standard unit.

4. Search for the different scales or measuring tapes at your home and school. Find out the smallest value that can be measured using each of these scales. Record your observations in a tabular form.

ANSWER This is an activity. Look at the smallest division marked on each scale and write it as the smallest value (least count). Sample observation table:
Measuring deviceSmallest value that can be measured
15-cm geometry-box scale1 mm (0.1 cm)
Metre scale1 mm
Tailor’s measuring tape1 mm (0.1 cm)
Long steel measuring tape1 mm
These are example values only. Inspect your own devices: if 1 cm is divided into 10 equal intervals, each is 1 mm. Count intervals, not just the printed lines. Some tapes or rulers have different divisions.

5. Suppose the distance between your school and home is 1.5 km. Express it in metres.

ANSWER We use 1 km = 1000 m. 1.5 km = 1.5 × 1000 m = 1500 m.

6. Take a tumbler or a bottle. Measure the length of the curved part of the base of glass or bottle and record it.

ANSWERWrap a non-stretching thread once around the outside of the base. Mark the starting point and the point where one complete turn ends. Do not stretch the thread.Remove and straighten it, then measure the marked length with a ruler or measuring tape. If using a 15-cm ruler for a longer thread, measure in consecutive sections without gaps or overlaps and add the lengths. Record your actual result in centimetres; it is the base’s circumference.

7. Measure the height of your friend and express it in (i) metres (ii) centimetres and (iii) millimetres.

ANSWER This is an activity. Suppose the measured height of your friend is 1.4 m. Then, using 1 m = 100 cm and 1 cm = 10 mm: (i) 1.4 m (ii) 1.4 m × 100 = 140 cm (iii) 140 cm × 10 = 1400 mm Write the actual height you measure and convert it the same way.

8. You are given a coin. Estimate how many coins are required to be placed one after the other lengthwise, without leaving any gap between them, to cover the whole length of the chosen side of a notebook. Verify your estimate by measuring the same side of the notebook and the size of the coin using a 15-cm scale.

ANSWER This is an estimation activity. First guess the number, then check it by measuring. Sample working: suppose the side of the notebook = 24 cm and the diameter of the coin = 2 cm. Number of coins = length of notebook side ÷ diameter of one coin = 24 cm ÷ 2 cm = 12 coins. Compare this calculated number with your first estimate to see how close your guess was.
If the division is not a whole number: record the approximate result. To cover the entire side with whole coins, round up; the last coin may extend beyond the edge. For a notebook longer than the ruler, measure consecutive sections carefully.

9. Give two examples each for linear, circular and oscillatory motion.

ANSWER Linear motion: (i) a car moving on a straight road; (ii) an apple falling straight down from a tree. Circular motion: (i) a stone tied to a thread and whirled in a circle; (ii) the tip of a clock hand moving round the dial. Oscillatory motion: (i) a swing moving to and fro; (ii) the pendulum (bob) of a wall clock swinging side to side.

10. Observe different objects around you. It is easier to express the lengths of some objects in mm, some in cm and some in m. Make a list of three objects in each category and enter them in the Table 5.6.

ANSWER Choose the unit whose size matches the object. Sample answer:
SizeObjects
mmThickness of a coin, thickness of an eraser, length of an ant
cmLength of a pencil, length of a notebook, length of a spoon
mHeight of a door, length of a classroom, height of a person

11. A rollercoaster track is made in the shape shown in Fig. 5.19. A ball starts from point A and escapes through point F. Identify the types of motion of the ball on the rollercoaster and corresponding portions of the track.

ANSWERAB and EF: linear motion, because these portions are straight.The looped portion BCDE: circular motion in the exercise’s school-level classification. The ball follows the loop instead of a straight line. The connecting bends are curved; a curved path is not necessarily an exact circle.The ball does not move to and fro about a fixed position, so its single trip from A to F is not oscillatory or periodic. The diagram below keeps the exercise labels so each part can be located.
Rollercoaster schematic labelled A to F: straight AB and EF; looped portion BCDE.
Q11: match the type of motion to the labelled track portion. Tap to view at full size.

12. Tasneem wants to make a metre scale by herself. She considers the following materials for it—plywood, paper, cloth, stretchable rubber and steel. Which of these should she not use and why?

ANSWERShe should not use stretchable rubber, because stretching changes the spacing between its marks. Ordinary cloth can also stretch, shrink or fray, making it unsuitable for a reliable homemade metre scale.Steel or stable plywood are better choices. Paper needs firm backing and protection from moisture or tearing. Flexibility itself is not the problem: a good tailor’s tape bends around curves but resists stretching.

13. Think, design and develop a card game on conversion of units of length to play with your friends.

ANSWER This is a creative activity. A simple design: make pairs of cards where one card shows a length in one unit and its matching card shows the same length in another unit — for example “2 m” pairs with “200 cm”, “1 km” pairs with “1000 m”, and “5 cm” pairs with “50 mm”. How to play: shuffle all cards and place them face down. Each player turns over two cards; if the two cards show the same length in different units, the player keeps the pair and gets a point; if not, they turn the cards back. The player with the most correct pairs wins. This is like a “memory match” game and helps practise the conversions 1 km = 1000 m, 1 m = 100 cm and 1 cm = 10 mm.

Common Mistakes to Avoid

Watch out for these

  • Writing a measurement as just a number — always include the unit (e.g. write “1500 m”, not “1500”).
  • Mixing up conversions — remember 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm (so 1 km = 1,00,000 cm).
  • Reading a scale with the eye at an angle — keep the eye directly above the mark, or the reading is wrong (parallax error).
  • Starting measurement from the broken/worn zero end — use a clear full mark and subtract it from the reading at the other end.
  • Treating a handspan, foot or finger as a standard unit — they differ from person to person.
  • Confusing rest and motion — always state motion or rest with respect to a reference point.
  • Calling oscillatory motion “circular” — a swing or pendulum moves to and fro, not round and round.

Extra Practice Questions

These questions and MCQs are ClearStudy practice, separate from the NCERT exercise.

Short Answer Type Questions

Q1. What is the SI unit of length and what is its symbol?

ANSWERThe SI unit of length is the metre and its symbol is m.

Q2. Why do we need standard units of measurement?

ANSWERBody-based units such as handspan and foot differ from person to person, giving different readings for the same length. Standard units give everyone the same agreed reference, so measurements can be compared. Careful technique is still needed.

Q3. What is a reference point?

ANSWERA reference point is a fixed object or point with respect to which the position or distance of another object is stated, for example a kilometre stone showing distance from a city.

Q4. How do you measure the length of a curved line?

ANSWERPlace a thread along the curved line, mark its two ends, then straighten the thread and measure its length with a metre scale. A flexible measuring tape can also be used directly.

Q5. Convert 250 cm into metres.

ANSWER1 m = 100 cm, so 250 cm = 250 ÷ 100 = 2.5 m.

Long Answer Type Questions

Q1. When the friends measured the table with their handspans, they got different numbers. Explain why this happened and what it teaches us.

ANSWEREach person used their own handspan as the unit, but everyone’s handspan is a different size — when the friends placed their handspans side by side, the lengths did not match. Because the unit itself was different for each person, the number of handspans for the same table came out different (13, 14, slightly more, slightly less). This shows that a measurement made with a body part cannot be relied upon by others. It teaches us that we need standard units — like the metre — which have an agreed size. Different people can then compare readings, while checking for measurement errors. That is exactly why people use scales and measuring tapes instead of body parts.

Q2. Explain linear, circular and oscillatory motion with one example each, and state which of them are periodic.

ANSWERLinear motion is motion along a straight line — for example, a car moving on a straight road. Circular motion is motion along a circular path — for example, a stone whirled in a circle at the end of a thread. Oscillatory motion is to-and-fro motion about a fixed position — for example, a swing or a pendulum. If a motion repeats its path after a fixed interval of time it is called periodic. The chapter uses regular circular and oscillatory motions as examples. They are periodic when the motion repeats at equal time intervals; following a circle once is not sufficient. A single straight-line journey is not periodic.

Q3. Padma sees kilometre stones reading “Delhi 70 km” and then “Delhi 60 km”. Explain, using the idea of reference point and motion, what this tells us.

ANSWERA kilometre stone states a distance with respect to a fixed place, so here Delhi is the reference point. The first stone tells Padma that her position is 70 km from Delhi, and the next one tells her she is 60 km from Delhi. Since her distance from the reference point has changed with time (from 70 km to 60 km), her position is changing, which means she is in motion. The decreasing distance also tells her she is getting closer to Delhi (her destination). This shows how a reference point lets us describe position and decide whether an object is moving.

MCQs & Assertion–Reason

1. The SI unit of length is:

(a) centimetre    (b) metre    (c) kilometre    (d) handspan

2. Which of the following is correct?

(a) 1 m = 10 cm    (b) 1 km = 100 m    (c) 1 cm = 10 mm    (d) 1 cm = 100 mm

3. 2.5 km is equal to:

(a) 250 m    (b) 2500 m    (c) 25 m    (d) 25000 m

4. A handspan is not a standard unit because:

(a) it is too small    (b) it cannot measure cloth    (c) it differs from person to person    (d) it is too large

5. The correct position of the eye while reading a scale is:

(a) to the left of the mark    (b) to the right of the mark    (c) directly above the mark    (d) far away from the scale

6. To measure the girth of a tree, the most suitable device is a:

(a) metre scale    (b) 15-cm scale    (c) flexible measuring tape    (d) wooden rod

7. A swing moving to and fro is an example of:

(a) linear motion    (b) circular motion    (c) oscillatory motion    (d) no motion

8. An object is said to be in motion if, with time, its position with respect to a reference point:

(a) stays the same    (b) changes    (c) disappears    (d) doubles

9. Using a scale with a broken zero end, the length of an object reading from 1.0 cm to 10.4 cm is:

(a) 10.4 cm    (b) 11.4 cm    (c) 9.4 cm    (d) 1.0 cm

10. Which pair can show periodic motion when repeated at equal time intervals?

(a) linear and circular    (b) circular and oscillatory    (c) linear and oscillatory    (d) only linear

Answer key: 1-(b), 2-(c), 3-(b), 4-(c), 5-(c), 6-(c), 7-(c), 8-(b), 9-(c), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Standard units like the metre are needed for measuring length.

Reason: Body-based units such as handspan differ from person to person.

A-R 2. Assertion: A swing shows circular motion.

Reason: A swing moves to and fro about a fixed position.

A-R 3. Assertion: Whether an object is at rest or in motion depends on the reference point chosen.

Reason: An object is in motion only if its position changes with respect to a reference point with time.

A-R 4. Assertion: 1 km is equal to 100 cm.

Reason: 1 km = 1000 m and 1 m = 100 cm.

A-R 5. Assertion: A flexible measuring tape or a thread is used to measure a curved line.

Reason: A rigid metre scale cannot bend to follow a curved path.

Answer key: 1-(A), 2-(D), 3-(A), 4-(D), 5-(A).

Quick Revision Summary

  • A measurement has two parts: a number and a unit.
  • Body parts are not standard units; the SI unit of length is the metre (m).
  • 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm (and 1 mm = 0.1 cm).
  • Measure correctly: scale in contact, eye directly above the mark; for a broken end, subtract the start reading from the end reading.
  • Measure curved lines with a thread or flexible tape.
  • A reference point is a fixed point used to state position; an object is in motion if its position changes with respect to it with time, else at rest.
  • Types of motion: linear (straight line), circular (circular path), oscillatory (to and fro). Regular circular and oscillatory motions are periodic when they repeat at equal time intervals.

How to write a clear answer

Learn the conversion chain km → m → cm → mm by heart and always write the unit with the number. In motion questions, never forget to mention the reference point. For “type of motion” questions, match the path to the right word — straight line = linear, circular path = circular, to-and-fro = oscillatory — and check whether the motion repeats at equal time intervals before calling it periodic. For measuring questions, mention correct scale placement, eye position and the broken-end (subtraction) method to explain your method clearly.

Frequently Asked Questions

What is Class 6 Science Curiosity Chapter 5 about?

Chapter 5, Measurement of Length and Motion, explains why we need standard units, the SI unit of length (the metre) and its conversions, the correct way to use a scale, how to measure curved lines, the idea of a reference point, and the three types of motion — linear, circular and oscillatory.

What is the SI unit of length and the main conversions?

The SI unit of length is the metre (m). The key conversions are 1 km = 1000 m, 1 m = 100 cm and 1 cm = 10 mm (so 1 mm = 0.1 cm).

What are the three types of motion in this chapter?

Linear motion (along a straight line), circular motion (along a circular path) and oscillatory motion (to and fro about a fixed position). Regular circular and oscillatory motion are periodic when the motion repeats at equal time intervals.

Are these Class 6 Science Curiosity Chapter 5 solutions free?

Yes. All solutions are free and follow the official NCERT Curiosity textbook for session 2026–27.

Source: NCERT Curiosity Chapter 5 (official PDF). Diagrams are schematic teaching aids; use a real ruler for measurements.

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