Measurement of Length and Motion – Important Questions and Answers
Premium CBSE Class 6 Science revision post on Measurement of Length and Motion. This post covers measurement using body parts, standard units, SI unit of length, correct way of measuring length, curved line measurement, reference point, rest and motion, linear motion, circular motion, oscillatory motion, periodic motion, important questions, case studies, HOTS, FAQs, and an interactive quiz.
Short Introduction
Measurement is an important part of science and daily life. We measure cloth, height, distance, length of objects and even curved paths. Earlier, people used body parts such as handspan, foot, fingers and strides to measure length, but such units vary from person to person. Therefore, standard units such as metre, centimetre, millimetre and kilometre are used. This chapter also explains how to describe the position of an object using a reference point and how to classify motion as linear, circular and oscillatory.
Chapter Overview
Need for Measurement
Measurement helps us compare lengths and express them using a number and a unit.
Standard Units
Standard units avoid confusion because they remain the same for everyone.
SI Unit of Length
The SI unit of length is metre. Its symbol is m.
Correct Measurement
The scale should touch the object along its length and the eye should be directly above the mark being read.
Reference Point
A reference point is a fixed point used to describe the position of an object.
Types of Motion
Motion can be linear, circular or oscillatory depending on the path followed by the object.
Important Formula and Concept Box
Example: 13 handspans, 15 cm, 2 m.
Kilometre is used for large distances.
Metre is the SI unit of length.
Millimetre is used for very small lengths.
An object is in motion if its position changes with respect to a reference point.
Important Keywords with Meanings
| Keyword | Meaning |
|---|---|
| Measurement | The process of finding the size, length, distance or quantity of something. |
| Length | The distance between two ends of an object. |
| Unit | A fixed quantity used for measuring something. |
| Handspan | The distance between the tip of the thumb and the tip of the little finger when the hand is fully stretched. |
| Balisht | A traditional name for handspan. |
| Angula | A traditional unit based on finger width. |
| Standard unit | A unit accepted and used by everyone to avoid confusion. |
| SI units | International System of Units used worldwide as standard units. |
| Metre | The SI unit of length; symbol is m. |
| Centimetre | A smaller unit of length; 1 m = 100 cm. |
| Millimetre | A very small unit of length; 1 cm = 10 mm. |
| Kilometre | A larger unit of length; 1 km = 1000 m. |
| Measuring tape | A flexible tool used for measuring lengths, curved surfaces and body measurements. |
| Metre scale | A scale used to measure length in metres and centimetres. |
| Reference point | A fixed point with respect to which position or distance is described. |
| Position | The location of an object with respect to a reference point. |
| Rest | A body is at rest if its position does not change with time with respect to a reference point. |
| Motion | A body is in motion if its position changes with time with respect to a reference point. |
| Linear motion | Motion along a straight line. |
| Circular motion | Motion along a circular path. |
| Oscillatory motion | To and fro motion about a fixed position. |
| Periodic motion | Motion that repeats after a fixed interval of time. |
Very Short Answer Questions
1. What is measurement?
Answer: Measurement is the process of finding the size, length or distance of something using a unit.
2. What are the two parts of a measurement?
Answer: A measurement has two parts: a number and a unit.
3. Give one example of measurement using a body part.
Answer: Measuring a table using handspan is an example.
4. What is handspan?
Answer: Handspan is the distance between the tip of the thumb and the tip of the little finger when the hand is fully stretched.
5. What is balisht?
Answer: Balisht is another name for handspan.
6. Why are body-part units not reliable?
Answer: They are not reliable because they differ from person to person.
7. What are standard units?
Answer: Standard units are fixed units accepted and used by everyone.
8. What is the full form of SI units?
Answer: SI stands for International System of Units.
9. What is the SI unit of length?
Answer: The SI unit of length is metre.
10. What is the symbol of metre?
Answer: The symbol of metre is m.
11. How many centimetres are there in 1 metre?
Answer: 1 metre has 100 centimetres.
12. How many millimetres are there in 1 centimetre?
Answer: 1 centimetre has 10 millimetres.
13. How many metres are there in 1 kilometre?
Answer: 1 kilometre has 1000 metres.
14. Which unit is suitable for measuring the distance between two cities?
Answer: Kilometre is suitable.
15. Which unit is suitable for measuring the length of an eraser?
Answer: Centimetre is suitable.
16. Which tool is suitable for measuring the girth of a tree?
Answer: A flexible measuring tape is suitable.
17. What is a reference point?
Answer: A reference point is a fixed point used to describe the position of an object.
18. When is an object said to be in motion?
Answer: An object is in motion if its position changes with time with respect to a reference point.
19. When is an object said to be at rest?
Answer: An object is at rest if its position does not change with time with respect to a reference point.
20. What is linear motion?
Answer: Motion along a straight line is called linear motion.
21. What is circular motion?
Answer: Motion along a circular path is called circular motion.
22. What is oscillatory motion?
Answer: To and fro motion about a fixed position is called oscillatory motion.
23. What is periodic motion?
Answer: Motion that repeats after a fixed interval of time is called periodic motion.
24. Give one example of oscillatory motion.
Answer: Motion of a swing is an example of oscillatory motion.
Short Answer Questions
1. Why did different students get different handspan measurements for the same table?
Answer: They got different measurements because the size of handspan differs from person to person. Therefore, body-part units are not reliable for accurate measurement.
2. Why do we need standard units?
Answer: We need standard units because body-based units such as handspan, foot and fingers vary from person to person. Standard units give the same measurement everywhere and avoid confusion.
3. What is meant by SI units?
Answer: SI units mean International System of Units. These are standard units accepted and used by different countries for scientific and daily measurements.
4. Write the relation between kilometre, metre, centimetre and millimetre.
Answer: 1 km = 1000 m, 1 m = 100 cm and 1 cm = 10 mm.
5. Why is a flexible measuring tape used by tailors?
Answer: A flexible measuring tape bends easily around the body and curved surfaces. Therefore, it is suitable for measuring chest size, waist size and curved body measurements.
6. What is the correct way to place a scale while measuring length?
Answer: The scale should be placed in contact with the object along its length. It should not be tilted or kept away from the object.
7. What is the correct position of the eye while reading a scale?
Answer: The eye should be directly above the mark to be read. This avoids wrong readings due to viewing from the side.
8. How can we measure length using a broken scale?
Answer: If the zero mark is broken, start from another clear mark such as 1 cm. Note the reading at the other end and subtract the starting reading from it.
9. How can the length of a curved line be measured?
Answer: The length of a curved line can be measured using a flexible measuring tape or by placing a thread along the curve and then measuring the straightened thread with a scale.
10. Why should we write the unit with every measurement?
Answer: A measurement is incomplete without a unit. For example, writing only 15 is unclear, but 15 cm clearly shows the measured length.
11. What is a reference point? Give an example.
Answer: A reference point is a fixed point used to describe position. For example, a kilometre stone saying “Delhi 70 km” uses Delhi as the reference point.
12. Why is reference point important in deciding rest and motion?
Answer: Rest and motion depend on the reference point. A passenger is at rest with respect to the bus but in motion with respect to a building outside the bus.
13. Give two examples of linear motion.
Answer: A falling eraser and students marching in a straight line are examples of linear motion.
14. Give two examples of circular motion.
Answer: Motion of a merry-go-round and an eraser tied to a thread and whirled around are examples of circular motion.
15. Give two examples of oscillatory motion.
Answer: Motion of a swing and motion of a metal strip moving up and down are examples of oscillatory motion.
Long Answer Questions
1. Explain why body-part units are not suitable for accurate measurement.
Answer: Body-part units such as handspan, foot, finger width and stride were used in olden times. However, these units differ from person to person. For example, if five students measure the length of the same table using their handspans, their answers may be different because their handspans are different. Therefore, body-part units are not suitable for accurate and uniform measurement. This is why standard units such as metre, centimetre and kilometre are used.
2. Write a note on standard units and SI units.
Answer: Different systems of units were used in different parts of the world in earlier times. This created confusion when people travelled, traded or communicated across regions. To avoid this, countries adopted standard units. The system now used worldwide is called the International System of Units or SI units. The SI unit of length is metre and its symbol is m. Standard units make measurement uniform and reliable.
3. Explain the commonly used units of length with conversions.
Answer: The commonly used units of length are kilometre, metre, centimetre and millimetre.
- Kilometre: Used for large distances such as distance between cities. 1 km = 1000 m.
- Metre: SI unit of length. Used for room height, cloth length and playground length.
- Centimetre: Used for small objects such as pencil, eraser and notebook.
- Millimetre: Used for very small lengths such as thickness of a coin.
4. Describe the correct method of measuring length using a scale.
Answer: To measure length correctly:
- Select a suitable scale according to the object.
- Place the scale in contact with the object along its length.
- Do not place the scale in a slanting position.
- Align one end of the object with the zero mark of the scale.
- Keep the eye directly above the other end of the object while reading.
- Write the reading with the correct unit.
5. How do you measure length if the zero mark of a scale is broken?
Answer: If the zero mark of the scale is broken or unclear, we can use another clear mark such as 1 cm or 2 cm. Place one end of the object at this mark. Read the scale at the other end of the object. Subtract the starting reading from the final reading. For example, if one end is at 1.0 cm and the other end is at 10.4 cm, then length = 10.4 cm − 1.0 cm = 9.4 cm.
6. Explain how to measure the length of a curved line.
Answer: A straight scale cannot measure a curved line directly. To measure a curved line, take a thread and carefully place it along the curved path. Mark the beginning and end points on the thread. Then straighten the thread and measure its length using a scale. A flexible measuring tape can also be used for measuring curved lines and curved surfaces.
7. Explain reference point with the example of kilometre stones.
Answer: A reference point is a fixed point used to describe the position or distance of an object. Kilometre stones on roads show distance from a fixed place. For example, if a stone reads “Delhi 70 km”, it means the position is 70 km from Delhi. Here, Delhi is the reference point. As a person moves closer to Delhi, the distance written on kilometre stones decreases.
8. Explain rest and motion with the example of passengers in a bus.
Answer: Rest and motion depend on the reference point. Passengers sitting inside a moving bus do not change their position with respect to the bus, so they are at rest with respect to the bus. But their position changes with respect to trees, buildings or poles outside the bus, so they are in motion with respect to objects outside. This shows that reference point is important in deciding whether an object is at rest or in motion.
9. Differentiate between linear, circular and oscillatory motion.
| Type of Motion | Meaning | Example |
|---|---|---|
| Linear motion | Motion along a straight line. | A falling eraser, march-past, pushed box. |
| Circular motion | Motion along a circular path. | Merry-go-round, whirling eraser tied to a thread. |
| Oscillatory motion | To and fro motion about a fixed position. | Swing, hanging eraser, vibrating metal strip. |
10. What is periodic motion? Explain with examples.
Answer: If an object repeats its path after a fixed interval of time, its motion is called periodic motion. Circular motion and oscillatory motion are periodic in nature because they repeat again and again. Examples include motion of a merry-go-round, motion of a swing and motion of an object whirled in a circular path.
Case-Study Based Questions
Case Study 1: Measuring the Table
Deepa and her friends measured the same table using their handspans. Anish got slightly more than 13 handspans, Padma got 13, Tasneem got slightly less than 13, Deepa got between 13 and 14, and Hardeep got 14.
Q1. Why were their answers different?
Answer: Their answers were different because their handspans were of different sizes.
Q2. What does this show about body-part units?
Answer: Body-part units are not reliable for accurate measurement.
Q3. Which type of unit should be used instead?
Answer: Standard units such as metre or centimetre should be used.
Case Study 2: Broken Scale
A student measures a pencil using a broken scale. One end of the pencil is at 2.0 cm and the other end is at 14.5 cm.
Q1. Can the broken scale still be used?
Answer: Yes, it can be used if clear marks are available.
Q2. What is the length of the pencil?
Answer: Length = 14.5 cm − 2.0 cm = 12.5 cm.
Q3. What precaution is important while reading the scale?
Answer: The eye should be directly above the mark being read.
Case Study 3: Kilometre Stones
Padma is travelling by bus to Delhi. One kilometre stone reads “Delhi 70 km” and later another reads “Delhi 60 km”.
Q1. What do the kilometre stones indicate?
Answer: They indicate the distance from Delhi.
Q2. What is the reference point in this case?
Answer: Delhi is the reference point.
Q3. How did Padma know she was getting closer to Delhi?
Answer: The distance decreased from 70 km to 60 km.
Case Study 4: Passengers in a Bus
Deepa sees that passengers inside the bus remain seated on the same seats. But when she looks outside, buildings and trees seem to move backward.
Q1. Are the passengers at rest or in motion with respect to the bus?
Answer: They are at rest with respect to the bus.
Q2. Are the passengers in motion with respect to a building outside?
Answer: Yes, they are in motion with respect to the building.
Q3. What concept does this explain?
Answer: It explains the importance of reference point in deciding rest and motion.
Case Study 5: Children’s Park
In a children’s park, a child slides down a slide, another child sits on a swing, and a merry-go-round rotates.
Q1. What type of motion is shown by the child moving down a straight slide?
Answer: Linear motion.
Q2. What type of motion is shown by the swing?
Answer: Oscillatory motion.
Q3. What type of motion is shown by the merry-go-round?
Answer: Circular motion.
Assertion-Reason Questions
Choose the correct option:
A. Both Assertion and Reason are true and Reason is the correct explanation.
B. Both Assertion and Reason are true but Reason is not the correct explanation.
C. Assertion is true but Reason is false.
D. Assertion is false but Reason is true.
1. Assertion: Handspan is not a standard unit. Reason: Handspan differs from person to person.
Answer: A
2. Assertion: The SI unit of length is metre. Reason: Its symbol is m.
Answer: B
3. Assertion: 1 km = 1000 m. Reason: Kilometre is used for measuring large distances.
Answer: B
4. Assertion: A flexible tape is useful for measuring the girth of a tree. Reason: It can bend around curved surfaces.
Answer: A
5. Assertion: The eye should be directly above the mark being read. Reason: This helps avoid error in reading.
Answer: A
6. Assertion: A measurement is complete without a unit. Reason: A unit tells what standard has been used for measurement.
Answer: D
7. Assertion: Delhi can be a reference point for kilometre stones showing distance from Delhi. Reason: A reference point is a fixed point used to describe position.
Answer: A
8. Assertion: A passenger can be at rest and in motion at the same time with respect to different reference points. Reason: Rest and motion depend on the reference point.
Answer: A
9. Assertion: Motion along a straight line is called circular motion. Reason: Circular motion happens along a circular path.
Answer: D
10. Assertion: Motion of a swing is oscillatory. Reason: A swing moves to and fro about a fixed position.
Answer: A
Competency-Based and Critical Thinking / HOTS Questions
1. Why is it better to measure cloth with a metre scale or measuring tape instead of handspan?
Answer: A metre scale or measuring tape uses standard units, so the result is the same for everyone. Handspan differs from person to person, so it may give different results.
2. A tailor uses a flexible tape, but a shopkeeper uses a metal rod to measure cloth. Why?
Answer: A metal rod is useful for measuring straight lengths of cloth. A flexible tape is better for measuring body parts because it can bend around curved surfaces.
3. Why should we not use stretchable rubber to make a metre scale?
Answer: Stretchable rubber changes its length when pulled. A scale must have fixed markings, so stretchable rubber is not suitable.
4. A notebook side is longer than a 15-cm scale. How can you measure it?
Answer: Measure in parts. Mark the point up to 15 cm, then shift the scale carefully and measure the remaining length. Add all parts to get the total length.
5. How can you estimate the thickness of one page of a notebook?
Answer: Measure the thickness of many pages together, such as 100 pages, and divide the total thickness by the number of pages. This gives the approximate thickness of one page.
6. If a bus is moving but the passengers appear still, are they really still?
Answer: They are still with respect to the bus, but they are moving with respect to objects outside the bus. So, rest and motion depend on reference point.
7. Why does a ball on a rollercoaster track show more than one type of motion?
Answer: A rollercoaster track can have straight, curved and circular parts. The ball may show linear motion on straight portions and circular or curved motion on curved portions.
8. A student writes the length of a pencil as “12”. What is wrong?
Answer: The unit is missing. The correct answer should include a unit, such as 12 cm.
9. Why are circular and oscillatory motions called periodic in many cases?
Answer: They repeat their path after a fixed interval of time. For example, a swing moves to and fro again and again, and a merry-go-round repeats its circular path.
10. Why is a reference point needed to describe position accurately?
Answer: Without a reference point, the position of an object is unclear. A fixed reference point tells us from where the distance or position is being described.
Diagram-Based Questions
Diagram 1: Unit Conversion Ladder
Question: Convert 1.5 km into metres.
Answer: 1.5 km = 1.5 × 1000 m = 1500 m.
Diagram 2: Correct Eye Position
Correct
Eye directly above the mark.
Incorrect
Eye viewed from left or right side.
Question: Why should the eye be directly above the mark?
Answer: To avoid wrong reading due to side viewing.
Diagram 3: Broken Scale Reading
Question: What formula is used?
Answer: Length = final reading − initial reading.
Diagram 4: Reference Point
Question: What is the reference point?
Answer: Delhi is the reference point.
Diagram 5: Types of Motion
Linear
Straight path
Circular
Circular path
Oscillatory
To and fro
Question: Which type of motion is shown by a swing?
Answer: Oscillatory motion.
Quick Revision Box
- Measurement has two parts: number and unit.
- Handspan, foot, finger width and stride are body-based units.
- Body-based units differ from person to person.
- Standard units give uniform measurement.
- SI unit of length is metre.
- Symbol of metre is m.
- 1 km = 1000 m.
- 1 m = 100 cm.
- 1 cm = 10 mm.
- Use kilometre for large distances.
- Use centimetre or millimetre for small lengths.
- A flexible measuring tape is useful for curved surfaces.
- The scale must be placed along the length of the object.
- The eye must be directly above the mark being read.
- If zero mark is broken, subtract starting reading from final reading.
- A curved line can be measured using thread or flexible tape.
- Reference point is a fixed point used to describe position.
- Motion means change in position with time with respect to a reference point.
- Rest means no change in position with time with respect to a reference point.
- Motion along a straight line is linear motion.
- Motion along a circular path is circular motion.
- To and fro motion about a fixed position is oscillatory motion.
- Motion that repeats after a fixed interval is periodic motion.
Important Exam Tips
Interactive Quiz
Choose the correct answer and click submit.
Frequently Asked Questions
1. What is measurement?
Measurement is the process of finding the size, length or distance of something using a unit.
2. Why are standard units needed?
Standard units are needed because body-based units differ from person to person and can create confusion.
3. What is the SI unit of length?
The SI unit of length is metre. Its symbol is m.
4. How do we measure a curved line?
A curved line can be measured using a flexible measuring tape or by placing a thread along the curve and then measuring the thread.
5. What is a reference point?
A reference point is a fixed point used to describe the position or distance of an object.
6. What is motion?
An object is in motion if its position changes with time with respect to a reference point.
7. What is rest?
An object is at rest if its position does not change with time with respect to a reference point.
8. What is linear motion?
Motion along a straight line is called linear motion.
9. What is circular motion?
Motion along a circular path is called circular motion.
10. What is oscillatory motion?
To and fro motion about a fixed position is called oscillatory motion.
Final Conclusion
The chapter Measurement of Length and Motion teaches students how to measure lengths correctly using standard units and proper tools. It also explains why reference points are important in describing position, rest and motion. By understanding linear, circular and oscillatory motion, students can identify different types of motion in daily life and build a strong foundation for higher science.
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