Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
NCERT Solutions for Class 6 Science Chapter 10 — Motion and Measurement of Distances
Key Concepts at a Glance
| Term | Definition |
|---|---|
| Measurement | The comparison of an unknown quantity with a known fixed quantity (unit) |
| Unit | A known fixed quantity used for measurement; e.g., metre for length, kilogram for mass |
| SI Unit | International System of Units — the standard system of measurement used worldwide |
| Metre (m) | The SI unit of length; defined as the standard unit for measuring distance |
| Motion | A change in the position of an object with respect to time |
| Rectilinear motion | Motion along a straight line — e.g., a car moving on a straight road |
| Circular motion | Motion along a circular path — e.g., the hands of a clock, blades of a fan |
| Periodic motion | Motion that repeats itself after regular intervals of time — e.g., a pendulum |
| Rotational motion | Motion in which an object spins around a fixed axis — e.g., a spinning top |
| Oscillatory motion | To-and-fro motion about a fixed point — e.g., a swing, a pendulum |
| Parallax error | Error in measurement caused by viewing the scale from an angle instead of straight on |
| Least count | The smallest measurement that can be taken accurately with a given scale |
Intext Questions (with Answers)
Intext Question 1 (Page 106)
Give two examples each, of modes of transport used on land, water, and air.
| Medium | Examples |
|---|---|
| Land | Bus, train, car, bicycle |
| Water | Boat, ship, steamer |
| Air | Aeroplane, helicopter |
Intext Question 2 (Page 107)
Fill in the blanks:
(a) One metre is \_\_\_\_\_\_ cm.
(b) Five kilometre is \_\_\_\_\_\_ m.
(c) Motion of a child on a swing is \_\_\_\_\_\_.
(d) Motion of the needle of a sewing machine is \_\_\_\_\_\_.
(e) Motion of wheel of a bicycle is \_\_\_\_\_\_.
Intext Question 3 (Page 108)
Why can a pace or a footstep not be used as a standard unit of length?
A pace or a footstep cannot be used as a standard unit of length because:
1. Different people have different stride lengths — a tall person's step is longer than a short person's step. 2. No uniformity — the same person may take different-length steps at different times. 3. Lack of consistency — pace length varies with speed, terrain, fatigue, and health. 4. Cannot be reproduced exactly — different measurements by different people would give different results.
A standard unit must be the same everywhere and for everyone. The metre is defined precisely and does not change from person to person.
Intext Question 4 (Page 110)
What precaution should be taken while measuring the length of an object using a scale? List at least three.
The following precautions should be taken while measuring length with a scale:
1. Place the scale along the length of the object — the scale should be in full contact with the object's edge, not at an angle. 2. Correct eye position — the eye should be directly above the point of measurement. Looking from an angle causes parallax error. 3. Start from zero — ensure that the zero mark of the scale is at one end of the object. If the zero mark is worn out, use any other convenient mark and subtract. 4. Use correct units — note the least count of the scale and record the measurement in proper units.
Intext Question 5 (Page 111)
What is the smallest measurement that can be measured accurately by a scale you use in your school? What is it called?
The smallest measurement that can be measured accurately by a school scale is 1 mm (one millimetre). This is called the least count of the scale. The least count is the smallest division on the scale and determines the precision of measurement.
In a standard 15 cm school ruler:
- 1 cm is divided into 10 equal parts
- Each small division = 1 mm = 0.1 cm
- Least count = 1 mm = 0.1 cm
Intext Question 6 (Page 112)
What type of motion do the following objects have?
(a) A spinning top
(b) A swing
(c) A moving wheel of a bicycle
(d) The Earth revolving around the Sun
(e) A falling stone
Intext Question 7 (Page 113)
While measuring the length of a knitting needle, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?
Length of the needle = Final reading − Initial reading
Length = 33.1 cm − 3.0 cm = 30.1 cm
Note: When the zero mark is not used, we subtract the initial reading from the final reading. This method avoids errors from worn-out zero marks.
Intext Question 8 (Page 113)
Write the similarity and dissimilarity between the motion of a bicycle and a ceiling fan.
| Bicycle | Ceiling Fan | |
|---|---|---|
| Similarity | The wheel shows circular motion — each point on the wheel moves in a circular path around the axle | The blades show circular motion — each point on the blade moves in a circular path around the centre |
| Dissimilarity | The bicycle also moves forward (rectilinear motion) — it goes from one place to another | The ceiling fan does not move from one place to another — it remains fixed at one point and only rotates |
Intext Question 9 (Page 114)
Why could you not use an elastic measuring tape to measure distance? What would be some problems you would meet in telling someone about a distance you measured with an elastic tape?
An elastic measuring tape stretches when pulled and returns to its original shape when released. This creates several problems:
1. Different readings each time — The length measured depends on how much the tape is stretched. Two people pulling with different force would get different measurements. 2. No standard unit — A unit must be fixed and unchanging. An elastic tape changes length, so it cannot define a consistent unit. 3. Cannot be reproduced — The same distance measured twice may give different values. 4. Confusing communication — If you tell someone "the distance is 5 tape-lengths," they would not know how much the tape was stretched each time.
For these reasons, only rigid, non-stretchable measuring instruments should be used.
Intext Question 10 (Page 114)
Give two examples of periodic motion.
1. Pendulum — A pendulum swings to and fro, completing each oscillation in the same time interval. 2. A child on a swing — The child moves back and forth, repeating the motion at regular intervals.
Other examples: the heartbeat, the ticking of a clock, vibrating string of a guitar.
Exercise Questions (with Answers)
Exercise Question 1
Give two examples each of the following types of motion:
(a) Rectilinear motion
(b) Circular motion
(c) Periodic motion
Exercise Question 2
Which of the following are correct statements?
(a) The SI unit of length is kilometre.
(b) The standard unit of measurement is accepted everywhere.
(c) Motion of a car on a straight road is an example of rectilinear motion.
(d) Motion of a swing is an example of circular motion.
Exercise Question 3
Classify the following as rectilinear, circular, or periodic motion:
(a) Motion of a train on a straight bridge
(b) Motion of a child on a merry-go-round
(c) Motion of blades of a fan
(d) Motion of a pendulum
(e) Motion of a stone dropped from a height
(f) Motion of a wheel of a moving cycle
Exercise Question 4
How many centimetres make a kilometre?
1 kilometre = 1000 metres 1 metre = 100 centimetres
Therefore, 1 kilometre = 1000 × 100 = 1,00,000 centimetres (1 lakh cm)
Exercise Question 5
What is the difference between rectilinear and circular motion? Give two examples of each.
| Feature | Rectilinear Motion | Circular Motion |
|---|---|---|
| Definition | Motion along a straight line | Motion along a circular path |
| Direction | Same direction throughout | Direction changes continuously |
| Path | Straight line | Circle |
| Examples | Car on straight road, falling ball | Ceiling fan blades, clock hands |
Exercise Question 6
The distance between Radha's home and her school is 3250 m. Express this distance in kilometres.
1 kilometre = 1000 metres
Distance in kilometres = 3250 ÷ 1000 = 3.250 km (or 3.25 km)
Exercise Question 7
While measuring the length of a pencil, the scale was placed such that its 2.0 cm mark coincided with one end and the other end read 15.3 cm. Find the length of the pencil.
Length of the pencil = Final reading − Initial reading
Length = 15.3 cm − 2.0 cm = 13.3 cm
Exercise Question 8
Why is it important to use standard units of measurement?
Standard units of measurement are important because:
1. Uniformity — Everyone gets the same result regardless of who measures. 2. Accuracy — Standard units are precisely defined and do not vary. 3. Communication — Scientists, engineers, and people around the world can understand and compare measurements. 4. Reproducibility — The same measurement can be repeated and verified anywhere. 5. Avoid confusion — Non-standard units (hand span, footstep) vary from person to person, causing errors and misunderstandings.
The SI system (International System of Units) is the globally accepted standard.
Exercise Question 9 (MCQ)
Which of the following types of motion is shown by a spinning wheel?
(a) Rectilinear motion ✗ (b) Circular motion ✓ (c) Periodic motion ✗ (d) None of these ✗
A spinning wheel rotates around its axis, and each point on the wheel moves in a circular path.
Exercise Question 10 (MCQ)
Which unit is most suitable for measuring the distance between two cities?
(a) Millimetre ✗ (b) Centimetre ✗ (c) Metre ✗ (d) Kilometre ✓
The distance between two cities is usually hundreds of kilometres. Using millimetre, centimetre, or metre would result in very large and inconvenient numbers.
Multiple Choice Questions (MCQs)
MCQ 1
1 metre = 100 centimetres = 1000 millimetres.
MCQ 2
Which of the following is a standard unit of length?
(a) Hand span ✗ (b) Footstep ✗ (c) Metre ✓ (d) Arm length ✗
Hand span, footstep, and arm length vary from person to person. The metre is the internationally accepted SI unit of length.
MCQ 3
The motion of a planet around the Sun is:
(a) Rectilinear ✗ (b) Circular ✓ (c) Oscillatory ✗ (d) Random ✗
Planets revolve around the Sun in nearly circular (actually elliptical) orbits.
MCQ 4
Parallax error occurs when:
(a) The scale is too short ✗ (b) The eye is not directly above the measurement mark ✓ (c) The object is too small ✗ (d) The scale is bent ✗
Parallax error occurs when the eye is at an angle to the scale instead of being directly above it, causing an incorrect reading.
MCQ 5
Which type of motion does a pendulum show?
(a) Rectilinear ✗ (b) Circular ✗ (c) Periodic ✓ (d) Random ✗
A pendulum swings to and fro, repeating its motion at regular time intervals — this is periodic motion.
MCQ 6
The distance between two cities is 85 km. This is equal to:
(a) 8500 m ✗ (b) 85000 m ✓ (c) 850000 m ✗ (d) 850 m ✗
85 km = 85 × 1000 = 85,000 m.
Common Mistakes
1. Confusing circular and periodic motion: Not all periodic motion is circular. A pendulum is periodic but moves in an arc (oscillatory), not a full circle. A ceiling fan blade is circular but not periodic (it keeps rotating, not repeating a back-and-forth motion).
2. Forgetting to subtract the initial reading: When a scale is used starting from a mark other than zero (e.g., starting at 2.0 cm), students often write the final reading directly as the length. The correct length = Final reading − Initial reading.
3. Incorrect unit conversions: Common errors include writing 1 m = 10 cm (it is 100 cm) or 1 km = 100 m (it is 1000 m). Memorise: 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm.
4. Using body parts as standard units: Hand span, footstep, and arm length vary from person to person. They cannot be used as standard units. Always use SI units for measurement.
5. Ignoring parallax error: Reading the scale from an angle instead of directly above the mark leads to incorrect measurements. Always keep the eye directly above the point being measured.
Exam Checklist
- [ ] Can you define measurement and explain why standard units are needed?
- [ ] Can you convert between km, m, cm, and mm correctly?
- [ ] Can you list at least 3 precautions while measuring length with a scale?
- [ ] Can you identify and give examples of rectilinear, circular, and periodic motion?
- [ ] Can you calculate length when the initial reading is not zero?
- [ ] Can you explain what parallax error is and how to avoid it?
- [ ] Can you state the SI unit of length and its relation to other units?
- [ ] Can you distinguish between different types of motion in real-life examples?