Class 6 Science · Chapter 5

5. Measurement of Length and Motion

Answers to in-text questions, activities and Let us enhance our learning. NCERT Curiosity, Class 6 Science (CBSE).

In-text Questions

Why is the number of handspans different for all the students when they measure the same table?

The handspans of different students are of different sizes. So the number of handspans is different.

Units like handspan, foot or fist differ from person to person. So we need standard units.

Would it be convenient to use the unit metre to measure larger lengths, like a railway track between two cities, or smaller lengths, like the thickness of a page?

No. For larger lengths we use kilometre. For smaller lengths we use centimetre or millimetre.

1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm

What are the points to take care of while measuring length?

Place the scale in contact with the object along its length.
Keep the eye directly above the point to be read.
If the end of the scale is broken, start from a full mark such as 1.0 cm. Subtract this reading from the reading at the other end.

5.1Measure the lengths of some objects using a scale (Table 5.2).

Object	Length
Comb	12.5 cm
Pen	14.2 cm
Pencil	17.5 cm
Eraser	4.0 cm

These are sample readings. Measure your own objects. Always write the number and the unit, with a space between them.

How would Anish and his parents have measured the length of string lights for the curved arches?

They could use a flexible measuring tape. Or they could place a thread along the curved arch, straighten it and measure it with a metre scale.

What do kilometre stones indicate? How could Padma conclude that she was getting closer to her destination?

Kilometre stones show the distance from a place. Here, Delhi is the reference point.

The distance on the stones kept decreasing — 70 km, then 60 km. So Padma knew she was getting closer to Delhi.

5.2List five objects in motion and five objects at rest with justification (Table 5.3).

Objects in motion	Objects at rest
Cow grazing in the field	Tree
Bus moving on the road	School building
Bird flying in the sky	Electric pole
Blades of a running fan	Parked car
Child running in the playground	Blackboard

Justification: Objects in motion change their position with respect to a reference point (like a building) with time. Objects at rest do not change their position.

Suppose you are on a ship moving at a constant speed along a straight line on a calm sea, with no window. Can you find whether the ship is moving or not?

No. Everything inside the ship stays at rest with respect to us. Without seeing anything outside, we cannot tell whether the ship is moving or stationary.

5.7Classify the motions seen in a children’s park as linear, circular or oscillatory (Table 5.4).

Object	Type of motion	Justification
Swing	Oscillatory	Moves to and fro
See-saw	Oscillatory	Moves up and down about a fixed point
Merry-go-round	Circular	Moves along a circular path
Giant wheel	Circular	Moves along a circular path
Child on a slide	Linear	Moves along a straight line
Child running straight	Linear	Moves along a straight line

Let us enhance our learning

1Match the lengths in Column I with the suitable units in Column II.

Column I	Column II
Distance between Delhi and Lucknow	kilometre
Thickness of a coin	millimetre
Length of an eraser	centimetre
Length of school ground	metre

2Mark True (T) or False (F).

(i) The motion of a car moving on a straight road is an example of linear motion. — True

(ii) Any object which is changing its position with respect to a reference point with time is said to be in motion. — True

(iii) 1 km = 100 cm — False. 1 km = 1000 m = 1,00,000 cm.

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

(iv) handspan — it differs from person to person.

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

Scale / tape	Smallest value
15-cm scale	1 mm
Metre scale	1 mm
Tailor’s tape	1 mm
Carpenter’s steel tape	1 mm

Look at your own scales carefully. Some old tapes may have 0.5 cm as the smallest division.

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

1 km = 1000 m

1.5 km = 1.5 × 1000 m = 1500 m

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

Wrap a thread once around the base of the tumbler. Mark the point where it meets. Straighten the thread and measure it with a scale.

Sample reading: Length of the curved base of the tumbler = 22.0 cm

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

Sample: Height of my friend = 145 cm

(i) 1.45 m (ii) 145 cm (iii) 1450 mm

1 m = 100 cm and 1 cm = 10 mm.

8Estimate how many coins placed lengthwise will cover the length of one side of a notebook. Verify using a 15-cm scale.

My estimate: about 10 coins.

Measurement: Length of the notebook side = 24.0 cm. Width of the coin = 2.3 cm.

Coins needed = 24.0 ÷ 2.3 = about 10 coins. So my estimate was correct.

Your values will depend on your notebook and coin.

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

Linear: a car on a straight road; an eraser falling from a height.
Circular: blades of a ceiling fan; a merry-go-round.
Oscillatory: a swing; the pendulum of a wall clock.

10List three objects each whose lengths are easier to express in mm, cm and m (Table 5.6).

Size	Objects
mm	Thickness of a coin, lead of a pencil, thickness of a notebook
cm	Eraser, pencil, textbook
m	Length of a classroom, height of a door, length of a saree

11A ball starts from point A on the rollercoaster track and escapes through point F. Identify the types of motion and the corresponding portions of the track.

A to B: Linear motion (straight track).
B to C to D to E: Circular motion (along the loop).
E to F: Linear motion (straight track).

12Tasneem wants to make a metre scale. She considers plywood, paper, cloth, stretchable rubber and steel. Which of these should she not use and why?

She should not use cloth and stretchable rubber. They stretch, so the length changes.

She should also avoid paper. It can fold or tear easily.

Plywood and steel are good. They are rigid and do not stretch.

13Think, design and develop a card game on conversion of units of length.

Make pairs of cards such as “1 km” and “1000 m”, “1 m” and “100 cm”, “5 cm” and “50 mm”, “2.5 km” and “2500 m”. Mix the cards face down. Each player turns two cards. If they are equal, the player keeps the pair. The player with the most pairs wins.

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