Question 1:
Are the tape and rod similar to the scale that the elder sister has in her geometry box? What did mother mean by char angula?
Answer:
- Yes, the tape and the rod are similar to the scale in the geometry box because they are all used to measure length. The tape is flexible, the rod is rigid, and the scale is small and straight.
- Char angula means four finger widths. Deepa’s mother used her fingers to measure length. In olden times, people used body parts like fingers (called “angula”) to measure things.
Question 2:
Would it be convenient to use the unit metre to measure larger lengths, such as the length of a railway track between two cities, or to measure smaller lengths, such as the thickness of a page of a book?
Answer:
- No, it would not be convenient. For very large lengths like the distance between cities, we use kilometres. For very small lengths like the thickness of a page, we use millimetres.
Question 3:
Suppose we all measure the length of the table again, but this time using a metre scale. Will our results still be different?
Answer:
- Yes, the results might still be slightly different if we do not measure carefully. But using a standard metre scale will make our measurements more similar than using handspans.
Question 4:
Why are some length measuring devices made up of flexible materials?
Answer:
- Some measuring devices are flexible so we can measure curved or round objects easily. For example, a tailor’s tape can wrap around a person’s body to measure their waist.
Question 5:
What do such kilometre stones indicate? How could Padma conclude that she was getting closer to her destination?
Answer:
- Kilometre stones show the distance to a place from that point. As Padma saw the numbers on the stones decreasing, she knew she was getting closer to Delhi.
Question 6:
Does this mean that the position of Padma, with respect to the reference point, is changing with time? When does the position of an object change with respect to a reference point? Does it change when an object is moving?
Answer:
- Yes, Padma’s position relative to Delhi (the reference point) is changing with time.
- The position of an object changes with respect to a reference point when it moves.
- So, when an object is moving, its position changes.
Question 7:
How can one decide if an object is in motion or at rest?
Answer:
- An object is in motion if its position changes with time compared to a reference point.
- An object is at rest if its position does not change with time compared to the reference point.
Question 8:
Suppose you are travelling on a ship which is moving at a constant speed along a straight line on a calm sea. Suppose there is no window on the ship. Is there any way that you can determine whether the ship is moving or is stationary?
Answer:
- No, without looking outside or feeling any movement, you cannot tell if the ship is moving at a constant speed. It might feel like the ship is stationary.
Question 9:
Does it move along a straight line? When an orange drops from the tree, does it move in a straight line? Have you seen the Republic Day parade? Recall the march-past of students during the parade. Do they move on a straight-line path?
Answer:
- Yes, when we drop an eraser or an orange, it moves down in a straight line.
- In a parade, students march in a straight line path.
Question 10:
Is the motion of the eraser the same as that of a merry-go-round?
Answer:
- Yes, when we whirl an eraser tied to a string, it moves in a circular path, like a merry-go-round.
Question 11:
Does it start moving to and fro? Is its motion similar to the motion of a swing?
Answer:
- Yes, when we release the eraser hanging from a thread, it moves back and forth, like a swing.
Question 12:
Does it move up and down? This is also an example of oscillatory motion.
Answer:
- Yes, the free end of the metal strip moves up and down when released. This is an example of oscillatory motion.
Activity 5.1: Let us measure
Select some objects around you, such as a comb, a pen, a pencil, and an eraser to measure their lengths.
Measure their lengths one by one using a metre scale and note down the measurements in Table 5.2.
Answer:
| Object | Length of the object |
|---|---|
| Comb | 15 cm |
| Pen | 14 cm |
| Pencil | 10 cm |
| Eraser | 5 cm |
Activity 5.2: Let us explore
Look around and prepare a list of five objects that are in motion and five objects that are at rest.
Record your observations in Table 5.3.
Think about how you decided whether an object was in motion or at rest. Write your explanation (justification) in Table 5.3.
Answer:
Objects in motion
| Objects in Motion | Justification |
|---|---|
| Bird flying | It is moving in the sky |
| Car moving | It is changing position on the road |
| Dog running | It is moving from one place to another |
| Leaves falling | They are moving down from the tree |
| People walking | They are changing their positions while walking |
Objects at rest
| Objects at Rest | Justification |
|---|---|
| Tree | It is not moving |
| House | It stays in the same place |
| Parked bicycle | It is not moving |
| Bench | It does not change position |
| Sleeping cat | It is not moving (if not moving paws) |
Activity 5.3: Let us explore
Take an eraser and drop it from a certain height.
Observe its motion.
Answer:
- When I dropped the eraser, it moved downward in a straight line towards the ground. This is linear motion.
Activity 5.4: Let us investigate
Tie an eraser (or a potato) at one end of a thread.
Hold the other end of the thread with your hand and whirl it.
Observe its motion.
Is the motion of the eraser the same as that of a merry-go-round?
Answer:
- When I whirled the eraser, it moved in a circle around my hand.
- Yes, its motion is like a merry-go-round, which is circular motion.
Activity 5.5: Let us investigate
Tie an eraser (or a potato) at one end of a thread.
Hang the eraser by holding the other end of the thread. Keep your hand steady.
Using the other hand, take the eraser slightly to one side and then release.
Does it start moving to and fro? Is its motion similar to the motion of a swing?
Answer:
- Yes, when I released the eraser, it started moving back and forth.
- Its motion is similar to a swing, which is oscillatory motion.
Activity 5.6: Let us investigate
Take a thin metal strip of about 50 cm long.
Hold its one end pressed to a table. You may use a few books or a brick to hold it.
Press the free end of the strip slightly and let it go.
Observe the motion of this end of the strip.
Does it move up and down?
Answer:
- Yes, the free end of the strip moved up and down when I let it go.
- This is also an example of oscillatory motion.
Activity 5.7: Let us identify
Look at the picture of a children’s park or visit a children’s park.
Observe different kinds of motions. Classify them as linear, circular or oscillatory motion.
List them in Table 5.4. Give your justification for why you put each in a certain category.
Answer:
| Object | Linear motion | Circular motion | Oscillatory motion | Justification |
|---|---|---|---|---|
| Swing | Yes | Moves back and forth like a pendulum | ||
| Slide | Yes | Children move down in a straight line | ||
| Merry-go-round | Yes | Rotates in a circle | ||
| Seesaw | Yes | Moves up and down | ||
| Children running | Yes | Move in straight paths | ||
| Bicycle wheels | Yes | Wheels rotate in circular motion |
Question 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.
Answer:
| Column I | Column II (Unit) |
|---|---|
| Distance between Delhi and Lucknow | kilometre |
| Thickness of a coin | millimetre |
| Length of an eraser | centimetre |
| Length of school ground | metre |
Question 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
(ii) True
(iii) False (Correct: 1 km = 1000 m)
Question 3:
Which of the following is not a standard unit of measuring length?
(i) millimetre (ii) centimetre (iii) kilometre (iv) handspan
Answer:
- (iv) handspan is not a standard unit.
Question 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:
| Measuring Device | Smallest Value Measured |
|---|---|
| 15-cm ruler | 1 millimetre (1 mm) |
| Measuring tape | 1 millimetre (1 mm) |
| Metre scale | 1 millimetre (1 mm) |
| Tailor’s tape | 1 millimetre (1 mm) |
Question 5:
Suppose the distance between your school and home is 1.5 km. Express it in metres.
Answer:
- 1 km = 1000 metres
- 1.5 km = 1.5 × 1000 = 1500 metres
Question 6:
Take a tumbler or a bottle. Measure the length of the curved part of the base of glass or bottle and record it.
Answer:
- I measured the curved part (circumference) of the bottle’s base using a thread. It was 20 centimetres.
Question 7:
Measure the height of your friend and express it in (i) metres (ii) centimetres and (iii) millimetres.
Answer:
- My friend’s height is:(i) 1.3 metres(ii) 130 centimetres
(iii) 1300 millimetres
Question 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:
- Estimate:
- Length of notebook: 24 cm
- Diameter of coin: 2 cm
- Estimated number of coins: 24 cm ÷ 2 cm = 12 coins
- Verification:
- Measured length of notebook: 24 cm
- Measured diameter of coin: 2 cm
- Number of coins needed: 24 cm ÷ 2 cm = 12 coins
- So, 12 coins are required.
Question 9:
Give two examples each for linear, circular and oscillatory motion.
Answer:
- Linear Motion:
- A car moving on a straight road.
- A train moving along straight tracks.
- Circular Motion:
- The hands of a clock moving around.
- A child riding a merry-go-round.
- Oscillatory Motion:
- A swing moving back and forth.
- A pendulum of a clock.
Question 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:
| Size | Objects |
|---|---|
| mm | Thickness of a coin (2 mm) |
| Thickness of a notebook (5 mm) | |
| Width of a small key (10 mm) | |
| cm | Length of a pencil (15 cm) |
| Width of a book (20 cm) | |
| Height of a chair seat (45 cm) | |
| m | Height of a door (2 m) |
| Length of a car (4 m) | |
| Width of a room (5 m) |
Question 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.
Answer:
- From A to B: Linear motion (straight down)
- From B to C: Circular motion (loop)
- From C to D: Linear motion (straight up)
- From D to E: Oscillatory motion (if the ball swings)
- From E to F: Linear motion (straight exit)
Question 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?
Answer:
- She should not use cloth and stretchable rubber because they are flexible and can stretch, making measurements inaccurate.
- She can use plywood, paper, or steel as they are rigid.
Question 13:
Think, design and develop a card game on conversion of units of length to play with your friends.
Answer:
- I can create cards with lengths in different units (mm, cm, m, km).
- Players draw cards and have to convert the length to another unit.
- For example, convert 1500 mm to cm.
- Correct answers earn points. The player with the most points wins.
Question:
Can you find the thickness of a single page of your notebook or textbook using a scale? Think of a way and write it. Carry out the activity and report your result.
Answer:
- Yes, I can measure the thickness of 100 pages together.
- Suppose 100 pages measure 1 cm.
- Then, thickness of one page = 1 cm ÷ 100 = 0.01 cm or 0.1 mm.
Question:
Collect fallen leaves from the same tree. Identify the name of the tree whose leaves you have taken. Measure length and breadth of all these leaves using a 15-cm scale. Record your observations in the Table 5.7.
Discuss why the leaves of the same tree vary in length and breadth.
Answer:
| S. no. | Name of tree | Length of leaf (cm) | Breadth of leaf (cm) |
|---|---|---|---|
| 1 | Neem tree | 10 cm | 4 cm |
| 2 | Neem tree | 9 cm | 3.5 cm |
| 3 | Neem tree | 11 cm | 4.2 cm |
| 4 | Neem tree | 8.5 cm | 3 cm |
| 5 | Neem tree | 10.5 cm | 4 cm |
- Leaves vary in size due to factors like age of the leaf, amount of sunlight, and nutrition.