Chapter 7: How Things Work

Chapter at a Glance

Meera and Dhruv love to find out how things work. One Sunday, Meera spins a coin and notices that it shakes as it slows down. They try spinning a bangle, a pencil, a stone, a wooden top and an eraser, and find that round objects like coins and bangles spin well while erasers do not. They then make spinners from cardboard and toothpicks. A spinner with the toothpick exactly at the centre spins upright, but one with the toothpick away from the centre wobbles and falls. A square spinner looks round while spinning, and colours painted on a spinner seem to mix when it spins fast.

The chapter mentions many spinning things: ceiling fans, potter’s wheels, the charkha that Mahatma Gandhi used to spin cotton thread, and the lattu, a wooden top played with in India for thousands of years. After the rain, Meera and Dhruv make paper boats. Some boats float well while others flip over.

They then test which objects float or sink in a bucket of water. A leaf floats and an iron nail sinks, but an empty steel bowl floats even though it is heavy, while a small stone sinks. An empty closed bottle floats, but a bottle full of water sinks. Aluminium foil floats when spread out or shaped like a cup, but sinks when pressed into a tight ball. So floating and sinking depend not only on weight but also on shape and other factors. Finally, students make their own boats from ice-cream sticks, coconut shells or walnut shells and compare them.

Word Meanings

Important Topics

1. Objects that Spin

• Round objects that are the same on all sides spin well.

2. Making Spinners

• A spinner balances best when the hole is at the exact centre.
• Changing the toothpick length or card position can help it spin better.

3. Spinning Things Around Us

• Ceiling fan, potter’s wheel, charkha, lattu, merry-go-round, wheels of vehicles.
• Charkha: turns cotton fibre into thread; used by Mahatma Gandhi.
• Lattu: a popular Indian wooden top; early tops were made of clay.

4. Floating and Sinking

• Floating does not depend only on being light or heavy.
• Shape and the air inside also matter.

5. Shape Matters

• By changing the shape, we can make an object float or sink.

6. Making Boats

• Boats can be made from paper, cardboard, ice-cream sticks, clay, coconut shells or walnut shells.
• A good boat is strong, balanced and does not tip over.

Question-Answers

Very Short Answer Questions

1. What did Meera spin first? A coin.
2. What happens to a coin as it slows down? It begins to shake.
3. Name two objects that spin well. A coin and a bangle.
4. Name one object that does not spin properly. An eraser.
5. Where should the toothpick be for a spinner to spin well? At the exact centre.
6. How does a square spinner look while spinning? Circular.
7. What is a charkha used for? To twist cotton into thread.
8. What is a lattu? A popular Indian wooden spinning top.
9. Does an iron nail float or sink? It sinks.
10. Does an empty steel bowl float or sink? It floats.
11. What happens to foil pressed into a tight ball? It sinks.
12. What did Meera and Dhruv make after the rain? Paper boats.

Short Answer Questions

Q1. Why does a spinner with the hole at the centre spin better?

When the hole is at the centre, the spinner is the same on all sides, so its weight is balanced. It stays upright and spins smoothly.

Q2. What happens when a spinner with different colours spins fast?

The colours seem to mix together. We may see rings or a new colour instead of separate colours.

Q3. Why does an empty bottle float but a bottle full of water sink?

An empty closed bottle is full of air, which makes it float. When it is filled with water, there is no air inside, so it becomes heavy and sinks.

Q4. Why does an empty steel bowl float even though it is heavy?

Its bowl shape spreads over a large area of water and holds air inside, which keeps it on the surface.

Q5. Name some things around us that spin.

Ceiling fans, potter’s wheels, charkhas, spinning tops, bicycle wheels and merry-go-rounds.

Long Answer Questions

Q1. “Floating and sinking do not depend only on weight.” Explain with examples.

A light leaf floats and a heavy iron nail sinks, which seems to follow weight. But a heavy steel bowl floats, while a small stone sinks. An empty bottle floats, but the same bottle full of water sinks. Aluminium foil floats when flat or cup-shaped but sinks when pressed into a ball. So shape and the air inside an object also decide whether it floats or sinks.

Q2. Describe the activity with aluminium foil and what it shows.

Take three equal pieces of aluminium foil. Spread one out flat, shape one like a cup, and press one tightly into a ball. Put them in water. The flat and cup-shaped pieces float, but the tight ball sinks. This shows that the same material can float or sink depending on its shape.

Q3. How would you make a good boat? What should you keep in mind?

Collect materials like paper, cardboard, ice-cream sticks, clay and tape. Draw a design first, then build the boat with a wide, flat base so that it balances. Make it strong so that it does not break, and seal gaps so that water does not enter. Test it in water, see if it tips over, and improve the design.

Textbook Exercise Answers

Q1. Two questions Ravi could ask about his spinner.

(a) Why does the spinner slow down and stop on its own?

(b) What can I change so that my spinner spins for a longer time?

Q2. Figure it out.

(a) The figure is bending towards side A because that side is heavier. To balance it, add a little weight on side B, or move the support point slightly towards A, so that both sides weigh the same.

(b) To make a floating object sink, fill it with water or press it into a tight shape (like foil into a ball). To make a sinking object float, change its shape into a bowl or boat, or attach it to something light that floats, like cork or an empty bottle.

Q3. Float or sink.

Other in-text questions

• Which spinners did not spin properly, and why? The one with the toothpick away from the centre, because its weight was not balanced.
• Heavy objects that floated: empty steel bowl, empty bottle. Light objects that sank: a small stone, a coin, a tight foil ball.