Chapter 7 — How Things Work

Chapter 7 of the Class 4 The World Around Us NCERT textbook (Our Wondrous World), "How Things Work", introduces students to the science of spinning, floating, and sinking through hands-on activities with everyday objects like coins, bangles, tops, aluminium foil, and paper boats. Students observe how shape and weight affect whether things spin or stay balanced and whether objects float or sink in water. Download the PDF and read the chapter summary and Q&A below.

• Spinning — Tops, Coins, and Spinners — Students spin everyday objects — coins, bangles, pencils, stones, and wooden tops — and observe that not all objects spin equally well. They then make their own cardboard spinners using toothpicks and discover that placing the pivot at the centre helps the spinner stay upright and spin longer. Changing the position of the hole, the shape of the card (square vs circular), or adding colour patterns all affect how the spinner behaves.
• Floating and Sinking — Weight, Shape, and Material — Children test objects like a leaf, an iron nail, an empty steel bowl, a plastic bottle, and a piece of stone to predict and observe whether each floats or sinks. The chapter shows that floating or sinking depends not only on weight but also on shape and other factors. For example, an empty bowl floats while an iron nail of similar size sinks.
• Aluminium Foil Experiment — Shape Changes Everything — A key activity uses aluminium foil in three forms: spread flat, pressed tightly into a ball, and folded into a cup shape. When spread out or shaped like a cup the foil floats; when pressed into a tight ball it sinks. This demonstrates that the same material can float or sink depending purely on its shape.
• Designing and Testing Boats — Students design their own boats using materials like paper, cardboard boxes, ice-cream sticks, clay, and coconut or walnut shells. Groups compare the strength, balance, and stability of their designs in a class exhibition. The activity encourages creative engineering — some boats keep good balance while others tip over — and students reflect on how to improve their designs.

1. 01Students spin coins, bangles, pencils, erasers, and wooden tops to observe which objects spin and which do not.
2. 02Homemade cardboard spinners show that a toothpick placed at the centre makes the spinner spin better than one placed off-centre.
3. 03A square card spun fast appears circular, showing that shape seems to change when an object spins quickly.
4. 04Mahatma Gandhi used a charkha (spinning wheel) to spin cotton fibre into thread.
5. 05Spinning tops have been used in India for thousands of years; the lattu is a popular Indian top traditionally made of wood.
6. 06Floating or sinking depends on both weight and shape — not on weight alone.
7. 07Aluminium foil floats when spread flat or shaped like a cup, but sinks when pressed into a tight ball.
8. 08Students build boats from ice-cream sticks, coconut shells, walnut shells, and other everyday materials and compare designs in a class exhibition.