How Things Work
Class 4 · The World Around Us
4 ideas in Class 4 The World Around Us, explained in plain words, with games and quizzes to practise.
Spinning Motion and Centre Balance
Part of: Mechanics and Everyday Science
When an object like a coin, top (lattu), or cardboard disc spins around a central point, it stays upright as long as it has speed and symmetrical balance. As friction slows it down, it begins to wobble and fall.
Why it matters. Investigating spinning tops introduces children to balance, rotational symmetry, and the forces that govern rotating machines like fans and wheels.
Try it in two minutes
- Make a quick cardboard spinner using a circular disc and a toothpick poked right through the middle.
- Spin it and watch it stay upright; then poke the toothpick off-centre to see it wobble and topple.
- Discuss what happens to the apparent shape of a square card when spun rapidly.
Try at home. Colour four segments of a cardboard circular spinner with different bright colours and spin it fast to observe color blending.
Floating, Sinking, and Material Density
Part of: Mechanics and Everyday Science
Whether an object floats or sinks in water depends on its material and how much water it pushes aside. Light materials like dry wood and leaves float, while dense objects like iron nails and pebbles sink.
Why it matters. Learning about floating and sinking helps children understand basic physical properties of matter and observe that size alone does not determine buoyancy.
Try it in two minutes
- Drop a small dry leaf and a tiny iron nail into a bowl of water.
- Notice that the tiny nail sinks instantly while the larger leaf floats.
- Ask your child why a big empty plastic bottle floats while a heavy stone sinks.
Try at home. Test five small household objects (a coin, an eraser, a pencil, a cork, and a plastic spoon) in a bucket of water.
The Effect of Shape on Buoyancy
Part of: Mechanics and Everyday Science
An object's shape determines how much water it pushes aside. A sheet of aluminium foil floats when spread flat or shaped like a cup, but sinks when crushed tightly into a solid ball.
Why it matters. Discovering that shape affects buoyancy explains why heavy metal ships can float on water while solid metal balls sink.
Try it in two minutes
- Take a small square piece of aluminium foil and float it flat on water in a bowl.
- Shape another identical foil piece into a small cup and float it.
- Crumple the foil into a very tight, hard ball and drop it into the water to watch it sink.
Try at home. Take a lump of modelling clay: roll it into a ball (it sinks) and then flatten it into a wide boat bowl (it floats!).
Designing Stable Boats and Scientific Inquiry
Part of: Mechanics and Everyday Science
Boats can be made from folded paper, half coconut shells, walnut shells, or ice-cream sticks. A wide flat base keeps a boat balanced and stops it from flipping over in water.
Why it matters. Building toy boats encourages hands-on experimentation with balance, waterproofing, and structural stability, teaching engineering basics to young learners.
Try it in two minutes
- Fold a simple paper boat with your child and float it in a tub.
- Gently tap one side of the boat to see how well it balances without tipping.
- Try floating a half coconut shell or walnut shell and notice its natural boat-like shape.
Try at home. Float a half walnut shell with a tiny paper sail attached with a dab of dough and blow gently across the water.
What your child will practise
- Designing Stable Boats and Scientific Inquiry: Candy Quick Fire (Quick Fire)
- Designing Stable Boats and Scientific Inquiry: Lab Explorer Quest (Collect the Answer)
- Floating, Sinking, and Material Density: Ocean Sort (Sort It Out)
- Spinning Motion and Centre Balance: Space Quick Fire (Quick Fire)
- The Effect of Shape on Buoyancy: Ocean Puzzle (Clue Puzzle)
- Quiz: Designing Stable Boats and Scientific Inquiry (8 questions)
- Quiz: Floating, Sinking, and Material Density (8 questions)
- Quiz: Spinning Motion and Centre Balance (8 questions)
- Quiz: The Effect of Shape on Buoyancy (8 questions)