Shapes you can pick up
You cannot pick up a square on paper. But you can pick up a dice. Things that have height, width and depth are called solids.
A cube (maths people also say it that way) has six same square faces. A dice, a Rubik’s cube.
A cuboid is a stretched cube: a shoe box, a brick, a book.
A sphere is perfectly round from every side. A ball, a globe.
A cylinder has two round ends and a curved side. A tin, a toilet-roll tube, a pot.
Look around the room. A toy box, a ball under the bed, a mug on the table, a sugar cube in the kitchen. All solids. All day you pick them up — and today you will start to call them by the right names. And you will learn to spot them even with your eyes shut, just by touch.
A shape from paper is flat. A solid is a thing. A flat shape has sides, a solid has faces, edges and corners. Today you will learn to tell them by touch and by eye.
Sofie ties a scarf over Filip’s eyes. “Guess what you are holding!” She hands him a tin. Filip feels: “Two flat round ends… curved sides… a cylinder! Is it a tin?” A point. Next thing: all flat faces, all the same, sharp edges. “A cube!” It is a dice from Ludo. Then a little ball — “a sphere, that’s easy.” At last a tea box: flat faces, but some longer. “A cuboid!” Filip guesses even without eyes. Solids can be spotted with hands. Then they swap. Sofie knows everything except a matchbox — a cuboid like a cube, who can tell. Filip hints: “Compare the faces!”
Does it roll every way? A sphere. Does it roll only on its side? A cylinder. Does it not roll at all and has flat faces? A cube or a cuboid.
How to spot a solid
A spotting method, even with your eyes shut:
1. Does it roll? Put the solid on the table and give it a push.
- It rolls any way → a sphere. It is round from every side.
- It rolls only one way (on its side) → a cylinder. Stood on its end it stands, laid down it rolls.
- It does not roll → it has flat faces, go to step 2.
2. Compare the faces.
- All six faces are the same squares → a cube.
- The faces are rectangles, some longer → a cuboid.
A solid dictionary: a face is a flat surface (a cube has 6 of them). An edge is the line where two faces meet (a cube has 12 of them). A corner (vertex) is the point where edges meet (a cube has 8 of them). A sphere has no face, no edge, no corner — that is why it rolls so nicely.
Why does it matter? 빌더s know it exactly: walls are built from cubes and cuboids, because they sit on each other. You cannot build a wall from spheres — they roll away. A cylinder is good for columns and tins. The shape of a solid says what it is good for.
Cube or cuboid? A shoe box
The box does not roll — all flat faces. Cube or cuboid?
I compare the faces: the lid is a big rectangle, the sides are smaller. The faces are not the same.
It is a cuboid.
A cube would have all six faces completely the same — all squares. A shoe box does not have that, it is long. A sugar-cube box is often a cuboid too. The name does not always tell the truth, the shape never lies.
Why does a tin roll only on its side?
I stand the tin on its end: it stands. The end is flat and even, it holds it.
I lay it on its side: it rolls. The sides are curved, the wrap has no flat surface.
That is the sign of a cylinder: two flat ends and a curved wrap.
A sphere always rolls — it has no flat surface to stand on. That is why you cannot keep a ball on a slope, but you can keep a tin standing.
Count the faces of a dice
I take a dice and turn it. I count the faces with dots.
Top one, bottom a second. Four around: front, back, left, right.
Together 6 faces. Each is a square and all are the same size.
That is why a dice always lands with exactly one number up — each face has the same chance. If the dice were a cuboid, the big faces would land more often. The game would be unfair.
Do not mix a flat shape and a solid: a square is drawn on paper, a cube is a thing in your hand. If you call a ball “a circle”, a maths person sits up. A ball is a sphere. A circle is its picture.
Practice: now you do it 🎲
Now try it for real. You will see all the questions at once, like on paper. 시작 with ten. If it goes well, add more.
Spot the solid: cube, cuboid, sphere, cylinder.
On paper
Paper, a pencil and a search trip around the flat.
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Find one cube at home, one cuboid, one sphere and one cylinder. Write what you found.
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Play guessing with your eyes shut with a parent: spot solids by touch and say how you knew.
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Try rolling: which of the solids you found rolls any way, which only on its side, which not at all?
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Count the faces of a box (a cuboid). There should be 6 of them.
Now you 💪
- I know a cube, a cuboid, a sphere and a cylinder — even by touch.
- I know what a face, an edge and a corner are.
- I can say what rolls and why.
Done when: You find all four solids at home and you spot them with your eyes covered.
What to take from this lesson
- Solids have height, width and depth. You pick them up.
- Cube: 6 same square faces. Cuboid: a stretched cube.
- A sphere rolls any way. A cylinder only on its side.
- A face is a surface, an edge is a line, a corner is a point.
- A ball is a sphere, not a circle. A circle is flat.
© 2026 Ing. Martin Polak / AlgoRhino · 콘텐츠 이용 약관