79
Flat surfaces. The plane
Textbook: Part 3, lesson 74, pp. 6–7
GoalThe idea of a flat surface and a plane; telling flat and curved surfaces apart.
New words
flat surface · yassi sirtplane · tekisliksolid body · hajmli jismcurved surface · egri sirt
Explanation
A flat surface is not bent: a table top, a board, a page. A plane is a flat surface that goes on forever in all directions. In drawings we usually show it as a sheet of paper. Solid bodies can have flat faces (a cube) or a curved surface (a ball).
Worked examples
A cube has 6 faces, all flat. The surface of a ball is curved.
We can cover a flat surface with triangles: no gaps are left between them.
Class activity
“Flat or curved?”: the teacher points to classroom objects (board, ball, notebook, the side of a glass). Children lay a hand flat on the desk for a flat surface, or make a round motion for a curved one.
Practice
1
How many flat faces does a cube have?
6
2
Is the surface of a ball a flat surface?
No, it is a curved surface
3
A flat surface is covered with triangles: 4 rows with 5 triangles in each. How many triangles in total?
20
4
A picture is 3 dm 5 cm long and 1 dm shorter in width. How many cm of frame strip (the perimeter) are needed?
120
5
1 m = 100 cm. Is a 1 m strip enough for this frame?
No: 120 cm > 100 cm