27
Practical lesson
Textbook: pp. 68–69
GoalApply geometry to practical tasks.
New words
foundation plan · poydevor tarxiset square · go‘niyapeg · qoziqrigidity · mustahkamlik
Explanation
For the practical work of marking a building’s foundation we need pegs, string, a tape measure and a large set square. One peg is driven in, string is pulled along the long wall and a second peg is placed at the measured distance. A set square gives a 90° angle for the third and fourth pegs, so the rectangle has right angles. If the foundation is 0.5 m thick, the inner sides are 1 m shorter than the outer sides. In the second task the rigidity of a triangle is tested. Only adults drive pegs and do building work; children take part in measuring and in the drawing.
Worked examples
A building 8 m × 5 m on the outside with a foundation 0.5 m thick has inside dimensions 7 m × 4 m.
Outer perimeter 2 · (8 + 5) = 26 m, inner perimeter 2 · (7 + 4) = 22 m.
Class activity
“Marking a plot”: in the school yard (with an adult), mark a 6 m × 4 m rectangle with sticks and string and check the corners with a large set square.
Practice
1
Outer size 10 m × 6 m, wall thickness 0.5 m. Find the outer perimeter (m).
32
2
Inner perimeter of the same building (inner size 9 m × 5 m) in metres?
28
3
How can you check with pegs that the corners of the marked quadrilateral are right angles?
By fitting a set square into the corner and checking that both sides lie along it.
4
Why is the inner perimeter of a foundation shorter than the outer one?
Each inner side is shorter by twice the wall thickness (2 · 0.5 = 1 m); with four sides the inner perimeter is 4 m less.