17
Practical lesson
Textbook: pp. 42–43
GoalPractise measuring heights, angles and drawing perpendiculars.
New words
height · balandlikset square · go‘niyaangle of a staircase · zinapoya burchagiprotractor · transportir
Explanation
By the height of an object we mean the length of the perpendicular segment from its top point down to the flat surface it stands on. A perpendicular line can be drawn with a protractor or a set square. With a protractor, to lay an angle on a ray, place its base on the ray and centre at the vertex, then mark the needed division; one such angle can be laid in each half-plane of the ray. A comfortable staircase angle is about 30°–45°; a very steep stair is dangerous. Measure heights only of low objects and with adults; do not climb up high.
Worked examples
A 50° angle can be laid in either half-plane of the ray: one in each, two in all.
A staircase 1.2 m high that rises at 40° lies in the comfortable range (30°–45°).
Class activity
“Measure the height”: measure the height of a desk, box and book with a ruler; check with a set square that the ruler is perpendicular to the base.
Practice
1
In how many ways can a 70° angle be laid on a given ray (two half-planes)?
2
2
A staircase has angle 38°. Is that within the comfortable range (30°–45°)?
Yes
3
Perpendiculars are drawn to d at three points A, B, C. How are they placed relative to each other?
They never intersect (all perpendicular to one line).
4
Why is height measured along a perpendicular?
The perpendicular gives the shortest distance; an oblique line would be longer.