Section 7 Looking at Lines

This topic is very important, and the skills learnt here you will use throughout your life.

Preparation for geometrical work

Here are some basic rules necessary for geometric construction work. Some of them are very obvious try to adopt good habits from the very beginning:

Activities for geometry and surveying

a. Making a set-square (90 degree angle)

b. Making a circle-maker

c. Making a square

d. Making an equilateral triangle

e. Constructing angles

f. Finding unknown lengths

g. Finding heights of trees
Hopefully you have gained confidence in your instrument (right-angled isosceles triangle), and can now move on to find the heights of various things such as trees, flagpoles, buildings, etc.

BC will equal AB (BC = AB - the height of the tree). But it is not quite as simple as that. The triangle has to be held at eye level and this height must be added on to length BC which will then be the same as the height of the tree. The vertical edge must be kept perpendicular to the ground. A plumb line may help.

h. Finding unknown length using a protractor
An unknown length can also be discovered by using a tape measure and a protractor. In the drawing below, line un is a wall of unknown length, and p is the protractor:

i. Finding heights using a clinometer (or inclinometer)
When trying to find the height of a vertical object such as a flagpole or tree, the method is to measure two angles and a side in order to make a scale drawing. You can make a clinometer like the one below:

left up right