Week 1 – SS1 Second Term Technical Drawing Notes

SECOND TERM E-LEARNING NOTE
SUBJECT:TECHNICAL DRAWING
CLASS:SS1
TITLE:SECOND TERM SCHEME OF WORK

 

 Reference materials:
Technical drawing by J.N. Green.
Engineering drawing 1 by M.A.Parker and F.Pickup
Metal work technology by G.H. Thomas.
Drafting Technology and practice by William P. Spence
Technical Drawing by F.B Mayock( 1- 4 )
Basic technology for junior secondary schools book 1 by G.N Nneji, E.J. Okon, V.C. Nwachukwu, N.A. David, and T.C. Ogbuanya.Pages 1-17, 34-78.
Basic technology for junior secondary schools book 2 by I. Elekwa , O.A. Bamiro, A.O. Oluyide,
D.L Ladoye, A. Nurudeen and I.O. Akuru
Technical drawing for senior secondary schools by Y.A Thanni and C.A Faseun-Motesho Pages 97-103

 
 WEEK ONE DATE:………………
Revision of last term work. Inscribed and circumscribed circles
        
Content:
(i) Inscribed circles.
(ii) Circumscribed circles

 Inscribed circles
Example 1 To inscribe a circle in a given triangle.

 
 
 Method:
Draw the given triangle ABC.
Bisect any two angles whose bisectors intersect at point O.
Draw a line from point O perpendicular to any side of the triangle ie OD.
With the compass pin at point O and radius OD, draw the required circle.

 Example 1 To inscribe three equal circles in an equilateral triangle, each circle to touch two sides and
two other circles

 
 
 
 
 
 Method:
(i) Draw the given equilateral triangle.
(ii) Bisect any two of the angles e.g X and Y to obtain the centre of the triangle, O.
(iii) Draw a line from Z through O to B.
(iv) Bisect angle OBC to obtain the centre of one of the circles, A.
(v) With O as centre and radius OA, locate the centres 1 and 2 of the remaining two circles.
(vi) Drop a perpendicular from A which meets line XB at point C. AC is the radius of the three circles.
(vii) With compass pin at points A, 1 and 2 in turn, draw the three circles.

 Example 3To inscribe a circle in any sector.

 
 
 
 
 
 
 Method:
(i) Bisect the vertical angle R. This angular bisector meets the arc of the sector at point S.
(ii) Construct a tangent at point S.
(iii)Extend the radius of the sector to meet the tangent at points P and Q.
(iv)Bisect one of the base angles e.g< RQS to obtain the centre of the circle, O.
(v) With O as centre and radius OS, draw the required circle.
Example 4To inscribe a circle in any regular polygon, rhombus or deltoid(kite).

 
 
 
 Method:
(i) Bisect any two angles of the given polygon. The two bisectors meet at a point O.
(ii) Point O is the centre of the circle. Drop a perpendicular from O to any side of the polygon, ie OD.
(iii)With O as centre and radius OD, draw the required circle.

 Evaluation Questions
1. A triangle ABC stands on side AB as base and has the following dimensions: AB = 60mm, AC = 50mm
and angle CAB = 67⁰. Construct the triangle and draw a circle in it.
2. Construct a regular polygon whose side is of length 40mm. Draw a circle in it to touch all the sides.

 
 Circumcribedcircles

 Example 1 To circumscribe a circle on a triangle or inscribe a triangle in a circle

 
 
 
 
 Method:
(i) Draw the given triangle ABC.
(ii) Bisect any two sides of the triangle ie AC and BC, These bisectors intersect at point O.
(iii) With O as centre and radius OA or OB or OC, draw a circle to pass through the three points.

 Evaluation Questions

 1. Construct a triangle ABC on AB as base with AB = 70mm, AC = 57mm and BC = 76mm. Circumscribe a
circle on it.
2. Construct a triangle ABC with side AB = 70mm, AC = 90mm and < ABC = 105⁰. Circumscribe a circle
on it.

 General evaluation/revisionalquestions

 1. A triangle has a perimeter 130mm, base 40mm and a base angle 105⁰. (i) Construct the triangle.
(ii) Measure and state the other base angle. (WAEC)
2. Construct a triangle PQR with base = 70mm, vertical height = 50mm and vertical angle = 55⁰
(WAEC)
3. Construct a triangle whose perimeter is 120mm and of sides in the ratio 3:4:5. (WAEC).
4. Construct a triangle of sides AB = 60mm, AC = 55mm and < ABC = 60⁰. Construct a triangle similar
to this and whose perimeter is 140mm.
5. Inscribe an octagon in a square of side 80mm.

 Reading assignment
Technical drawing by JN Green.Pages 20-22.

 Weekend Assignment
Objective

 
 
 1. Which of the following best describe the figure shown above? A. Inscribed. B. Circumscribed.
C. Escribed. D. Rebated.

 
 
 
 
 
 2. The circle P in the figure above can best be described as A. inscribed. B. circumscribed. C. escribed.
D. concentric.
3. Which of the following is correct in inscribing a circle in a triangle? A. Bisect one of the angles.
B. Bisect two sides of the triangle. C. Bisect two angles. D. Bisect three sides.
4. In order to circumscribe a circle on a triangle, which of the following is a correct step? A. Bisect two
sides of the triangle. B. Bisect two angles of the triangle. C. Bisect one side and angle. D. Bisect two
angles and one side.
5. Which of the following represents the radius of the circle drawn below? A. QR. B. OT. C. OP.
D. OQ

 
 
 
 Theory
1. Construct a triangle PQR with side PQ = 80, and angle PQR = QPR = 60⁰. (show all construction lines).
(i) Find the lengths PR and QR. (ii) Inscribe a circle in the triangle PQR. (iii) Name the triangle PQR.
2. Construct a triangle ABC with side AB = 50mm, AC = 90mm and < ABC = 105⁰. Circumscribe a circle
on the triangle.