Lesson Notes By Weeks and Term - Junior Secondary 3

TERM – 3^RD TERM

WEEK ELEVEN

Class: Junior Secondary School 3

Age: 14 years

Duration: 40 minutes of 5 periods each

Date:

Subject: BASIC TECHNOLOGY

Topic: SCALE AND SCALE DRAWING

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Define scale and scale drawing
2. Identify the types of scale drawing
3. Carryout simple scale drawings

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,

demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures, mathematical sets, drawing instruments

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

NOTE

SCALE AND SCALE DRAWING

A scale drawing is an enlargement of an object. An enlargement changes the size of an object by multiplying each of the lengths by a scale factor to make it larger or smaller. The scale of a drawing is usually stated as a ratio.

The scale represents the rate of enlargement or reduction from the original object.

Types of scale

1. Full Scale Drawing: A full scale drawing is a representation where the size of the objects is identical to their actual size in the real world. It's provides a direct and one-to-one correspondence between the drawing and the physical object, making it suitable for accurate measurements and detailed representations.
2. Reduction Scale Drawing: A reduction scale drawing depicts objects smaller than their actual size. It is commonly used when a large object or space needs to be represented on a smaller piece of paper, reducing the drawing to a manageable scale while maintaining proportional relationships.
3. Enlarged Scale Drawing: An enlarged scale drawing illustrates objects larger than their actual size. It is useful when intricate details or small components of an object need emphasis or when precision in design or construction requires a more magnified view.

Scaled Drawing

Scale: The scale is the relation between the actual measurements of an object and the measurements of a drawn object. For example, if a rectangular garden is drawn on a blueprint with a scale of 1 unit = 1 foot, that means every 1 unit of the drawing represents 1 foot of the garden in real life.

Procedure for Scale Drawing

1. Find the actual measurements of the drawing in the first given scale by multiplying. For example, if a side of a square is 6 units, and the scale is 1 unit = 2 cm, then the actual length of the side of the square is

   6 units x  2/1 = 12 cm

2. Find the new scale measurements by multiplying the actual measurements by the new scale. Keeping with the same example from Step 1, if the new scale is 1 unit = 3cm, then the new side measurement is

 12 cm x 1/3 = 4 units

3. Draw a new scaled drawing using the new scaled measurements, keeping the angle measurements the same.

Example: The drawing below has a scale of 1 unit = 10 ft. Reproduce the drawing with a scale of 1 unit = 5 ft.

Solution.

Procedure

1. Find the actual measurements of the height and the base:

Side AB: 5 units x 10/1 ft = 50 ft

Side AC: 12 units x 10/1 ft = 120 ft

2. Find the new scale measurements of the length and the width: by multiplying the actual measurements by the new scale.

Side A'B':

 50 ft x  1unit/ 12cm = 10 units

Side A'C':

 120 ft x 1 unit/12 cm = 24 units

3.Then, draw a new scaled drawing using the new scaled measurements.

Triangle A

EVALUATION: 1. The drawing below has a scale of 1 unit = 2 cm. Reproduce the drawing with a scale of 1 unit = 6 cm.

Rectangle ABCD. Side AD is 6 units and side DC is 9 units.

2. What is scale drawing?
3. Mention and explain the types of scale drawing.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively