Scale Drawing and Bearing

Scale Drawing and Bearings

Introduction

Objectives

• Make and interprete scale drawings

• Calculate bearings

Scale drawings

• A drawing which has been reduced or enlarged from its original size, to a specified scale. 

• A scale drawing is used when measurements are needed and an object is too large or too small to draw its actual size.

• A scale drawing is used in which all the dimensions are reduced or enlarged by a scale factor.

• The scale allows you to convert the dimensions on the drawing into the dimensions in real life. The scale is given as a fraction or a ratio.

Finding Lengths

A scale can be shown as a ratio which compares the drawing or model to the real object.

Example 1

• If the distance on a map is enlarged by a scale factor of 50 000 to give the actual distance, the scale of the map would be written as...

• The scale = 1 : 50 000 or 1/50 000

• 
  

Example 2

• A map is drawn using a scale of 1 : 50 000.

  There is a distance of 5 cm between two points on the map. What is the actual distance this represents?

• 1 : 50 000 means that 1 cm on the map represents 50 000 cm in real life.

  Real length = 5 x 50 000 = 250 000 cm = 2.5 Km

Example 3

• A scale drawing of a microcip has a scale of 1 : 0.025.

  How big will the drawing be if the microchip is 1.4 mm long?

• Drawing length = real length / n

• Drawing length = 1.4 / 0.025 = 56 mm = 5.6 cm

Multiple Choice

A scale drawing of a mobile phone has a scale of 1 : 0.2.

Which of these statements is correct?

• The scale drawing and the mobile phone are the same size.

• The scale drawing is larger than the mobile phone.

• The mobile phone is larger than the scale drawing.

  Answer

Multiple Choice

A scale drawing has a scale of 1 : 100.

On the drawing, a length is 4 cm. How long is the actual length in centimetres?

• 400

• 40

• 0.4

• 0.04

Multiple Choice

A scale drawing is drawn with a scale of 1 : 1000.

On the drawing, a length is 5.6 cm. What is this actual length in centimetres?

• 56000

• 5600

• 560

• 0.56

Multiple Choice

A scale drawing has a scale of 1 : 100.

In real life, a length is 800 cm. How many centimetres will this be on the scale drawing?

• 0.08

• 0.8

• 8

• 80

Bearings

• An angle that is measured clockwise from north. 

• The angle is always shown using three digits and may also be called a three-figure bearing.

Relate Angles to Compass Points

• N = 000⁰

• NE = 045⁰

• E = 090⁰

• SE =135⁰

• S = 180⁰

• SW = 225⁰

• W = 270⁰, NW = 315⁰

Example 4

• The bearing of A from O is ...

• The bearing is an angle measured clockwise from north.

  It must always be written using three digits.

• Bearing = 043⁰

Example 5

• The bearing of B from O is ...

• Bearing = 090⁰ + 072⁰ = 162⁰

Multiple Choice

What is the bearing of NW?

• 045⁰

• 135⁰

• 225⁰

• 315⁰

Multiple Choice

What is the bearing of South?

• 090⁰

• 180⁰

• 225⁰

• 315⁰

Multiple Choice

The diagram shows the direction to Antville.

What is the bearing for this direction?

• 050⁰

• 180⁰

• 230⁰

• 300⁰

Multiple Choice

Calculate the bearing from O to C.

• 43⁰

• 043⁰

• 133⁰

• 143⁰

Multiple Choice

The compass bearing from the camping area (circled in red) to Bowall Visitors Centre (circled in red) is:

• NE

• SE

• NW

• SW

Multiple Choice

A boat left port and travelled on a bearing of 210°.

Which picture best represents the direction of the boat?

Multiple Choice

Two ships left port and travelled on bearings of 040° and 280°.

Calculate the obtuse angle between the two ships.

• 040⁰

• 120⁰

• 130⁰

• 280⁰

Exercise/Homework

1. From ixl.com, Algebra 1, C.7
2. Minimum score = 80
3. Deadline : Friday, 2 October 2020, 8 p.m.