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# Length

Module by: Siyavula Uploaders. E-mail the author

## LENGTH

In this learning unit we shall be looking at different units used to measure length, as well as at the importance of measuring accurately.

### Activity 1:

• To measure and record [LO 4.5.3]
• To measure accurately with the appropriate measuring instruments [LO 4.7.3]

1. Let us start right away! How well do you know yourself? Measure the following as accurately as possible (your friend may help you):

1.1 the length of your thumb nail

1.2 the length of your little finger

1.3 the length of your right foot

1.4 the length of your left arm from your shoulder to the tip of your middle finger

1.5 How tall are you?

1.6 How high can you reach when you jump up from the ground?

1.7 How much higher is this than your height?

2. What did you use to measure the above?

3. What other measuring apparatus could we also use to measure length?

Do you still remember?

1 cm = 10 mm

1 m = 100 cm

1 m = 1 000 mm

1 km = 1 000 m

Did you know?

• One metre is roughly the distance from an adult’s nose to the tip of his middle finger on his stretched out hand.
• The length of a fingernail is roughly 1 cm.
• The length of a hand is roughly 10 cm.
• The space underneath your fingernail is roughly 1 mm.
• The breadth of a little finger is roughly 10 mm.

4. Work together with a friend and complete the following table.

 Measure Estimate Actual Measurement Difference a) the height of your educator ...................... ....................... ....................... b) the breadth of your classroom ...................... ....................... ....................... c) the height of your desk/table ...................... ....................... ....................... d) the total length of the blackboard in the classroom ...................... ....................... .......................

### To solve problems that include selecting, calculating with and converting standard units [LO 4.6]

1. It is important for us to know which measuring units are used for specific lengths. In order to do that correctly, we must know exactly how long the different measuring units are. Let us see how good you are at this! Choose a suitable unit to measure the following:

1.1 The chest size of Dad’s suit (of clothes) is 102 ____

1.2 The height of my bedroom wall is 4 ____

1.3 The breadth of the stoep of the farmhouse is 2,5 ______

1.4 The thickness of my dictionary is 40 _____

1.5 The distance between Johannesburg and Cape Town is more than 1 000 _____

1.6 The depth of the water in our swimming pool is 1,500 _____

2. Circle the measurement that is the closest to reality:

2.1 Our classroom door is about ____high.

(a) 20 m

(b) 200 mm

(c) 2 km

(d) 2 m

2.2 My foot is about ____long.

(a) 26 cm

(b) 26 mm

(c) 26 km

(d) 26 m

2.3 The distance from Durban to East London is ____

(a) 674 mm

(b) 674 km

(c) 674 m

(d) 674 cm

3. Let us look at the way of writing length in the decimal form:

We already know that 10 mm = 1 cm

Thus: 25 mm = 10 + 10 + 5 mm= 1cm + 1 cm + 5 mm= 2 cm + 5 mm= 2,5 cm of 2 1212 size 12{ { { size 8{1} } over { size 8{2} } } } {} cm

Complete the table:

 Number of mm 10 85 ............ 245 ............ 1 026 ............ Number of cm 1 ............ 4,2 ............ 17,9 ............ 146,3

4. We know that there are 1 000 mm in 1 m

Thus: 2 347 mm = 2 m 347 mm= 2,347 m

Complete the table:

 mm m e.g. 4 328 4,328 ..................... 3 367 ..................... ..................... 4,7 28 ..................... ..................... 0,067 6 .....................

5. In the same way 1 000 m = 1 km

Thus: 1 407 m = 1 km 407 m= 1,407 km

Complete the table:

 Distance in m 2 368 ............ 426 ............ 38 ............ 9 Distance in km 2,368 7 ............ 0,6 ............ 1,48 ............

### Activity 3:

• To measure two-dimensional figures [LO 4.5.3]

### SCALE:

DID YOU KNOW?

When we draw something, e.g. a house, we don’t draw it as big as it actually is.

We draw it to scale. The shape stays the same but the size is different (smaller). The knife below is drawn on a scale of 1:4

Now think about maps. Normally a place will be drawn much smaller than it actually is in reality. A scale tells us how to measure distances on a map. In the map below 1 cm equals 500 km.

1.1 What is the actual length of the knife above? 1_____

1.2

1. a) What is the actual distance, according to the scale, from town

A to town B?....................

1. a) And from C to D?....................

2. Determine the scale of each item below:

2.1 The actual length of the crayon is 15 cm.

Scale: .........................................

2.2 The actual length of the bottle is 80 cm.

Scale: .........................................

2.3 The actual length of the fish is 45 cm.

Scale: .........................................

• Now measure the distance. _____ mm
• How many cm is it?
• How many m is it?

Now take any 340 mℓ cool drink tin and measure the distance around it in mm.

## Assessment

 LO 4 MeasurementThe learner will be able to use appropriate measuring units, instruments and formulae in a variety of contexts. We know this when the learner: 4.1 reads, tells and writes analogue, digital and 24-hour time to at least the nearest minute and second; 4.2 solves problems involving calculation and conversion between appropriate time units including decades, centuries and millennia; 4.3 uses time-measuring instruments to appropriate levels of precision including watches and stopwatches; 4.4 describes and illustrates ways of representing time in different cultures throughout history; 4.5 estimates, measures, records, compares and orders two-dimensional shapes and three-dimensional objects using S.I. units with appropriate precision for:mass using grams (g) en kilograms (kg); capacity using millimetres (mm), centimetres (cm), metres (m) en kilometres (km); length using. millimetres (mm), centimetres (cm), metres (m) en kilometres (km); 4.6 solves problems involving selecting, calculating with and converting between appropriate S.I. units listed above, integrating appropriate contexts for Technology and Natural Sciences; 4.7 uses appropriate measuring instruments (with understanding of their limitations) to appropriate levels of precision including:bathroom scales, kitchen scales and balances to measure mass; measuring jugs to measure capacity; rulers, metre sticks, tape measures and trundle wheels to measure length.

## Memorandum

ACTIVITY 1

3. tape measure / metre stick / trundle / ruler / string / wool

Activity 2

1. 1.1: cm

1.2: m

1.3: m

1.4: mm

1.5: km

1.6: m

2. 2.1: 2 m

2.2: 26 cm

2.3: 674 km

3.

 42 179 1463 8,5 24,5 102,6

4.

 mm m 3 000 0,367 4 700 0,028 67 0,006

5.

 7 000 600 1 480 0,426 0,038 0,009

ACTIVITY 3

1. 20 cm

1.1: 1 250 km

1.2: 1 500 km

2. 2.1: 1:5

2.2: 1:20

2.3: 1:15

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