# Length

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## 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 $\frac{1}{2}$ cm

Complete the table:

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

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