Lesson Notes By Weeks and Term v5 - Grade 3

Lesson Video

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Performance objectives

• Define and calculate perimeter.
• Define and find the area by counting squares.
• Understand the difference between perimeter and area.
• Understand and compare volume using words like 'holds more' or 'holds less'.

Lesson summary

This week, we dive into the practical world of Measurement.

We will explore three important concepts: perimeter, area, and volume. These are not just words in a maths book; they are ideas we use every day in our homes and communities in South Africa. When we help our family build a fence for a garden or a kraal, we are thinking about perimeter. When we lay down a new mat (like a beautiful grass icantsi mat) or help tile a kitchen floor, we are working with area. When we pour a glass of amasi or pack our lunchbox, we are judging volume. Understanding these concepts helps us solve real-life problems, plan projects, and make sense of the space around us.

Lesson notes

Perimeter: The Distance Around What is it? Perimeter is the total length of the border or boundary of a flat (2-D) shape. Imagine you are a little ant walking along the very edge of a shape; the total distance you walk is the perimeter. The word peri means 'around' and meter means 'measure'. So, it's the 'measure around'. How do we find it? To find the perimeter of any shape with straight sides (a polygon), we simply add the lengths of all the sides together. The unit of the perimeter will be the same as the unit of the sides (e.g., centimetres (cm), metres (m)).

Worked example

Nomsa has two lunchboxes. One is a small square box. The other is a big rectangular box. Which lunchbox has a larger volume?

Step 1: Look at the two objects. Visualize them in your mind or look at a picture.

Step 2: Think about how much they can hold. The big rectangular box can fit a bigger sandwich, an apple, and a juice box. The small square box can only fit a small sandwich.

Step 3: Compare using the correct language. The big rectangular box holds more food.

Therefore, it has a larger volume.

Guided Practice (With Solutions)

Question 1:

Find the perimeter and area of the shape below on the grid. Each side of a small square is 1 cm long.

```

+--+--+--+--+--+

|1 |2 |3 |4 |5 |

+--+--+--+--+--+

|6 |7 |8 |9 |10|

+--+--+--+--+--+

```

Solution 1:

Perimeter:

Method: We need to find the distance around the shape. The top side is 5 cm long. The right side is 2 cm long. The bottom side is 5 cm long. The left side is 2 cm long.

Calculation: Perimeter = 5 cm + 2 cm + 5 cm + 2 cm = 14 cm.

Answer: The perimeter is 14 cm.

Area:

Method: We need to count the number of squares inside the shape.

Calculation: We can count them one by one: 1, 2, 3, 4, 5, 6, 7, 8, 9,

1

0. Answer: The area is 10 square units (or 10 square cm).

Commentary: Notice how perimeter is a length (cm) and area is a measure of the surface (square cm). They measure different things!