Lesson Notes By Weeks and Term v5 - Grade 3
Measurement: perimeter, area (counting squares) and volume (intro) – Week 4 focus
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Measurement: perimeter, area (counting squares) and volume (intro) – Week 4 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Mathematics
Class: Grade 3
Term: 3rd Term
Week: 4
Theme: General lesson support
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Welcome, Grade 3 learners! This week, we're going on a mathematical adventure into the world of measurement! We'll be exploring perimeter, area, and get a sneak peek at volume. Measurement is all about figuring out how big things are – how long, how much space they cover, and how much they can hold. Imagine helping your family build a fence around your garden or figuring out how much space your blanket covers on your bed - that’s measurement in action! In South Africa, measurement skills are essential for everything from building houses and roads to cooking delicious meals and making sure we have enough water in our dams.
Perimeter: The perimeter is the distance around a shape. Think of it like walking around the edge of your school's playground – the total distance you walk is the perimeter! To find the perimeter, we add up the lengths of all the sides of the shape. The units we use for perimeter are the same as the units we use for length, like centimetres (cm) or metres (m).
Example 1: A square has sides of 5 cm each. What is its perimeter?
Explanation:* A square has 4 equal sides. To find the perimeter, we add the length of each side: 5 cm + 5 cm + 5 cm + 5 cm.
Calculation:* Perimeter = 5 cm + 5 cm + 5 cm + 5 cm = 20 cm Answer:* The perimeter of the square is 20 cm.
Example 2: A rectangle has a length of 8 cm and a width of 3 cm. What is its perimeter?
Explanation:* A rectangle has two pairs of equal sides. The length is 8 cm and there are two sides with that length. The width is 3 cm and there are two sides with that width.
Calculation:* Perimeter = 8 cm + 8 cm + 3 cm + 3 cm = 22 cm Answer:* The perimeter of the rectangle is 22 cm.
Area: The area is the amount of space a shape covers. Imagine painting the floor of your classroom. The area is how much floor you paint. We measure area in square units, because we are covering a 2-dimensional space. We use square centimetres (cm²) or square metres (m²) to measure area. We will find the area by counting squares that cover the shape.
Example 3: A rectangle is drawn on a grid, and it covers 12 small squares. Each square is 1 cm x 1 cm (1 cm²). What is the area of the rectangle?
Explanation:* We are told that each square is 1 square cm. So to find the area, we count the number of squares.
Calculation:* Area = 12 squares x 1 cm²/square = 12 cm² Answer:* The area of the rectangle is 12 cm².
Example 4: A square has sides of 3 cm each. We draw the square on a grid made of 1 cm squares. How many squares will the square cover?
Explanation:* Since we are drawing a 3 cm x 3 cm square on a grid of 1 cm squares, we need to work out how many 1 cm squares fit inside.
Visualisation:* Imagine drawing the square. It would have 3 rows of 3 squares, giving us 9 squares in total.
Calculation:* Area = 9 squares x 1 cm²/square = 9 cm² Answer:* The area of the square is 9 cm².
Volume (Introduction): Volume is the amount of space an object takes up. It's how much stuff is inside something. Think of filling a bottle with water – the volume is the amount of water the bottle can hold. We can compare the volume of different objects by filling them with something like blocks or marbles and counting how many fit inside. We will just focus on comparing the volume of objects using informal units this week. Next year, you will learn to measure volume properly!
Example 5: You have two boxes. Box A is filled with 10 blocks. Box B is filled with 15 blocks. Which box has a larger volume?
Explanation:* We are using blocks to measure volume. The box that holds more blocks has a larger volume.
Answer:* Box B has a larger volume because it can hold 15 blocks, which is more than Box A which can only hold 10 blocks. Guided Practice (With Solutions)
Question 1: A rectangular garden has a length of 6 m and a width of 4 m. What is the perimeter of the garden?
Solution:* Perimeter = 6 m + 6 m + 4 m + 4 m = 20 m Answer:* The perimeter of the garden is 20 m.
Commentary: Remember to add up all the sides of the rectangle. A common mistake is to only add the length and width, and forget to double them.
Question 2: A square has a perimeter of 24 cm. How long is each side of the square?
Solution:* A square has 4 equal sides. So, we need to divide the total perimeter by 4 to find the length of one side. Side length = 24 cm / 4 = 6 cm Answer:* Each side of the square is 6 cm long.
Commentary:* This question works in reverse. Understanding the definition of perimeter (sum of all sides) is crucial here.
Question 3: A rectangle is drawn on a grid. It is 5 squares long and 2 squares wide. Each square is 1 cm². What is the area of the rectangle?
Solution:* We can count the squares, or we can think of it as 5 rows of 2 squares. Area = 5 squares/row 2 rows = 10 squares Area = 10 squares 1 cm²/square = 10 cm² Answer:* The area of the rectangle is 10 cm².
Commentary:* Drawing the rectangle on a piece of paper helps with visualization.
Question 4: You have a small box and a large bucket. You fill both with marbles. The small box holds 25 marbles, and the large bucket holds 75 marbles. Which has the bigger volume?
Solution:* Volume is about how much space something takes up. The bucket holds more marbles, therefore takes up more space.
Answer:* The large bucket has a bigger volume.
Commentary:* The informal unit here is "marbles." Independent Practice (Questions Only)
Question 1: A square table has sides of 90 cm each. What is the perimeter of the table in centimetres?
Question 2: A rectangular window has a length of 1 meter and a width of 50 cm. What is the perimeter of the window in centimetres?