Lesson Notes By Weeks and Term v5 - Grade 4

Lesson Video

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Performance objectives

• Measure length in cm and m
• Measure mass in g and kg
• Measure capacity in ml and L
• Solve word problems using measurement
• Convert between units (like cm to m)

Lesson summary

This week, we're diving into the world of measurement! We will be looking at how we measure length, mass (how heavy something is), and capacity (how much something can hold). Understanding measurement is incredibly important in our daily lives here in South Africa. For example, when you're helping your family cook, you need to measure ingredients like sugar and flour. When you go shopping, you need to understand how much of something you are buying (like a litre of milk or a kilogram of potatoes). And when you're building something or arranging furniture, you need to measure the length of things to make sure they fit.

Lesson notes

Length Length tells us how long something is. We use different units to measure length depending on how big the object is.

Centimetre (cm): We use centimetres to measure smaller things, like the length of a pencil or a book. Think of a centimetre as being roughly the width of your little finger.

Metre (m): We use metres to measure larger things, like the height of a door or the length of a classroom. 1 metre is equal to 100 centimetres. So, 1 m = 100 cm.

Example 1: Measuring the length of a book. Let's say you want to measure the length of your Maths textbook. You would use a ruler that has centimetres marked on it. Place the "0" mark of the ruler at one end of the book. Then, look at where the other end of the book reaches on the ruler. If it reaches the 25 cm mark, then the length of the book is 25 cm.

Example 2: Converting centimetres to metres. A table is 150 cm long. How long is it in metres? Since 1 m = 100 cm, we can divide the length in centimetres by 100 to find the length in metres. 150 cm ÷ 100 = 1.5 m So, the table is 1.5 metres long. Mass Mass tells us how heavy something is. We also use different units to measure mass.

Gram (g): We use grams to measure the mass of lighter things, like a paperclip or a biscuit.

Kilogram (kg): We use kilograms to measure the mass of heavier things, like a bag of potatoes or a person. 1 kilogram is equal to 1000 grams. So, 1 kg = 1000 g.

Example 3: Measuring the mass of a bag of apples. You have a bag of apples and want to know its mass. You would use a scale. Place the bag of apples on the scale. The scale will show the mass in kilograms (kg) or grams (g). If the scale shows 2 kg, then the mass of the apples is 2 kilograms.

Example 4: Converting grams to kilograms. A bag of sugar has a mass of 5000 g. How much does it weigh in kilograms? Since 1 kg = 1000 g, we can divide the mass in grams by 1000 to find the mass in kilograms. 5000 g ÷ 1000 = 5 kg So, the bag of sugar has a mass of 5 kilograms. Capacity Capacity tells us how much a container can hold.

Millilitre (ml): We use millilitres to measure the capacity of smaller containers, like a medicine spoon or a small bottle of juice.

Litre (L): We use litres to measure the capacity of larger containers, like a bottle of water or a bucket. 1 litre is equal to 1000 millilitres. So, 1 L = 1000 ml.

Example 5: Measuring the capacity of a cup. You want to find out how much water a cup can hold. You would use a measuring jug that has millilitres marked on it. Pour water into the cup until it is full. Then, pour the water from the cup into the measuring jug. Read the mark on the jug to see how many millilitres of water were in the cup. If the water reaches the 250 ml mark, then the capacity of the cup is 250 ml.

Example 6: Converting millilitres to litres. A bottle contains 2000 ml of juice. How many litres of juice are in the bottle? Since 1 L = 1000 ml, we can divide the capacity in millilitres by 1000 to find the capacity in litres. 2000 ml ÷ 1000 = 2 L So, the bottle contains 2 litres of juice. Guided Practice (With Solutions)

Question 1: A piece of rope is 3 metres long. How long is the rope in centimetres?

Solution: We know that 1 metre (m) = 100 centimetres (cm) So, 3 metres = 3 100 centimetres 3 100 = 300 Therefore, the rope is 300 cm long.

Commentary: This question tests the understanding of the conversion between metres and centimetres. We used multiplication because we are converting from a larger unit (metres) to a smaller unit (centimetres).

Question 2: A packet of Simba chips has a mass of 120 grams. A bag of mealie meal has a mass of 2 kilograms. Which is heavier, and by how much in grams?

Solution: First, we need to convert the mass of the mealie meal to grams: 2 kg = 2 1000 g = 2000 g Now we can compare: 2000 g (mealie meal) is heavier than 120 g (Simba chips). To find the difference, subtract: 2000 g - 120 g = 1880 g Therefore, the mealie meal is heavier by 1880 grams.

Commentary: This question involves converting units and comparing mass. We converted kilograms to grams to make the comparison easier.

Question 3: A small bottle of Coke has a capacity of 300 ml. How many small bottles of Coke would you need to fill a 1.5 Litre bottle?

Solution: First, convert the capacity of the large bottle to millilitres: 1.5 L = 1.5 1000 ml = 1500 ml Now, divide the capacity of the large bottle by the capacity of the small bottle: 1500 ml ÷ 300 ml = 5 Therefore, you would need 5 small bottles of Coke to fill the 1.5 Litre bottle.

Commentary: This problem involves conversion from Litres to Millilitres and then division to determine how many smaller bottles are needed to fill a larger one. Independent Practice (Questions Only) A table is 2.5 metres long. How many centimetres long is the table? A packet of sugar weighs 1.5 kg. A packet of salt weighs 750 g. Which is heavier? By how many grams? A jug contains 800 ml of water. If you pour out 350 ml, how much water is left in the jug?