Lesson Notes By Weeks and Term v3 - Primary 3
Weight
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Weight
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Subject: General Mathematics
Class: Primary 3
Term: 1st Term
Week: 9
Theme: Mensuration And Geometry
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Watch on YouTubemeasure weights of objects in grams and kilograms; make meaningful comparison of weight of objects like rocks, minerals; appreciate the need for grams and kilogram as standard units of measure for transactions.
a. What is Weight? Weight is a measure of how heavy an object is. It tells us the force with which gravity pulls an object towards the Earth. Different objects have different weights. For example, a stone feels heavier than a feather. b.
Units of Weight: To measure weight accurately and consistently, we use standard units. The two primary standard units of weight for Primary 3 are: Gram (g): The gram is used to measure the weight of lighter objects. Nigerian
Examples: A sachet of Milo, a small onion, a single kola nut, a pencil, a few groundnuts, a small fish, a seasoning cube, a small stone found by the roadside.
Kilogram (kg): The kilogram is used to measure the weight of heavier objects. Nigerian
Examples: A bag of rice, a tuber of yam, a cooking gas cylinder, a gallon of palm oil, a child, a bag of cement, a large rock. c.
Relationship between Grams and Kilograms: The kilogram is a larger unit than the gram. 1 kilogram (kg) = 1000 grams (g) This means that if an object weighs 1 kilogram, it is as heavy as 1000 grams. Similarly, 2 kg is 2000 g, and so on. d.
Measuring Instruments: To find the weight of an object, we use a weighing scale.
Common types of weighing scales include: Beam Balance (or Traditional Market Scale): This scale has two pans. The known weights (standard weights like 1kg, 500g, 200g) are placed on one pan, and the object to be weighed is placed on the other. When the beam is balanced (level), the weight of the object is equal to the sum of the standard weights. This is common in Nigerian local markets for selling food items.
Spring Scale: This scale uses a spring that stretches or compresses when an object is placed on it. A pointer indicates the weight on a calibrated dial.
Digital Weighing Scale: These are modern scales that display the weight digitally (in numbers). They are common in supermarkets, pharmacies, and homes. e.
Comparing Weights: To compare weights means to determine which object is heavier, lighter, or if they have the same weight.
Heavier than: An object is heavier if its weight is greater.
Lighter than: An object is lighter if its weight is smaller.
Same weight as: Two objects have the same weight if their measured weights are equal. f. Importance of Standard Units for Transactions: Standard units (grams and kilograms) are crucial for fairness and accuracy in buying and selling.
Fairness: They ensure that everyone pays the correct price for the exact amount of goods they receive, preventing sellers from giving less or buyers from demanding more than paid for.
Consistency: The weight of 1 kg is the same everywhere, whether in Lagos, Kano, or Port Harcourt. This consistency makes transactions reliable.
Clarity: Using standard units avoids confusion and disputes between buyers and sellers. Worked
Examples: Example 1: Identifying Appropriate Units For each object, state whether its weight would likely be measured in grams (g) or kilograms (kg): a. A mobile phone b. A bag of beans c. A sachet of sugar d. A whole watermelon e.
A small pebble Solution: a.
A mobile phone: grams (g) (It is relatively light). b.
A bag of beans: kilograms (kg) (It is heavy). c.
A sachet of sugar: grams (g) (It is light). d.
A whole watermelon: kilograms (kg) (It is heavy). e.
A small pebble: grams (g) (It is light).
Example 2: Simple Conversion A market woman sells fish. One fish weighs 1500 grams. How many kilograms is this?
Solution: We know that 1000 grams = 1 kilogram. To convert grams to kilograms, we divide the number of grams by
1
0
0
0. Weight in kg = 1500 g / 1000 g/kg Weight in kg = 1.5 kg So, the fish weighs 1.5 kilograms.
Example 3: Comparing Weights A tuber of yam weighs 2 kg, and a bag of oranges weighs 1500 g. Which is heavier? * Solution: To compare, we must use the same units. Let's convert 1500 g to kg. 1500 fish weighs 1500 grams. How many kilograms is this?
Solution: We know that 1000 grams = 1 kilogram. To convert grams to kilograms, we divide the number of grams by
1
0
0
0. Weight in kg = 1500 g / 1000 g/kg Weight in kg = 1.5 kg So, the fish weighs 1.5 kilograms.
Example 3: Comparing Weights A tuber of yam weighs 2 kg, and a bag of oranges weighs 1500 g. Which is heavier?
Solution: To compare, we must use the same units. Let's convert 1500 g to kg. 1500 g = 1500 / 1000 kg = 1.5 kg Now we compare: Yam = 2 kg, Oranges = 1.5 kg. Since 2 kg is greater than 1.5 kg, the tuber of yam is heavier than the bag of oranges.
Materials: Assorted objects of varying weights (e.g., small rocks, larger stones, sachet milk, small empty bottle, book, pen, school bag, a tuber of yam/potato, bag of garri/rice (if available)). Weighing scales (beam balance, kitchen scale, or digital scale - if available, otherwise pictures/diagrams). Standard weights (e.g., 1kg, 500g, 200g, 100g – if using a beam balance). Chart paper/exercise books for recording.
Teacher Activities: Introduction (Engage): Begin by asking learners questions about "heaviness" and "lightness" of common objects. "Which is heavier, your pen or your school bag?" "How do we know?" Introduce the term "weight." Concept Explanation: Explain what weight is. Introduce grams (g) and kilograms (kg) as standard units. Provide numerous local examples for each.
Emphasize the relationship: 1 kg = 1000 g.
Demonstration of Measurement: If a physical weighing scale is available (especially a beam balance or kitchen scale), demonstrate how to use it. Show how to place objects on the scale and read the measurement. Demonstrate weighing a light object (e.g., a pen) and a heavier object (e.g., a book or a small rock), pointing out whether the reading is in grams or kilograms. If only pictures are available, explain how each type of scale works.
Practical Activity Guidance (Measurement): Divide learners into small groups. Provide each group with a set of objects and (ideally) a weighing scale. Instruct learners to weigh each object and record its weight in a chart, noting the unit (g or kg). Supervise groups, providing assistance and correcting errors in measurement or recording.
Practical Activity Guidance (Comparison): After measuring, guide learners to compare the weights of different objects from their recorded data. "Which object did your group find to be the heaviest? The lightest?" "Compare the weight of Object A and Object B, which is heavier?" Specifically, provide samples of different sizes of rocks and minerals (e.g., small gravel, a medium-sized stone, a larger rock) for them to weigh and compare.
Discussion on Standard Units: Lead a discussion on why standard units (g and kg) are important, especially in Nigerian markets for buying and selling food items (e.g., rice, beans, fish). Explain the concept of fairness in transactions.
Reinforcement: Ask questions to check understanding throughout the lesson.
Student Activities: Participation: Actively participate in the initial discussion about heaviness and lightness.
Observation: Observe the teacher's demonstration of weighing objects using the scale.
Group Work: Work in assigned groups to: Handle and estimate the weights of various objects. Take turns weighing objects using the provided scale. Accurately read and record the weights of objects in grams or kilograms in a provided chart/exercise book. Identify whether each object is measured in grams or kilograms.
Comparison: Compare the recorded weights of different objects (including rocks and minerals) and determine which is heavier, lighter, or if they are of similar weight.
Discussion: Participate in class discussions on the importance of standard units in daily life and market transactions.
Question 1: Which unit of weight would you use for each of these items, grams (g) or kilograms (kg)? a. A sachet of tomato paste b. A bag of cement c. A piece of jewel (e.g., a small earring) d.
A large yam tuber Solution 1: a.
A sachet of tomato paste: grams (g) (It is a small, relatively light item). b.
A bag of cement: kilograms (kg) (It is a heavy construction material). c.
A piece of jewel: grams (g) (Jewellery is very light and often measured in much smaller units, but for P3, grams is appropriate). d.
A large yam tuber: kilograms (kg) (Yams are a staple food and often quite heavy).
Commentary: This question assesses the learners' ability to choose appropriate units for common objects, directly addressing objective
1. Question 2: A small rock found in the school compound weighs 350 grams. A larger rock weighs 1 kilogram. Which rock is heavier? Show your working.
Solution 2: To compare their weights, we need to use the same unit. Let's convert 1 kilogram to grams. 1 kilogram (kg) = 1000 grams (g). So, the larger rock weighs 1000 grams. Comparing 350 grams (small rock) and 1000 grams (larger rock). Since 1000 grams is greater than 350 grams, the larger rock is heavier.
Commentary: This question requires learners to convert between units and then compare, linking to objectives 1 and 2, and using a relevant object (rock).
Question 3: Imagine you are at the market. A seller uses a weighing scale. He places a piece of meat on the scale, and the scale shows "750g". a. Is 750g closer to 1 kilogram or half a kilogram? b. Why is it important for the seller to use a scale and give you the correct weight?
Solution 3: a. We know that 1 kilogram = 1000 grams, and half a kilogram (0.5 kg) = 500 grams. 750g is halfway between 500g and 1000g.
Therefore, 750g is closer to both 1 kilogram (1000g) than half a kilogram (500g), but it's more specific to say it's 3/4 of a kilogram. For a P3 student, they should understand 750g is heavier than half a kilogram and less than 1 kilogram. If they say it's more than half a kilogram and less than a kilogram, that's a good understanding. More precisely, it's 250g away from 500g and 250g away from 1000g. So, it is exactly in the middle of half a kilogram and one kilogram.
Teacher note: Accept answers that show understanding of its position relative to 500g and 1000g. b. It is important for the seller to use a scale and give the correct weight to ensure fairness in the transaction. This way, the customer pays exactly for the amount of meat they receive, and the seller also gets paid fairly for their goods. It builds trust.
Commentary: This question connects measurement to real-life market scenarios and reinforces the appreciation for standard units and fair transactions (objective 3).
Example 1: Identifying Appropriate Units
For each object, state whether its weight would likely be measured in grams (g) or kilograms (kg):
a. A mobile phone
b. A bag of beans
c. A sachet of sugar
d. A whole watermelon
e. A small pebble
Solution:
a.
A mobile phone: grams (g) (It is relatively light).
b.
A bag of beans: kilograms (kg) (It is heavy).
c.
A sachet of sugar: grams (g) (It is light).
d.
A whole watermelon: kilograms (kg) (It is heavy).
e.
A small pebble: grams (g) (It is light).
Example 2: Simple Conversion
A market woman sells fish. One fish weighs 1500 grams. How many kilograms is this?
Solution:
We know that 1000 grams = 1 kilogram.
To convert grams to kilograms, we divide the number of grams by
1
0
0
0.
Weight in kg = 1500 g / 1000 g/kg
Weight in kg = 1.5 kg
So, the fish weighs 1.5 kilograms.
Example 3: Comparing Weights
A tuber of yam weighs 2 kg, and a bag of oranges weighs 1500 g. Which is heavier?
Solution:
To compare, we must use the same units. Let's convert 1500 g to kg.
1500 g = 1500 / 1000 kg = 1.5 kg
Now we compare: Yam = 2 kg, Oranges = 1.5 kg.
Since 2 kg is greater than 1.5 kg, the tuber of yam is heavier than the bag of oranges.
Teaching and Learning Activities
Materials:
Assorted objects of varying weights (e.g., small rocks, larger stones, sachet milk, small empty bottle, book, pen, school bag, a tuber of yam/potato, bag of garri/rice (if available)).
Weighing scales (beam balance, kitchen scale, or digital scale - if available, otherwise pictures/diagrams).
Standard weights (e.g., 1kg, 500g, 200g, 100g – if using a beam balance).
Chart paper/exercise books for recording.
Market Transactions and Commerce (Economics): This is perhaps the most direct and frequent application in Nigeria. Learners understand how weighing scales are used in local markets (e.g., "Oja," "Eke," "Kasuwa") to sell items like rice, beans, yam, garri, meat, and fish. Understanding weight ensures that customers get the correct quantity for the money they pay, preventing cheating and promoting fair trade. It integrates with financial literacy and consumer education. Household Activities and Cooking (Home Economics): Many cooking recipes, especially for baking or specific dishes, require ingredients to be measured by weight (e.g., "add 250g of flour," "100g of sugar"). Understanding grams helps in following recipes accurately. Also, household items like detergent, cooking oil, and packaged foods have their weights labeled in grams or kilograms, informing consumers about product quantity. Health and Personal Care (Science/Health Education): Weight measurement is vital in health. Babies are weighed at birth and regularly thereafter to monitor their growth and health status. Medication dosages are often prescribed based on a patient's weight. Over-the-counter products like body creams and ointments often indicate their quantity in grams.