Measurement (weight)
What is Weight?
Weight tells us how heavy or light an object is. We measure weight to know the heaviness of objects, like how much a bag of rice weighs or how heavy a watermelon is.
Units of Weight
In Class 3, students primarily learn about the metric system to measure weight. Here are the main units:
1. Gram (g):
-Gram is a small unit of weight.
– We use grams to measure light objects like a pencil, an apple, or a piece of chocolate.
2. Kilogram (kg):
– Kilogram is a larger unit of weight.
– 1 kilogram = 1000 grams.
– We use kilograms to measure heavier things like a bag of rice, a watermelon, or a school bag.
How to Measure Weight
We use different tools to measure weight:
Weighing scale: This tool is commonly used to measure weight. You might see it in stores or at home, where people use it to weigh fruits, vegetables, or themselves.
Converting Between Grams and Kilograms
Students also learn how to switch between these two units:
1 kilogram = 1000 grams
– To convert kilograms into grams, we multiply by 1000.
– To convert grams into kilograms, we divide by 1000.
Example 1:
If a bag of sugar weighs 2 kilograms, how many grams is it?
– 2 kg = 2 × 1000 = 2000 grams**
Example 2:
If a book weighs 500 grams, how many kilograms is it?
500 g = 500 ÷ 1000 = 0.5 kg
Examples of Measuring Weight:
1. An apple weighs about 150 grams.
2. A bag of flour weighs 2 kilograms.
3. A watermelon might weigh 5 kilograms.
Addition and subtraction of weight
Addition of Weight
When we add weights, we are finding the total weight of two or more objects. We can add weights in grams (g) or kilograms (kg), but we should make sure the units are the same before adding.
Example 1:
Mina has a bag of apples weighing 2 kilograms and a bag of oranges weighing 3 kilograms. What is the total weight of both bags?
Solution:
2 kg + 3 kg = 5 kg
Answer: The total weight is 5 kilograms.
Example 2:
A packet of biscuits weighs 150 grams, and a chocolate bar weighs 100 grams. What is the total weight?
Solution:
150 g + 100 g = 250 g
Answer: The total weight is 250 grams.
Subtraction of Weight
When we subtract weights, we find out how much lighter one object is compared to another, or how much weight remains after removing some weight.
Example 1:
A watermelon weighs 5 kilograms. If 2 kilograms of the watermelon is eaten, how much is left?
Solution:
5 kg – 2 kg = 3 kg
Answer: 3 kilograms of the watermelon is left.
Example 2:
A box of chocolates weighs 500 grams. If 200 grams of chocolates are removed, how much is left in the box?
Solution:
500 g – 200 g= 300 g
Answer: 300 grams of chocolates are left.
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Adding and Subtracting Weights with Different Units
If you need to add or subtract weights in kilograms and grams, you first need to convert everything into the same unit.
Example:
A bag weighs 2 kilograms and a book weighs 500 grams. What is their total weight?
1. Convert 2 kilograms to grams:
2 kg = 2000 g
2. Add the weights:
2000 g + 500 g = 2500 g
3. Convert back to kilograms, if needed:
2500 g = 2 kg, 500 g
Answer: The total weight is 2 kilograms 500 grams.
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Summary:
– To add weights, make sure the units are the same and then add them together.
– To subtract weights, make sure the units are the same and subtract them.
– Conversions between kilograms and grams might be needed when adding or subtracting weights.
Word problem
Example Word Problem:
“A watermelon weighs 2 kg, and an apple weighs 300 g. How much do both the watermelon and the apple weigh together in grams?”
Step-by-Step Solution:
1. Understand the Problem:
– You are given the weights of two objects: a watermelon (2 kg) and an apple (300 g).
– The question asks you to find the total weight in grams.
2. Convert to the Same Unit:
– Since the watermelon’s weight is in kilograms and the apple’s weight is in grams, you need to convert the watermelon’s weight to grams.
– 1 kg = 1000 g. So, 2kg = 2 x 1000 = 2000 g.
3. Add the Weights:
– Now, add the two weights together:
2000 g + 300 g = 2300 g.
4. State the Answer:
– The total weight of the watermelon and the apple is 2300 grams.
Key Concepts to Emphasize:
– Units of Weight: Kilograms (kg) and grams (g).
– Conversion: 1 kg = 1000 g.
– Addition: Add the converted weights together.