Let's Learn About Weight! (g/kg)

Hello, young mathematicians! Have you ever tried to pick up your school bag and thought, "Wow, this is heavy!"? Or have you ever held a tiny feather and thought about how light it is? That feeling of 'heavy' or 'light' is what we call weight. In this chapter, we're going to become experts at understanding and measuring weight. It's a super useful skill for cooking, shopping, and so much more!


Section 1: What is Weight?

Weight is simply a measure of how heavy or light an object is.

Imagine you have a tennis ball and a bowling ball. Which one is harder to lift? The bowling ball, right? That's because it has more weight. It's heavier!

Key Takeaway

When we talk about weight, we're talking about how heavy something is.


Section 2: Comparing Weight

There are a few easy ways to figure out which of two objects is heavier.

Comparing by Feeling (Intuitive Comparison)

You can use your own hands as a scale! Try this:

1. Pick up a pencil in one hand.
2. Pick up a book in your other hand.
3. Which hand feels like it's working harder? The one holding the book!

The book feels heavier than the pencil. You just compared their weights intuitively! Easy, right?

Comparing with a Balance Scale (Direct Comparison)

A balance scale is a tool that helps us compare weights accurately. It has two sides. When you put an object on each side:

  • The side that goes down holds the heavier object.
  • The side that goes up holds the lighter object.
  • If the two sides are perfectly level, the objects have the same weight!

Example: If you put an apple on one side and an eraser on the other, the side with the apple will go down because it's heavier.

Comparing with Fun Units (Improvised Units)

What if we don't have special weights? We can use everyday objects! These are called improvised units.

We could use a balance scale to see how many marbles weigh the same as a toy car. If it takes 15 marbles to make the scale level with the car, we can say:

The weight of the toy car is 15 marbles.

It's important to choose the right improvised unit. You wouldn't measure a heavy book using tiny grains of sand, but you could use building blocks!

Key Takeaway

We can compare weight by feeling it, by using a balance scale, or by measuring with improvised units like marbles or paperclips.


Section 3: Standard Units - Grams and Kilograms

Using marbles is fun, but everyone's marbles might be a different size! To make sure we all measure the same way, we use standard units. The two most important units for weight are the gram and the kilogram.

The Gram (g) - For Light Things

A gram is very light. Think about the weight of a single paperclip. That's about 1 gram!

We use grams to measure things that are not very heavy.

  • A single piece of paper
  • A small coin
  • A strawberry

The short way to write gram is g. So, 10 grams can be written as 10 g.

The Kilogram (kg) - For Heavy Things

A kilogram is much heavier than a gram. A big bag of sugar or a large bottle of juice often weighs 1 kilogram.

We use kilograms to measure heavier things.

  • A big watermelon
  • Your school bag with all your books
  • A small dog

The short way to write kilogram is kg. So, 5 kilograms can be written as 5 kg.

The Magic Connection: 1000!

Here is the most important rule to remember. It's the secret that connects grams and kilograms!

There are 1000 grams in 1 kilogram.

$$1000 \text{ g} = 1 \text{ kg}$$

Memory Trick: Imagine 1000 tiny paperclips (1 g each) all huddled together. They would weigh the same as one big bag of sugar (1 kg)!

Key Takeaway

We use grams (g) for light things and kilograms (kg) for heavy things. The magic rule is 1 kg = 1000 g.


Section 4: Measuring and Recording Weight

We use weighing scales to find the exact weight of things. Now let's learn how to write down what we measure.

Writing Weight in kg and g

Sometimes, things aren't an exact number of kilograms. For example, a chicken might weigh more than 1 kg but less than 2 kg.

We would write its weight as a mix of kilograms and grams. For example:

1 kg 400 g

This means the chicken weighs 1 full kilogram and 400 extra grams.

Super Skill: Converting to Grams

You can also write a mixed weight using only grams. This is a very useful skill! Don't worry, it's easy if you follow the steps. Let's convert 2 kg 150 g into just grams.

Step 1: Look at the kilograms. We have 2 kg.

Step 2: Change the kilograms into grams. Remember, 1 kg = 1000 g, so 2 kg is 2 lots of 1000 g.

$$2 \text{ kg} = 2 \times 1000 \text{ g} = 2000 \text{ g}$$

Step 3: Now, add the extra grams from the original weight. We had 150 g.

$$2000 \text{ g} + 150 \text{ g} = 2150 \text{ g}$$

That's it! 2 kg 150 g is the same as 2150 g. You've got this!

Common Mistake Alert!

When you see 3 kg 50 g, don't write it as 350 g. Remember that the 3 kg part is a whole 3000 g! So, the correct answer is 3000 g + 50 g = 3050 g.

Key Takeaway

We can write heavy weights using both kg and g (like 3 kg 200 g). To turn this into just grams, change the kg to grams (3 kg = 3000 g) and then add the rest (3000 + 200 = 3200 g).


Section 5: Let's Estimate!

Estimating means making a smart guess. You don't need a scale to estimate, just your brain and your hands!

To get good at estimating, try to remember what certain weights feel like:

  • A paperclip is about 1 g.
  • A bag of sugar is 1 kg.

Now, pick up an object, like an apple. Does it feel much heavier than a paperclip? Yes. Does it feel lighter than a big bag of sugar? Yes. So you can estimate its weight is somewhere between 100 g and 200 g. The more you practice, the better your guesses will be!

Did you know?

The heaviest animal on Earth, the blue whale, can weigh up to 150,000 kg! That's as heavy as 30 elephants!


Chapter Review: Quick Facts!

Wow, you've learned so much! Here are the most important points to remember.

  • Weight tells us how heavy an object is.
  • We use grams (g) to measure light objects.
  • We use kilograms (kg) to measure heavy objects.
  • The golden rule is: $$1 \text{ kg} = 1000 \text{ g}$$
  • We can record weight in different ways, like 4 kg 250 g or 4250 g.
  • Estimating is making a smart guess about weight.

Keep practising by picking up things around your home and thinking about their weight. You're a weight expert now!