Welcome class! Today, we are going to learn all about Mass. By the end of this lesson, you will be a measurement master! Let's dive in. 🚀
Have you ever picked up a packet of tea and wondered how heavy it is? The mass of an object is a measure of the amount of matter inside that object[cite: 1]. Whether it's a tiny leaf or a huge sack of rice, everything has mass!
To find out the mass of an object, we use scales! Here are a few common tools you might see in a shop or in your home:
This classic tool has a center beam and two hanging pans. You place the object you want to measure into one pan, and heavy metal blocks called standard weights into the other pan. When the beam across the top becomes perfectly straight (horizontal), it means the mass on both sides is exactly the same![cite: 1]
These are the heavy metal blocks used with the balance scale[cite: 1]. They come in specific sizes stamped right on them, like 50 g, 100 g, 500 g, 1 kg, 2 kg, and even 5 kg. You can mix and match them to figure out the exact mass of your items.
Sometimes, standard weights aren't enough (like when measuring exactly 425 g of a pumpkin)[cite: 1]. That's when we use a digital kitchen scale! It has a flat top and a small screen that quickly shows the exact mass in numbers. There are also larger scales you can stand on to check your own body mass[cite: 1]!
We use specific units to measure mass[cite: 1]. The two most common units you will see at the market are:
Example A: A small packet of tea leaves might have "50 g" written on it. This means its mass is 50 grammes[cite: 1].
Example B: A large bag of rice might weigh "50 kg"[cite: 1].
Sometimes we need to change kilogrammes into grammes, or grammes into kilogrammes. It's just like translating a language!
Here is the magic rule you must remember:
Example 1: Express 7 kg in grammes.
Solution: 7 x 1000 = 7000 g[cite: 1].
Example 2: Express 9000 g in kilogrammes.
Solution: 9000 / 1000 = 9 kg[cite: 1].
When you are baking a cake, you mix ingredients together. To find the total mass, we add! If you eat some of the cake, the mass decreases, so we subtract.
Adding: Always add grammes to grammes, and kilogrammes to kilogrammes[cite: 1]. If your grammes add up to 1000 or more, carry 1 kg over to the kilogramme column[cite: 1]!
Subtracting: Write them one below the other[cite: 1]. If you don't have enough grammes to subtract from, "borrow" 1 kg from the kg column and turn it into 1000 g, just like standard borrowing in math[cite: 1]!
Example Add: 1 kg 500 g + 1 kg 250 g
Solution: Add grammes: 500 + 250 = 750 g. Add kg: 1 + 1 = 2 kg. Answer: 2 kg 750 g.
Example Subtract: 2 kg 250 g - 0 kg 750 g[cite: 1]
Solution: You can't subtract 750 from 250. Borrow 1 kg! Now you have 1 kg left, and your grammes become 1000 + 250 = 1250 g[cite: 1]. Now subtract: 1250 - 750 = 500 g. Answer: 1 kg 500 g[cite: 1].