How Big? How Heavy?
Class 5 · Mathematics
4 ideas in Class 5 Mathematics, explained in plain words, with games and quizzes to practise.
Volume by pushing up water
Part of: How big? Volume
Volume is the amount of space a thing takes up. When you drop a stone into a glass of water, the water rises because the stone needs room. A bigger stone makes the water rise more. Counting how much the water rises tells us the volume.
Why it matters. Children usually compare things by length or weight. Volume is a third idea and is easy to confuse with weight. Without it, it is hard to understand litres, mL, tanks and packing later on.
Try it in two minutes
- Fill a clear glass half full of water and put a rubber band around it at the water level.
- Ask your child to guess whether a lemon or a small potato will push the water up more. Drop each in one at a time and watch.
- Now drop in 5 small marbles or coins. Ask: how many marbles would make the water rise as much as the lemon did?
- Ask why the water rose even though nothing was poured in. Listen for the idea that the object needs space.
Try at home. Use a measuring cup with mL marks and find the volume of three small household things by checking how far the water rises.
Volume in centimetre cubes and layers
Part of: How big? Volume
A centimetre cube is a tiny cube with every side 1 cm. The number of such cubes that fill a solid is its volume. For a block, we count the cubes in one layer and multiply by the number of layers.
Why it matters. Counting units in layers is the first step to the formula for volume. Children who only add the sides often get wrong answers later.
Try it in two minutes
- Collect about 24 identical small blocks, sugar cubes or dice.
- Build a flat layer 4 blocks long and 3 blocks wide. Ask: how many blocks are in this layer?
- Build a second and third layer on top. Ask: how many blocks now? How did you count without counting one by one?
- Now build a different shape with the same number of blocks and ask which one has more volume.
Try at home. Stack empty matchboxes of the same size in different ways using exactly 24 boxes. Ask your child what stays the same.
Packing cubes in boxes
Part of: How big? Volume
To know how many small cubes fit in a box, imagine filling the bottom layer first. The bottom layer holds length × width cubes. Then multiply by the number of layers, which is the height in cm.
Why it matters. This idea is used for packing, storing and shipping goods. It also leads to the volume formula in higher classes.
Try it in two minutes
- Pick a small box and measure its length, width and height in cm with a ruler.
- Ask: how many 1 cm cubes fit along the bottom length? Along the width? So how many in the bottom layer?
- Ask: how many layers can we stack until we reach the top of the box?
- Have your child say the total and, if you have sugar cubes or dice, check by packing.
Try at home. Compare two boxes, such as a tea box and a soap box, and guess which can pack more cubes. Then work it out.
Weight in kilograms and grams
Part of: How heavy? Weight
We weigh small things in grams (g) and bigger things in kilograms (kg). One kilogram is 1000 grams. So 2 kg 250 g is the same as 2250 g. If every coin weighs the same, we can find how many coins are in a bag by dividing the bag's weight by the weight of one coin.
Why it matters. Shopping, cooking and travelling all use kg and g. Children who mix them up make big mistakes, like 5 kg being read as 500 g.
Try it in two minutes
- Use a kitchen scale. Weigh a packet of salt and a packet of rice, and write down both weights in g.
- Ask: how many grams are there in 1 kg? How many grams in 3 kg?
- Weigh a 1 kg bag of anything. Ask your child to tell you the weight of 4 such bags in kg and in g.
- If you have 10 identical coins, weigh them. Ask how heavy 1 coin is and how many coins would weigh 1 kg.
Try at home. Pack a small bag for a day trip and write the weight of each item in g. Find the total and say it in kg and g.
What your child will practise
- Packing cubes in boxes: Ocean Quick Fire (Quick Fire)
- Volume by pushing up water: Jungle Quick Fire (Quick Fire)
- Volume by pushing up water: Ocean Quest (Collect the Answer)
- Volume in centimetre cubes and layers: Jungle Puzzle (Clue Puzzle)
- Weight in kilograms and grams: Jungle Quest (Collect the Answer)
- Quiz: Packing cubes in boxes (8 questions)
- Quiz: Volume by pushing up water (8 questions)
- Quiz: Volume in centimetre cubes and layers (8 questions)
- Quiz: Weight in kilograms and grams (8 questions)