Does It Weigh Less When It Disappears?
- Chemistry
- Ages 8–11 · Grades 3–5
- Hands-on experiment
What you’ll find out
- Mass is how much matter there is; volume is how much space it takes up.
- Measuring is more reliable than looking, because things too small to see still have mass.
- When sugar dissolves or ice melts, the total mass stays the same.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Two different questions
Scientists ask two different questions about stuff. How much is there? A scale answers that, in grams, and it is called mass. How much space does it take up? A measuring jug answers that, in millilitres, and it is called volume. They are not the same: a bag of feathers can be as big as a bag of flour but much lighter. Eyes are easy to fool. A number on a scale is not fooled by how something looks.
Nothing is lost
Put a jug of water and a pile of sugar on the same scale: 500 grams of water and 20 grams of sugar make 520 grams. Stir the sugar in until it vanishes, then weigh again. The scale still reads 520 grams. The sugar did not disappear. It broke into bits far too small to see, and every bit still has mass. Melt ice in a sealed bag and the same thing happens: the look changes, but the mass stays the same.
Curriculum links: NGSS 5-PS1-2 · NGSS 5-PS1-3