Mass: heavy and light
๐ In short
Which is heavier: a kilogram of feathers or a kilogram of iron? They're the same! Both are a kilogram. Mass measures how much matter is in something, and we measure it with scales, in grams, kilograms and tonnes.
๐คฉ Did you know?
- One liter of water has a mass of about one kilogram.
- The blue whale is the heaviest animal that has ever lived on Earth: more than 100 tonnes.
- A newborn baby has a mass of about 3 kilograms.
- The human heart has a mass of about 300 grams.
๐ Find out more
๐ Grams and kilograms
A gram is very small: a paper clip has a mass of about one gram. A kilogram is a thousand grams, like a bag of sugar or a one-liter bottle of water. We write them g and kg.
๐ Tonne
For very heavy things we use the tonne, which is a thousand kilograms. A small car is about a tonne, an African elephant can reach 6 tonnes, and a blue whale more than 100 tonnes!
๐ก Kinds of scales
A balance with two pans compares two things: the heavier pan goes down. Kitchen scales give us mass in grams, and bathroom scales measure our body's mass in kilograms.
๐ฏ Size isn't mass
A big balloon is light, and a small stone is heavy. Volume is how much space something takes up, and mass is how much matter is in it. So we can't judge weight by looking!
๐งฎ Worked examples
- 1 kg = 1000 gOne kilogram is a thousand grams.
- 1 t = 1000 kgOne tonne is a thousand kilograms.
- 2.5 kg = 2500 gTwo and a half kilograms.
๐ Key words
- Mass
- The amount of matter in something, measured with scales
- Kilogram
- A thousand grams, written kg
- Scales
- A tool for measuring mass
๐งช Try it at home
Make a balance with a coat hanger and two hanging bags. Compare: which is heavier, an apple or an orange? A spoon or a pencil? Then check with the kitchen scales.
๐งฉ Test yourself
1 How many grams are in a kilogram?
2 Which is heavier: a kilogram of feathers or a kilogram of iron?
3 What unit do we use for an elephant's mass?