Make a kilogram: grams and kilograms on a balance and on scales · Concept Studio

The idea

A kilogram is 1000 grams, and a litre of water has a mass of about one kilogram, so water and a balance give a feel for both units.

What you need

an equal-arm balance with a 1 kg mass and a set of gram masses (10 g, 20 g, 50 g, 100 g, 200 g, 500 g)
digital kitchen scales reading to 1 g
an empty 1 L bottle, a 250 mL measuring cup and water at room temperature
a bag of dry rice, zip-lock bags and a marker

How to do it

Put the 1 kg mass in one pan and fill a zip-lock bag with rice in the other pan until the pans level. Label the bag 1 kg. Check it on the kitchen scales.
Make bags of 50 g and 200 g the same way, then check each on the scales and record the reading.
Weigh the empty 1 L bottle on the scales, pour in four full 250 mL cups of water and weigh again. Subtract to find the mass of the water.
Pour 250 mL of water into the measuring cup on the scales (set to zero with the empty cup) and read the mass.
Heft the 1 kg bag, the 200 g bag and the 50 g bag with eyes closed and name each, then check.

What you should see

The rice bag balanced against the 1 kg mass reads close to 1000 g on the scales; any difference shows how finely the pans can be levelled. One litre of water at 20 degrees Celsius has a mass of 998 g (density 0.998 g per millilitre), so the bottle gains close to 1000 g; 250 mL of water reads about 250 g (249.5 g at that density). The scales show that 1 kg = 1000 g by reading 1000 g for the kilogram mass and switching display to 1.000 kg. The 50 g and 200 g bags read close to 50 g and 200 g on the scales.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

A kilogram is 100 grams.
Water has no mass because it is a liquid.

Safety card

Low riskLearners carry it out

Hazards

water near electrical scales
a 1 kg mass dropped on a foot

Controls

dry hands before touching the scales; lift the kilogram mass with two hands over the table

Note

No chemicals or heat are used, so the NSW Department of Education Chemical Safety in Schools package is not needed; ordinary classroom supervision under the school's usual risk management.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Mathematics K-10 Syllabus (2022), NSW Education Standards AuthorityMA2-NSM-01 MAO-WM-01
Australian Curriculum v9AC9M3M02AC9M4M01

Sources

The pages the author read to write this activity.