Heavier or lighter: comparing masses by hefting · Concept Studio

The idea

Mass is how much stuff is in an object, felt by hefting one object in each hand, and it is not the same as size.

Safety card

Low riskAn adult supervises

Hazards

glass marbles are a choking hazard
a dropped food tin can hurt toes

Controls

the bags stay tied while children heft them, and only the adult opens a bag, over the table, before counting the marbles back in
heft the objects over a 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.

What you need

a golf ball and a table-tennis ball
two identical opaque cloth bags, one holding 20 glass marbles and the other holding cotton wool
an empty cereal box and a 400 g food tin
paper and crayons for recording

How to do it

Hold the golf ball in one hand and the table-tennis ball in the other and say which feels heavier. Swap hands and check that the answer stays the same.
Look at the two cloth bags without opening them and predict which is heavier. Heft them to check, then the adult opens each bag over the table and shows what is inside, and the group talks about why the same-sized bags feel different.
Look at the empty cereal box and the food tin. Predict which is heavier and say why, then heft them to check.
Draw each pair and circle the object that felt heavier, using the words heavier and lighter.

What you should see

The golf ball (about 46 g) feels heavier than the table-tennis ball (about 2.7 g) although they are close in size, and swapping hands does not change the answer. The marble bag feels heavier than the cotton-wool bag although the bags look the same. The small tin (400 g of contents) feels heavier than the large empty cereal box, the pair where size and mass disagree most. In each pair one object is several times heavier than the other, so hefting settles it.

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.

The bigger object is always the heavier one.
Two things that look the same on the outside have the same mass.

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 AuthorityMAE-NSM-01 MAO-WM-01
Australian Curriculum v9AC9MFM01

Sources

The pages the author read to write this activity.