Exploring buoyancy with aluminum foil boats and pennies
Aluminum foil boats and a handful of pennies are one of the most affordable, low-prep STEM activities a classroom can run. With a roll of foil, a plastic tub of water, and a stack of coins, students can test predictions, collect data, and watch a clear physical principle play out in front of them. The activity scales easily from a quick Year 3 science rotation to a whole-class investigation.
Australian teachers have long embraced this kind of hands-on experiment because it lines up neatly with the Science and Mathematics strands of the Australian Curriculum, particularly the inquiry skills of questioning, predicting, and recording. It also travels well, whether the lesson takes place in a suburban primary school in Brisbane, a regional campus near Dubbo, or a kitchen table in Hobart during remote learning weeks.
At its core, the experiment is a living demonstration of Archimedes' principle: an object floats when the weight of the water it displaces equals or exceeds its own weight. Aluminium foil is light, malleable, and water-resistant, making it an ideal vessel for the challenge. The more pennies a boat can hold before sinking, the more carefully students have designed its hull to displace water.
Below is a quick comparison of common hull designs students might try, along with average penny loads from typical classroom trials. It is a useful reference before launching the investigation.
| Hull design | Estimated max pennies | Strengths | Watch out for |
|---|---|---|---|
| Flat rectangle | 5–10 | Quick to fold, good control variable | Sits low in the water, edges can spill |
| Shallow tray | 15–25 | Stable base, easy to load | Sides can buckle under weight |
| Deep bowl | 25–40 | High displacement, holds more pennies | Tips easily if weight is uneven |
| Multi-chamber boat | 30–45 | Resists sinking even if one section floods | Takes longer to construct |
The physics behind the floating foil
When a foil boat rests on water, it pushes the liquid aside, and the water pushes back with an equal force. That upward push, called buoyancy, supports the boat and everything inside it. As pennies are dropped in, the combined weight grows, and the hull sinks deeper to displace more water. The moment the downward force of the load exceeds the maximum buoyant force, the boat plunges.
Density is the hidden variable in this experiment. Aluminium foil has a density of around 2.7 g/cm³, far greater than water, yet the air trapped inside the hull keeps the overall density below 1 g/cm³. The shape of the boat, not the material alone, controls whether it floats. The same strip of foil scrunched into a ball will sink immediately because it displaces almost no water.
Students often notice that wider, flatter boats float well but hold little, while deeper hulls can carry more weight before submerging. Encourage them to think of a real vessel, such as a ferry across Sydney Harbour, to make the link between classroom science and the wider world. A short discussion of how ferry designers balance cargo capacity with stability deepens the inquiry.
Setting up the experiment
The setup is refreshingly simple. Each group needs a sheet of aluminium foil about 30 cm square, around 50 clean pennies, a deep plastic container or takeaway tray, and access to water. A measuring jug, paper towels, and a marker for labelling rounds round out the kit. Teachers in Australian schools should check their local Work Health and Safety guidelines: spills on hard floors should be wiped promptly, and electrical appliances should be kept well away from the water station.
Guide students through folding their first hull, then challenge them to redesign it after each round. Recording results on a simple table, such as the one from sink and float experiments, turns the activity into genuine scientific inquiry rather than a one-off craft. Allow two or three design cycles so pupils can test, refine, and retest.
Predicting and counting pennies
The mathematics embedded in this activity is just as rich as the science. Students can estimate how many pennies a hull might hold, count actual loads, calculate differences between designs, and graph the results. Fractions come alive when a boat holds 18 out of a possible 30 pennies, and decimals appear naturally when comparing 0.6 kg of coins against a kilogram total. Teachers looking for a tight numeracy link can pair the activity with resources such as third grade fraction strips to reinforce part-whole thinking.
Encourage learners to record each trial as a proper scientific entry: hull design, predicted pennies, actual pennies, and a one-sentence reflection. Comparing designs across the class produces a rich data set for graphing and average calculations, both key content descriptors in the Mathematics strand of the Australian Curriculum.
Linking to the Australian Curriculum
For Years 3 to 6, the activity maps directly to the Science Understanding strand involving solids, liquids, and forces, as well as the Inquiry Skills strand. Older students can extend into calculating density, exploring surface area and volume, or designing foil vessels that float in saltwater versus freshwater. The cross-curricular reach extends into HASS, where students can research maritime trade in Australian ports such as Fremantle or Newcastle, and into Health, where they discuss water safety around rivers and beaches.
Extending the activity
Once students have mastered pennies, the same hulls can be tested with different cargo: marbles, paper clips, or small plastic bears. Outdoor learning works beautifully here; a sturdy plastic tub on a verandah or in a school courtyard lets larger groups rotate through the challenge. Some Brisbane teachers take the activity further by linking it to local creek studies, comparing how objects behave in still water versus slow-moving streams. With a small tweak, the same investigation becomes a week-long project that combines physics, mathematics, design thinking, and a touch of Australian maritime history.