Teaching with Boat Lab
For science and engineering teachers, co-op leaders and parents. One period on the foil boat challenge itself, one on why foil floats at all, what students get wrong and where the app answers it, and the sheet and the setup.
Using this with a class? Make a free class and add your students yourself: each gets a username and password, with no email or Google account needed. Or give them one join code. Using Google Classroom? Post the link there; with a free class, the link also puts each student in your class, so you see their work. mytekDev is also available from the Google Workspace Marketplace, so your school's Google admin can install it for everyone.A first lesson: One period: guess, load the first boat until it sinks, fold a better one from the same sheet, crumple the sheet into a ball, and load the best boat again in very salty water. Then compare the table.
Set up a free class Share to Google Classroom- About these notes
- Period one: the challenge
- Period two: why foil floats
- What students get wrong, and where the app answers it
- What the app simplifies, on purpose
- Grades 3 to 5, middle school and high school
- The sheet and the setup
- Standards
About these notes
Boat Lab is a clear tub of water and one square of kitchen foil. Students drag the fold lines to set the walls and the floor, fold the sheet into a boat, guess how many pennies it will hold, and add pennies until it sinks. Every trial lands in a table: the boat, the water, the guess, the count, and how it sank. A measuring cylinder catches the water each boat pushes aside, two arrows show the boat's weight and the water's push, and the same sheet can be crumpled into a ball.
The boat floats where the water it pushes aside weighs what the boat and its pennies weigh (Archimedes' principle), and it leans by the rule naval architects use for a box-shaped hull. With the ideal foil every count is exact: the same boat holds the same number every time, so students can compare designs fairly. A 15 cm sheet folded into a box with 1 cm walls holds 67 new pennies in tap water; with 2.5 cm walls it holds 99, and 119 in very salty water.
Period one: the challenge
- The first boat (10 minutes) Everyone opens the app: a low boat is already floating. Each student types a guess, then loads it until it sinks. It holds 67. Ask who was closest, and what they were watching as the boat went down: the water line on the ruler, climbing to the rim.
- Same foil, a better boat (15 minutes) Press Fold a new one. The rule is one sheet, nothing cut: students may only move the fold lines. Taller walls shrink the floor and wider floors need shorter walls. Each student tries at least three boats and guesses before each one. The graph under the tub plots pennies held against wall height; the top is near 2.5 cm, a sixth of the sheet, and the curve is flat there, so 2 cm walls lose only a few.
- Where the pennies go (10 minutes) Press Try again and tap every penny into one corner. The boat leans and floods long before it is full, often at 12 to 18 on the first boat, and about 17 to 20 on a boat with 2.5 cm walls. Spread them out levels it. This is the troubleshooting line on every foil boat handout, seen as a number.
- Compare (10 minutes) Put the best boats on the board. Same sheet, same pennies, same water: the only thing that changed is the shape, so the shape made the difference. Ask what the best boats have in common.
Period two: why foil floats
Start with Crumple it. The same sheet, squeezed into a tight ball, sinks at once. Ask what changed: not the foil and not its weight. The cylinder answers it. The ball pushed aside about a third of a milliliter of water, which weighs less than the ball (0.36 g against 0.97 g). A boat with 40 pennies pushed aside about 100 mL, which weighs exactly what the boat and its pennies weigh.
Turn on the two pushes. While the boat floats the arrows are the same length: balanced, so it does not move up or down. Add the last penny and the weight wins for a moment and the boat moves down. On the bottom the water's push is small, and the floor of the tub holds up the rest.
Then salt. Load the best boat in very salty water: about a fifth more pennies. Load it in sea water: only a few more, which is why the salt round in a real classroom is so often a disappointment. The water line close-up shows the boat sitting about half a millimeter higher in sea water. Salty water is heavier for its size, so the boat pushes aside less of it to hold the same load.
What students get wrong, and where the app answers it
| What students say | Where the app answers it |
|---|---|
| Heavy things sink, light things float | A 12 inch boat holds over 2 kg of pennies and floats; one penny on its own sinks. |
| It's the metal that decides | The same sheet floats as a boat and sinks as a ball. Same metal, same weight. |
| Air holds the boat up | The cylinder shows what does: the boat pushes aside its own weight of water. Nothing in the app says air lifts it. |
| A boat floats because its weight is spread out | Spreading the pennies matters for tipping, not for floating. What floats the boat is the room it takes up below the water line. |
| Flat things float | A raft with 0.3 cm walls holds far fewer than a box from the same sheet. |
| Things that sink have no push on them | On the bottom the up arrow is still there, just shorter than the weight. |
| Salt water holds more because it is thicker | Salt makes water a little thicker, but that is not why it holds more. Cooking oil is much thicker and holds fewer. What matters is that salt makes water heavier for its size. |
| The last penny is the one that counts | The table counts the pennies the boat held before the one that sank it, the way most class handouts do. |
What the app simplifies, on purpose
- In calm water the tub keeps the water still, and the ideal foil stays stiff and dry, so a real foil boat usually holds fewer. Real foil adds leaks at the creases, walls over 3 cm that slump, and pennies that sometimes land one spot over. Those are our own rules; nobody has measured a foil boat's leaks, and we found no published classroom counts.
- Every shape has upright walls. A dish is a short round pan, a canoe a six-sided box with pointed ends, and two hulls are two narrow boxes with a deck between.
- Pennies added with the buttons are set down spread out and treated as perfectly balanced. Only pennies a student taps into place lean the boat.
- The lean is worked out as if the whole floor stays in the water. A boat loaded on one side can lift its far edge out, and then a real boat leans further and holds even fewer.
- Surface tension is worth about one penny on a 10 cm boat. Water's temperature changes the count by less than one penny on a small sheet and three or four on a 12 inch sheet. Both are left out.
- Waves follow a rule of our own: ripples are 0.4 cm and choppy water 1 cm from crest to trough, and a wave washes over once the rim sits less than half a wave above the still water line. The point it makes is real: a boat in waves needs more rim above its water line, so low boats lose the most.
- Gram cubes are plastic a little heavier for its size than tap water, so a boat full of them sinks in tap water but would float awash in very salty water; the app keeps them out of water that salty and says why.
Grades 3 to 5, middle school and high school
| Grades 3 to 5 | Middle school | High school | |
|---|---|---|---|
| Shapes and sheets | Box and dish; 10 and 15 cm sheets | Box, dish, canoe, two hulls; four sheets up to 12 inches | The same |
| Waters | Tap and very salty | Seven, and a salt slider in grams per liter | The same |
| Cargo | New pennies | New and old pennies, washers, gram cubes, marbles | The same |
| Forces | Two arrows, no numbers | In newtons | In newtons, with the buoyant force written out as rho g V |
| Density | Heavier or lighter for its size, no numbers | Each water's density, and the whole boat's | The same, with the boat cut across to show G, B and M |
| Graph | Pennies held against wall height | The same | With a dashed curve of what the sheet holds at every wall |
| Code | Not shown | Write the lab's rules: how deep a boat sits, how many a box holds, the best wall | The same |
The sheet and the setup
The Sheet in the app's header is the student's write-up: their own question, every trial with the graph, and the questions. Hand in needs an answer to every one. They hand it in and it saves with the project, or print it. Print the build sheet gives a one-page plan for building foil boats for real, with a column for what the app said.
Setup sets the level, which sheets, shapes, waters and cargo are on the shelves, whether the foil is ideal, always real, or the student's choice, whether a guess is required before the first penny, whether the puzzles are on, which questions are on the sheet, and up to ten of your own. It prints an answer key with the count for every boat in 0.5 cm steps. Set it on a starter project and hand that out: the setup travels with it.
Standards
No NGSS performance expectation names buoyancy, and grade 5's matter standard keeps density out of its assessment. These are the ones the work fits, each kept inside its boundary.
- 3-5-ETS1-1 to 3: a criterion, a constraint, fair tests and failure points. 3-5-ETS1-3 most of all.
- MS-ETS1-1 to 4, and MS-ETS1-4 most of all: a model that generates data to test and improve a design.
- MS-PS2-2 (one dimension, one change at a time): the two vertical forces, balanced while the boat floats and unbalanced at the last penny.
- 3-PS2-1 at the grades 3 to 5 level: balanced and unbalanced, compared by the arrows' lengths, with no numbers.
- 5-PS1-3 for making observations and measurements, with its boundary kept: no density and no mass against weight at that level.
- Texas 5.6A (relative density, with water as the reference), 6.6D (density relative to various fluids) and 6.7B (net force in a vertical direction); Massachusetts 6.MS-PS1-7(MA).
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Page last reviewed November 2026.
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