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Clay and Cargo
Vince wants to give his stones a ride. He reshapes a sinking lump of clay, watches his boat settle lower as he adds stones, and finds a smaller-load plan after water comes in. A quiet story about shape, floating and trying again.
Turn the pagesOr scroll to readA ride for the stones
Pages 1–2
My clay sinks. How will my stones ride?
Explore together · A sinking lump
Vince releases a solid clay lump into a shallow tub. It settles on the bottom while four stones wait on a blue cloth. The selected clay is denser than water. A solid lump sinks; the waiting stones give Vince a reason to try a different shape.
Ask together: What could Vince change about his clay?
A new shape
Pages 3–4
I press it wide. I turn the edges up.
Explore together · A hollow hull
Vince presses the same clay wide and turns its edges up into a broad bowl. An intact hollow shape can keep water out of a larger space. The raised edges and unbroken bottom matter; a wide solid pancake is not the same thing.
Ask together: Where could water get into a boat?
Same clay
Pages 5–6
Same clay. Now it floats!
Explore together · Floating after release
Vince lowers the empty clay bowl into the tub, then takes both hands away. It floats with a dry interior. The clay has not become lighter. A suitable bowl shape can displace enough water to support its weight before water reaches its rim.
Ask together: What changed, and what stayed the same?
A gentle press
Pages 7–8
I press gently. Up you come!
Explore together · Returning after release
Vince gently presses the empty bowl a little deeper, then lifts his fingers away. The bowl rises while remaining partly in the water. A slightly deeper intact boat displaces more water. If it stays level, dry and undamaged, the increased upward force can lift it again after release.
Ask together: What happens when Vince lets go?
More stones
Pages 9–10
A stone rides. More stones. Lower.
Explore together · A lower ride
One stone rides in the dry hull. With three stones aboard, the same boat sits lower in the water. Added cargo increases the weight. A floating hull settles deeper until the upward force balances its new total weight, provided it can still keep water out.
Ask together: Which boat has more rim above the water?
One more
Pages 11–12
One more... Water comes in!
Explore together · Water over the rim
Vince adds the last stone. Water crosses the low rim and enters the clay bowl. A low open rim can let water in when a load brings it down to the surface. The exact load depends on the clay, hull and stones; these counts are illustrative.
Ask together: Where does the water enter?
Ready again
Pages 13–14
Stones out. Water out. Ready to try again.
Explore together · Emptying and draining
Vince removes the stones and tips water out of the intact bowl. The empty dry hull can float again. Removing the cargo alone does not empty a flooded boat. Vince drains the water before relaunching the undamaged hull.
Ask together: What two things does Vince take out?
A smaller load
Pages 15–16
One small load. Then another trip.
Explore together · Several trips
Vince nudges a one-stone load across the tub, then lifts the stone out at the far blue cloth. Three stones still wait for later trips. A smaller load leaves more rim above water. Repeating a successful lighter trip gives Vince a way to carry the stones without trying to carry them all at once.
Ask together: How could the waiting stones get their rides?
Remembering the ride
Pages 17–18
For grown-ups
Pages 19–20
For Grown-Ups Vince changes one lump of clay into a boat, then discovers how a load changes its ride. His cargo is the stones he wants to carry. 1–6 A shape that floats This modeling clay is denser than water. A solid lump sinks. A broad watertight bowl can keep water out of a larger space without adding clay. At rest afloat, the upward force from the water balances the weight of the boat. The clay itself has not become lighter. 7–8 A little push Pressing an intact boat a little deeper makes it displace more water. If its rim stays above water, the increased upward force can lift it again when the fingers leave. Pressing too far, unevenly or on soft clay may tip, flood or damage it. 9–12 A growing load Added stones increase the total weight. The boat settles lower and displaces more water. Eventually water can come over the rim. The open clay hull floods and sinks; water pushes upward on sinking objects too, but here that push is not enough. 13–18 Another way to carry Vince removes the stones and drains the water from an intact hull before trying again. A smaller load leaves more rim above water. Several light trips can carry what one overloaded trip cannot. Explore together A grown-up stays beside a shallow tub and handles small objects. Use non-hardening, water-resistant modeling clay that first sinks as a lump. Help make a broad bowl with an unbroken bottom, then test it empty. Add smooth weights gently and spread them low. Dry and reshape as needed; empty the tub afterwards. These pictures show a possible sequence, not a tested recipe or load limit. Clay, thickness, shape and stone size change the result. Ask what changed, and watch together. Grey ticks suggest movement; they are not visible forces.
Open these pages in the readerSources and evidence
The selected dense non-hardening modeling clay sinks as a compact solid lump in water.
ACS Grade 5 Lesson 2.4: Density and Sinking and Floating, Teacher Background
The clay is selected to be denser than water; not every modeling material behaves the same way.
The same clay can float when formed into a broad watertight bowl whose above-water rim keeps water out and whose submerged envelope excludes enough water.
ACS Grade 5 Lesson 2.4: Density and Sinking and Floating, Teacher Background
The bowl needs an intact watertight bottom and raised rim, enough space to displace water, and a dry interior. Reshaping does not reduce the clay mass.
An intact stable empty floating bowl depressed gently without flooding can rise after the fingers separate.
OpenStax University Physics Volume 1, 14.4 Archimedes’ Principle and Buoyancy
The gentle press is conditional on a level, unchanged, dry hull with its rim above water. Soft clay can deform, tip or flood.
Adding cargo makes the same stable boat float deeper while its dry interior excludes more water; removing cargo before flooding can reduce the required immersion.
OpenStax University Physics Volume 1, 14.4 Archimedes’ Principle and Buoyancy
One, three and four stones are an illustrative sequence, not a tested load limit. Hull thickness, shape and stone size change the result.
If loading brings the rim low enough for water to enter, an open dense clay hull can flood and sink.
OpenStax University Physics Volume 1, 14.4 Archimedes’ Principle and Buoyancy
Water entry must occur at a rim low enough to be overtopped. Upward force also acts on sinking objects; it is insufficient to support this flooded dense hull.
Emptying the water and cargo from an undamaged hull restores the light-load conditions; carrying smaller loads in several trips can solve the cargo task.
ACS Grade 5 Lesson 2.4: Density and Sinking and Floating, Teacher Background
Vince removes the cargo and drains an intact hull before relaunch. Draining does not repair cracks. The story shows the first delivery and proposes later trips.
A story worth keeping?
Read it here as often as you like. The physical edition is coming soon.