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THE PHYSICAL EDITION

Grains and Castles

Build with Vince as loose sand pours, damp sand clumps and a cup lifts away from a tower. Too much water sends the mixture running; dry sand changes it again. Compare the shapes, follow the repairs and see what happens when the castle dries.

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Explore the science

Grains that pour and pilePages 1–2

Vince fills a cup, then pours a stream of sand into a heap. Duck waits beside the tray. Sand is made of many small solid grains. Dry grains can move past one another as they pour, then stop in a heap.

Ask together: What shape does the sand make when it lands?

Support and slopePages 3–4

Vince pats the upside-down cup. When he lifts it, loose grains settle into a low heap. The cup supports the sand while it is inside. Ordinary dry play sand does not hold these steep moulded sides after the cup is removed; grains slide into gentler slopes.

Ask together: What changes when the cup lifts away?

Damp grains hold togetherPages 5–6

Water enters the bowl of sand. Vince then holds a rough clump on his open palm. In damp sand, tiny water contacts help pull grains together. The clump is visible; those tiny contacts are too small to see in the picture.

Ask together: How is the sand in his hand different from the pouring sand?

Moulding damp sandPages 7–8

The cup lifts clear of a small sand tower that keeps its shape. Damp sand can hold a moulded shape. Packing the grains into a small smooth cup helps, and a wider opening makes release easier.

Ask together: How is this lift different from the first one?

More water changes the resultPages 9–10

Vince adds more water to the bowl. The mixture pours out and spreads, while his first tower stays beside it. Adding enough water can make a sand mixture runny. More water does not always make a stronger castle.

Ask together: What can this mixture do that the tower cannot?

Changing the mixturePages 11–12

A cup of dry sand waits beside the runny mixture. After mixing, the cup is empty and Vince holds a clump again. Mixing in dry sand changes the proportion of grains and water. The amount needed depends on the materials and how they are mixed; there is no one perfect spoonful.

Ask together: What could Vince try if the mixture is still too runny?

Using a discoveryPages 13–14

Vince lifts the cup from a second tower, then moves Duck along the path between the two. He uses the same moulding idea again to finish his play space. The wider view shows the path and both towers together.

Ask together: Where could Duck go next?

A change as sand driesPages 15–16

At a later visit, the towers are lower rounded heaps. Vince loosens grains with his fingers. Water can leave sand by evaporation. As the sand dries, the grains lose the water contacts that helped hold them together. The timing and remaining shape depend on conditions.

Ask together: What is different from the two towers Duck first visited?

Sources and evidence

  1. Loose dry sand grains can pour and come to rest as a heap.

    MIT OpenCourseWare, The Environment of the Earth's Surface, Chapter10: Mass Wasting

    These pictures show ordinary mineral play sand. Grains remain solid when a pile pours.

  2. Ordinary dry loose sand does not keep the steep sides of the illustrated small cup mould when released.

    MIT OpenCourseWare, The Environment of the Earth's Surface, Chapter10: Mass Wasting

    Christof Lanzerstorfer (2019), The water content of sand required for the maximum strength for building sand castles, CJEES14(1):61–66

    Damp sand can hold steeper shapes than dry sand. The result depends on grain properties, packing and the amount of water.

  3. Adding and mixing a little water can make this sand clump and retain a packed moulded shape.

    Maryam Pakpour, Rheology of dry, partially saturated and wet granular materials, University of Amsterdam thesis, Chapter3

    Christof Lanzerstorfer (2019), The water content of sand required for the maximum strength for building sand castles, CJEES14(1):61–66

    The tiny water contacts are too small to see here. Use a short smooth mould with a slightly wider opening.

  4. A mixture with enough added water can become runny and fail to retain the cup shape.

    Maryam Pakpour, Rheology of dry, partially saturated and wet granular materials, University of Amsterdam thesis, Chapter3

    Christof Lanzerstorfer (2019), The water content of sand required for the maximum strength for building sand castles, CJEES14(1):61–66

    Enough added water can make the mixture runny. Its behaviour depends on the materials and water content; more water is not always better.

  5. Mixing more dry sand into the runny mixture can reduce the water-to-sand proportion and return it to a mouldable damp state.

    Christof Lanzerstorfer (2019), The water content of sand required for the maximum strength for building sand castles, CJEES14(1):61–66

    Maryam Pakpour, Rheology of dry, partially saturated and wet granular materials, University of Amsterdam thesis, Chapter3

    Mix dry sand in gradually. There is no fixed spoonful or recipe for every sand. Sand with clay or coatings can behave differently.

  6. After this clean sand dries, grains loosen again when Vince gently rubs its edge; water can have left by evaporation.

    Christof Lanzerstorfer (2019), The water content of sand required for the maximum strength for building sand castles, CJEES14(1):61–66

    Maryam Pakpour, Rheology of dry, partially saturated and wet granular materials, University of Amsterdam thesis, Chapter3

    USGS Water Science School, Evaporation and the Water Cycle

    Drying takes different amounts of time. The story makes no exact prediction of the drying time or remaining shape.

Water and Wind

Water and Wind, pages 1–2: Wind moves the pinwheel.

Spread 1 / 12

Wind tickles my cheek. Round goes my pinwheel.

Explore the science

Wind & forcesPages 1–2

Wind moves the pinwheel. Wind is moving air. Vince feels it on his cheek and sees it push the pinwheel's angled blades.

Ask together: What tells you that the air is moving?

Currents & eddiesPages 3–4

Water passes the rock. A leaf circles behind it. Most water passes the rock; some circles back in an eddy. Laminar flow is orderly; turbulence is irregular, mixing motion. A swirl alone cannot distinguish them.

Ask together: How does the leaf move compared with the water passing the rock?

Waves & energyPages 5–6

Waves spread from the stream. The duck bobs. The falling stream makes waves that carry energy outward and make the toys bob. The stream's current also carries toys along. Bobbing and drifting are different motions.

Ask together: What moves up and down? What moves along the pond?

BuoyancyPages 7–8

A duck floats. A pebble sinks. Water pushes upward on both objects. This buoyancy balances the duck's weight, but not the pebble's. The pebble's splash makes the rings on the next spread.

Ask together: Where is each object compared with the surface?

When waves meetPages 9–10

Two wave patterns approach one another. When gentle waves overlap, their heights add, briefly raising or lowering the surface. This interference does not erase the waves; they continue through one another.

Ask together: What might happen where the two patterns meet?

Surface tensionPages 11–12

Tiny dents appear beneath the strider’s legs. Surface tension helps support the strider where its water-repellent legs dent the water. The duck floats mainly by displacing water.

Ask together: What do you notice where its legs meet the water?

Suction & pressurePages 13–14

The duck bubbles, fills and squirts. Squeeze underwater: air bubbles out. Release with the opening submerged: the elastic duck springs back, lowering pressure inside. The surrounding water pressure pushes water in. Squeeze above water: water exits through that same opening.

Ask together: What changes when Vince squeezes and then lets go?

Lift & gravityPages 15–16

A paper plane glides forward and down. The throw starts the plane moving. Airflow around its wings produces lift and turns air downward. Gravity pulls down; drag resists motion. In still air, the plane glides forward and gradually descends.

Ask together: Where might the plane go next?

ViscosityPages 17–18

Milk runs. Honey stretches into a thread. Honey's greater viscosity means greater resistance to flow. It makes a slow thread while milk runs readily. Temperature and pouring method also matter; this snack is an observation, not a controlled test.

Ask together: How do the milk and honey move differently?

Draining & swirlingPages 19–20

Foam curves inward toward the drain. Gravity drives water through the drain. Existing turning motion can become a curved inward flow, traced by foam. Here water travels to the outlet, unlike waves crossing the pond. Not every drain swirls.

Ask together: Can you follow the foam toward the drain?

Scientific observationPages 21–22

Vince sketches what he noticed. Vince records something he noticed. Drawings, marks or words let him return to an observation. He does not need all the answers.

Ask together: Which earlier picture matches one of his drawings?

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