The little boat that could
Jowantedtosendapretendletteracrossawashing-upbowl.Dadputatowelunderthebowlandfoundapieceoffoil.Josqueezeditintoatightlump.‘Firstboat!’sheannounced.Itsank.Theletterstayedsafelyonthetable.
Dadfishedoutthefoilandaskedwhattheymightchange.Jospreaditout,thenfoldeduptheedgestomakeawidelittletray.Shelowereditgentlyontothewater.Thistimeitfloated.‘Samefoil,’shesaid,‘differentboat!’
‘Theboatshapemovesmorewaterasidebeforeitstopgoesunderwater,’Dadexplained.‘Thewatercanpushupenoughtobalanceitsweight.’Jowatchedthelittletray.Therewasplentyofspaceinsideitforairandanimaginarycaptain.Atightlumphadn'tmadethesameroomyshape.
Theygavetheboatapaperflag.ThenJopushedgentlyononeedge,lettingwaterspillin.Theboatsatlower.Shelifteditoutbeforeitsank,emptiedit,andtriedagain.Engineers,Dadsaid,oftenchangedadesignandtesteditmorethanonce.
Atlastthepretendlettercrossedthebowl.JoreadittoDad:‘DearCaptain,thankyouforthedelivery.’Thentheydriedthetableandputtheboatonashelf.Itsnextvoyagewouldhavetowaituntilafterlunch.
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Jo wanted to send a pretend letter across a washing-up bowl. Dad put a towel under the bowl and found a piece of foil. Jo squeezed it into a tight lump. ‘First boat!’ she announced. It sank. The letter stayed safely on the table.
Dad fished out the foil and asked what they might change. Jo spread it out, then folded up the edges to make a wide little tray. She lowered it gently onto the water. This time it floated. ‘Same foil,’ she said, ‘different boat!’
‘The boat shape moves more water aside before its top goes underwater,’ Dad explained. ‘The water can push up enough to balance its weight.’ Jo watched the little tray. There was plenty of space inside it for air and an imaginary captain. A tight lump hadn't made the same roomy shape.
They gave the boat a paper flag. Then Jo pushed gently on one edge, letting water spill in. The boat sat lower. She lifted it out before it sank, emptied it, and tried again. Engineers, Dad said, often changed a design and tested it more than once.
At last the pretend letter crossed the bowl. Jo read it to Dad: ‘Dear Captain, thank you for the delivery.’ Then they dried the table and put the boat on a shelf. Its next voyage would have to wait until after lunch.
What we learned
A hollow boat can move enough water aside for the upward push to balance its weight. Shape matters.
