Tim SendenDept Applied Mathematics

Research School of Physical Sciences and Engineering

Beach experimentsOr experiments you do when you should be at the beach…

How the tiny shape the mighty

Start with a game…

Look at the atomic level up to the grain level

• Singing sand• Avalanches• Building sand castles• Make silicon from sand

Why does physical chemistry matter?

The duck-o-meter(CSIRO 1950s)

How do you measure the efficiency of a detergent ?

Length scalesmetre

millimetremicrometre

nanometre

Clean sand sinks.Dirty sand “floats”Foam on surf

Back to the beach…

What is sand?

Where did it come from?

Granite weathers into components

Quartz,clays

& other minerals

Looking at clay first….

Why doesn’t muddy water clear?

Red blood cell(6 micrometres)

The Colorado

The Nile

TheGanges

A sand dune is another example of local interactions leading to large structures.

Now a little about packing…

• types of sand• how sand sorts• avalanches• singing sand

Angle of repose

Polluted sanddoesn’t squeak

Squeakers and boomersBoomers in desserts

Squeakers on beaches

Under flow grains can sort- a local interaction

Ant Lions use the angle of repose to trap their prey

In 1661 Kepler said about 1/4 of a box of oranges is empty.

In 1998 Hale proved him correct.

QuickTime™ and aYUV420 codec decompressor

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What sort of packing is this?

How do you measure how efficient the packing is?

The stick trick(using physics for profit)

The Brazil nut effect

In cone shaped container brazil nuts go to the top

So “buoyancy” is very complex

Osborne Reynolds, 1885

Why does the sand dry out around your footprints in wet sand?

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Force chains

The other stick trick&

a game

liquids

grains

wei

ght

volume

wei

ght

volume

Buoyancy doesn’t exist(unless there’s flow…)

Quicksand - a case of very loose packing

But you’ll never sink below your chest.You’re less dense than the water + sand, so you’ll always float. BUT……

Tar pits are a different story.- you’re always more dense than oil, so you’ll sink slowly to the bottom.

How to build a great sand castleWhy oil and beaches don’t mix

1 mm

QuickTime™ and aYUV420 codec decompressor

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How to build the strongest sand castle?

Water flows along corners and crevasses of clean sand.The tighter the crevasse the stronger the cohesion.Polluted sand doesn’t work.

Which is worse?a) Oil spilt on dry sand?b) Oil spilt on totally wet sand?c) Oil split on partially wet sand?

But where is the silicon ?

Hopefully, this is the only siliconever to be made around here !

Scale of Forces1 N ≈ force required to hold an apple against gravity1 mN ≈ force required to hold a postage stamp against gravity1 µN ≈ force required to hold an eye lash against gravity1 nN ≈ chemical bonds; force between clay particles in water10 pN ≈ a single H-bond; protein structures

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The Brownian danceTwo forces in balance• One repels• The other attracts

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micrometres

Na+Cl-

Salts also weather from rocks

What happens in water?

Why does it foam?

What happens to the muddy water?

CubicSame as salt (NaCl)

HexagonalSame as magnesium

But what about sand?

(Time for a little chemisty)

Si

O

O

Si

SiSiO

OO

O O

Hard, chemically stable, slightly soluble

Water loves to wet it.

O Si O

OH

HOH

Grains interact with each other

Compare the different sands

Ideas for next year - 2008

• More chemistry (bioluminescence, more fire, electrolyse water and explode H2/O2,

• Make quick sand in lab, do fluidised bed on the beach and sink kids??

• Title: Sun, surf and sun - three essential elements for experimental beach science.

• What makes a rip, physics of waves

Equipment listGeiger counter - ziron sandRice/stick/plastic cupsMagnesium powder, chips, HCl, and sand50 Ml measuring cylinderSparklers, lighterGrain separation gear (carbon shards and glass beads)CD case taped around edgesBlue dyed dodecane and eye dropperForce chain gameClayer water and alum sulfate