Post on 23-Dec-2015
transcript
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
are needed to see this picture.
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
are needed to see this picture.
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