By: Honzoda Abidjanova

TABLE OF CONTENTS OOBLECK KETCHUP SILLY PUTTY FLUBBER CARAMEL CUSTARD BIBLIOGRAPHY THE END

WHAT IS OOBLECK ? Oobleck is a mixture of corn starch and water. The fun of oobleck is that it is a soquid. As a non-Newtonian fluid it is liquid until put under pressure where it acts as a solid.

An inexpensive, non-toxic example of a non-Newtonian fluid is a suspension of starch (e.g. cornstarch) in water, sometimes called "oobleck" or "ooze" (1 part of water to 1.5–2 parts of corn starch). [ Uncooked imitation custard, being a suspension of primarily cornflour, has the same properties. Corn starch is used as a thickening agent in soups and liquid-based foods, such as sauces, gravies and custards by mixing it with a cold liquid to form a paste or slurry. It is sometimes preferred over flour because it forms a translucent mixture, rather than an opaque one. As the starch is heated, the molecular chains unravel, allowing them to collide with other starch chains to form a mesh, thickening the liquid (Starch gelatinization). It is usually included as an anticaking agent in powdered sugar. Baby powder often uses cornstarch. Corn starch when mixed with a fluid can make a non-Newtonian fluid, e.g. adding water makes Oobleck and adding oil makes an Electrorheological fluid.

Normal, Newtonian liquids, like water, stay the same viscosity no matter what force is applied. But non-Newtonian liquids, like tomato ketchup, change character under stress. Tomato ketchup stays almost solid in the bottom of a plastic bottle until it is squeezed, at which point it drenches your hotdog in sweet goo. In the language of physicists, it is 'shear thinning'. Tomato ketchup is a pseudoplastic or "shear thinning" substance which can make it difficult to pour from a glass bottle. Often, the neck of the bottle will appear to be blocked. A common method to getting ketchup out of the bottle involves inverting the bottle and shaking it or hitting the bottom with the heel of the hand, which causes the ketchup to flow rapidly. A technique known widely among caterers involves inverting the bottle and forcefully tapping its upper neck with two fingers. Specifically, with a Heinz ketchup bottle, one taps the 57 circle on the neck. This helps the ketchup flow by applying the correct shearing force. These techniques work because of how pseudoplastic fluids behave: their viscosity decreases with increasing shear rate. The faster the ketchup is sheared, the more fluid it becomes. After the shear is removed the ketchup thickens to its original viscosity KETCHUP

Scientists had believed that the peculiar non-Newtonian behaviour of some liquids had been caused by particles moving in layers, like cars moving on a motorway. In the case of ketchup, they theorised, the application of force led to a streamlining of particles' trajectories, leading to fewer collisions and easier flow. Using a confocal microscope and a viscosity meter the researchers watched the flow of silica spheres suspended in a mixture of water and glycerine as it transitioned from thinning to Newtonian and, finally thickening behaviour. From their observations, the Cornell team concluded the amount of layering does not change the liquids enough to be the cause of so-called non-Newtonian behaviour. Instead, they now believe, shear thinning happens when the stress overrides the thermally induced 'Brownian motion' that would otherwise make particles randomly disperse. Conversely, they concluded, shear thickening happens when the particles move too quickly past each other for the fluid to get out of the way, causing particles to lock together and form clumps making the fluid more viscous. KETCHUP... KETCHUP... KETCHUP...

Silly Putty is a toy based on silicone polymers which displays unusual physical properties. It bounces, but breaks when given a sharp blow and can also flow like a liquid. It contains a viscoelastic liquid silicone, a type of Non-Newtonian fluid, which makes it act as a viscous liquid over a long time period but as an elastic solid over a short time period. Its viscosity depends on both temperature and on the force applied to it. Unlike corn starch solution, however, Silly Putty's solid nature resembles rubber, not rock. That's because its main ingredient is polydimethylsiloxane, a material with viscoelastic properties. In other words, over long flow times or at high temperatures, Silly Putty behaves like a highly viscous fluid. But over short flow times or at low temperatures, it behaves like an elastic solid.

Flubber is a non-Newtonian fluid, easily made from polyvinyl alcohol–based glues and borax, that flows under low stresses but breaks under higher stresses and pressures. This combination of fluid-like and solid-like properties makes it a Maxwell solid. Its behaviour can also be described as being viscoplastic or gelatino us.

In a large tub combine food colouring, glue and 1 and 1/2 cups of warm water In a smaller container, combine 1 and 1/3 cups warm water and Borax. Mix ingredients in each container thoroughly. Pour contents of smaller container into larger container. Gently lift and turn the mixture with a metal spoon until only about a tablespoon of liquid is left. INGREDIENTS 1 & 1/2 cups warm water 2 cups white glue 1 1/3 cups warm water 3 tsp Borax food colouring mixing bowl and spoon

Another example of this is chilled caramel ice cream topping (so long as it incorporates hydrocolloids such as carrageenan and gellan gum). The sudden application of force for example by stabbing the surface with a finger, or rapidly inverting the container holding it leads to the fluid behaving like a solid rather than a liquid. This is the "shear thickening" property of this non-Newtonian fluid. More gentle treatment, such as slowly inserting a spoon, will leave it in its liquid state. Trying to jerk the spoon back out again, however, will trigger the return of the temporary solid state.

CUSTAR D Cooked custard is a weak gel, viscous and thixotropic while it does become easier to stir the more it is manipulated, it does not, unlike many other thixotropic liquids, recover its lost viscosity over time. A suspension of uncooked imitation custard powder (starch) in water, with the proper proportions, has the opposite rheological property: it is negative thixotropic, or dilatant, allowing the demonstration of "walking on custard" see the physical properties of custard powder

BIBLIOGRAPHY ketchup-squirts-Scientists-uncover-mystery-non-Newtonian- liquids.htmlhttp:// ketchup-squirts-Scientists-uncover-mystery-non-Newtonian- liquids.html Liquids/Oobleck-versus-flubber ian_Fluid_with_Standards.pdf ian_Fluid_with_Standards.pdf

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