Page 31 - General_Knowledge_7
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Enlighten Me!
Why is it hard for Ketchup to flow?
When you overturn a sauce bottle that has been left untouched for
some time, chances are, that either the sauce will not come out at all or
a gigantic blob will plop down on your plate. Getting ketchup to ‘flow’
out of the bottle can be quite an ordeal.
However, if you shake the bottle before overturning it, the thick gooey
ketchup will flow out more freely.
Why does this happen?
This strange property of changing from gel like thickness (half liquid-
half solid, like your toothpaste) to free flowing liquid and back again
is called Thixotropy . So, ketchup is a semi-liquid substance which
changes state on being handled. This happens because of the shape of
the ketchup molecules. They are in the form of long chains. When the
ketchup bottle is left untouched for some time, the molecule chains coil
up together in a jumble. When the bottle is shaken, the molecules break
apart and become loose. Hence, the ketchup starts flowing.
You can even make your own thixotropic
substance! For that, you will need one cup
of cold water and one and a half cups of
cornstarch. Now, pour the water into a
shallow dish. Add the cornstarch to the
water slowly, one teaspoon at a time, and
stirring all the while. Continue till you
have exhausted all the cornstarch. Strike
the surface of the water-cornstarch mixture
with the back of a spoon. The mixture will
not splatter like any other liquid. This is true
for any thixotropic mixture.
If you drop a small hard object, such as a tennis ball, on its surface, the mixture becomes firm and does
not splash. This is because cornstarch and water molecules have fairly fixed positions. They cannot
move freely under pressure and behave more like a solid. However, if there is no pressure, the mixture
behaves like a liquid.
Quicksand is also a thixotropic mixture, wherein the more the pressure you apply, the harder it gets to
free yourself. The best way of getting out of quicksand is to apply force very slowly. Similarly, the best
way to make the ketchup flow out of the bottle is to insert a straw in the bottle, right up to the bottom.
It will allow the vaccum to full up with air. This will make the ketchup flow easily.
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