UNIT 2/EAT Good Enough to Eat

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UNIT 2/EATGood Enough to Eat
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In this topic we look at

• Fluid flow (VISCOSITY)
• Material properties
• Refraction sugar content of liquids
  (REFRACTOMETRY)
• POLARISATION of light
• in the context of food (especially sweets!)

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(No Transcript)
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We can say that viscosity is the resistance a
material has to flowing (or changing form). It
affects the speed at which a fluid flows a
viscous liquid is more runny. This property can
be thought of as an internal friction. We can
compare viscosities with a viscometer, but to
measure it we use the falling ball test (see
later).
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When a fluids moves slowly, its flow is orderly
and we call it LAMINAR FLOW, represented by
STREAMLINES
Streamlines close to the sides of the edge of the
flow will indicate slower velocity, as there is
more friction with the sides. The fastest flow is
in the centre.
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Fast moving fluids do not flow orderly the
streamlines become chaotic unstable, producing
TURBULENT FLOW. Layers move past each other
creating friction, and this increases if a liquid
is more viscous. The flow forms loops, whirls and
eddies, wasting energy, causing more drag and
heating the fluid up
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• Designers of cars or submarines want air or
  water to flow past them in laminar flow, to
  reduce drag and save energy.
• Chocolate flow in factories needs to be laminar
  to prevent uneven coating and formation of air
  bubbles.
• Oil flowing in pipes across hundreds of miles of
  Saudi Arabia would heat up if it did not have
  laminar flow.

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Viscosity is affected by temperature DATA FOR
WATER
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Engine lubrication Car engines use oil to
prevent friction, but as the car engine heats up
during use, the oil viscosity will change. An
ideal oil at cold temperatures would be too runny
when hot to lubricate properly. The solution is
to design a special lubricant with additives that
prevent the viscosity changing with temperature.

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STOKES LAW When a spherical object, moves
through a viscous liquid there is a viscous drag
force upon it Fdrag 6?r?? where r radius
of sphere, ? viscosity and ? velocity of
sphere.
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We can therefore find this viscosity by dropping
a sphere in a fluid, and measuring its terminal
velocity. At this point Weight (downwards)
Viscous Drag Upthrust (upwards) Since the
Upthrust on sphere weight of fluid displaced
(Archimedes Principle) Msphereg 6?r??
Mfluidg (in practice, we would say Mass
Density x Volume)