Post on 13-Sep-2019
TERM HOMEWORK PHYSICS VISCOSITY
Kaan Erdibil 9/C
PARAMETERS THAT AFFECT VISCOSITY
Kaan Erdibil 9/C
Index
Research question ……………………………1
Introduction ……………………………………..2
Materials and Methods ……………………..3
Table ………………………………………………….4
Dıscussion …………………………………………..5
Factors effecting viscosity……………………6,7
Experiment ……………………………8,9,10,11,12
Conclusion ………………………………………………13
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RESEARCH QUESTION
How does temperature, pressure and molecular structure of a
substance affects viscosity?
Temperature
A liquids viscosity strongly depends on its temperature. Along with
the shear rate, temperature really is one of the biggest factors. The
higher the temperature is, the lower a substance's viscosity is.
Consequently, decreasing temperature causes an increase in viscosity.
The relationship between temperature and viscosity is inversely
proportional for all substances. A change in temperature always
affects the viscosity. For some fluids, a decrease of 1°C already causes
a 10 % increase in viscosity.
Pressure
In most cases, a fluid's viscosity increases with increasing pressure.
Compared to the temperature influence, liquids are influenced very
little by the applied pressure. The reason is that liquids (other than
gases) are almost non-compressible at low or medium pressures. For
most liquids, a considerable change in pressure from 0.1 to 30 MPa
causes about the same change in viscosity as a temperature change of
about 1 K (1°C).
-1-
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İntroduction
In our planet, there are 4 forms of matters that we can observe.
One of them, which is the most important for me, is liquid matters. A
liquid is a sample of matter that conforms to the shape of a container
in which it is held, and which acquires a defined surface in the
presence of gravity. Viscosity is a characteristic quality of liquids and
gasses. Gases also have a viscosity, although it is a little harder to
notice it in ordinary circumstances. Viscosity is a measure of a fluid's
resistance to flow. It describes the internal friction of a moving fluid. (
"What Is Viscosity?" Web.)
This workshop here we will not discuss the rates of flow, nor
the coefficients for calculation but the principles of the matter to
extract the idea why a fluid’s flow rate changes and the variables that
affect it.
A fluid with large viscosity stands against the motion and flow
because its molecular makeup gives it a lot of internal friction. A fluid
with low viscosity flows easily because its molecular makeup results
in very little friction when it is in motion. So shortly viscosity is the
quantity that describes a fluid's resistance to flow. We can observe
viscosity of the objects very easily in daily life. For example, the
honey you eat on every breakfast. Take a spoon of honey and try to
release it really quickly. It won't drop very easily , it will resist
motion. However, it will start to flow slowly at some point. After that
try it with another liquid. For example, let's take milk. Have a glass of
milk and empty it to the other glass. All the milk will pass through in a
second or two. That is because of the viscosity of honey is more than
the milk.( "Vıscosity." The Physics Hyper Textbook. Ed. Glenn Elert.
The Physics Hyper Textbook. Web. )
Materials and Methods Erdibil 3
Viscosity of the liquids must be observed in two distinctive
series, first one is simple liquids such as water, alcohol, liquid oil,
mercury, which are also called the newtoinian fluids and the second
series however pastes, gels, emulsions, like butter, or toothpaste being
also called as non-newtonian fluid in which the viscosity is a function
of some mechanical variable like shear stress or time.( Shear stress=
viscosity x shear rate )
Formally, viscosity (represented by the symbol η "eta") is the ratio of
the shearing stress (ƒ/A) to the velocity gradient (Δvx/Δz or dvx/dz)
in a fluid.
η = F̅/A
Δvx/Δz
The more common way to show this relationship is called “Newton’s
equation”,
says that the resulting shear of a liquid is directly proportional to the
force
applied and inversely proportional to its viscosity.
It is very similar to Newton’s second law of motion.( F= ma)
F = η
dvx
A dz
⇔ F = m dv
dt
("Vıscosity." The Physics Hyper Textbook. Ed. Glenn Elert. The
Physics Hyper Textbook. Web. )
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Table showing viscosities of some matters….
simple liquids T (C) η (mPa s) gases T (℃) η (μPa s)
alcohol, ethyl
(grain) 20 1.1 air 15 17.9
alcohol, isopropyl 20 2.4 hydrogen 0 8.42
alcohol, methyl
(wood) 20 0.59 helium (gas) 0 18.6
Blood 37 3–4 nitrogen 0 16.7
ethylene glycol 25 16.1 oxygen 0 18.1
Honey 20 10
There are actually two quantities that are called viscosity. The
quantity called dynamic viscosity, absolute viscosity, or simple
viscosity to distinguish it from the other quantity, but is usually just
called viscosity. The other quantity called kinematic
viscosity(represented by the Greek letter ν "nu") is the ratio of the
viscosity of a fluid to its density.
ν = η
ρ
Discussion Erdibil 5
All liquids have their own viscosity. It depends on their
intermolecular force and also density. Water which has the density 1
has less viscosity than mercury which has the density of 13.534
g/cm3. Because mercury has more density, its molecules want to stay
together so it makes the flow rate slower which we call more viscous.
On the other hand, water molecules also want to stay together but the
forces that keep the molecules together are less than mercury. So
water is less viscous. From this example, we can predict that viscosity
of a liquid is directly proportional to its density. If density increases,
viscosity will increase too and if density decreases viscosity will
decrease too.
IMPORTANT NOTE:
This experimental study takes in to account the specialities of regural
liquids. Therefor, not all conclusions would apply as expected on
irregular fluids such as; uhu, adhesives which solidify at certain
temperature or plastics and even organic substances such as milk
which are subject to losing it’s chemical form by temperature and
transforming it’s specialities.
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Factors Affecting Viscosity
The Density of liquids has a big role affecting the viscosity. But the
compound of the liquid which is the molecular interactions , cohesion,
and adhesion, at a given temperature and pressure will also have a big
effect on viscosity. Such as; liquid oils would float on water which
shows they have a lower density than the water, on the other hand
while flowing in a tube, oil would be much more viscous. Just as the
same, honey and the adherents,such as Uhu, Bally, because of their
chemical compound would have less density but more viscosity.
Therefore, simple liquids must be separately examined than adherent
compounds, mentioned above, such as uhu, bally, or mustard,
ketchup, honey, peanut butter. Solutions according to their chemical
compounds could also increase and decrease viscosity. They would
increase viscosity by increasing its density while they could affect the
freezing point so changing the effect of temperature and decrease the
viscosity.Just like see water being more viscous than püre water
would freeze in lower temperature than a pure water lake thus while
increasing viscosity normally, could have a decreasing effect by
changing the liquids behaviours due to changes in the temperature.
When you have just taken your honey pot out of the refrigerator,
pour it on your plate. You will see that it flows very slowly. İf it waits
in the room temperature 21 degrees Celcius, you will see that it pours
much easily than before. This is one of the most simple examples
showing the rise in the temperature decreases viscosity and increasing
the flow rate; while decreasing the temperature would increase the
viscosity. Engine oil and hydraulic fluids thicken appreciably on cold
days and affect the performance of cars and other vehicles during the
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winter months. Generally, the viscosity of a simple liquid decreases
with increasing temperature (and vice versa). As temperature
increases, the average speed of the molecules in liquid increases and
the amount of time they spend "in contact" with their nearest
neighbors decreases. Thus, as temperature increases, the average
intermolecular forces decrease. The exact manner in which the two
quantities vary is nonlinear and changes abruptly when the liquid
changes phase.( "Factors Affecting Viscosity." Viscopedia. Web. )
Factors Affecting Viscosity
• Viscosity is a characteristic of materials. (Viscosity is a property
of materials.)
• The viscosity of simple fluids…
decreases with increasing temperature
increases under very high pressures.
EXPERIMENT Erdibil 8
Independent variable: Temperature
Dependent variable: Viscosity of honey
Constant variables : pressure, see level, type
of honey…
I did an experiment which aims to show the effect of temperature and
pressure on honey. I observed the viscosity of honey first at winter (8-
10Celcius) and calculate the time that it dropped from the spoon to
ground. I did the same thing after 4 months at spring (25-27 Celcius).
I didn't use the fridge or microwave to change the environment
because this way ı could observe better and see the change by natural
effects. When ı drop the honey from the spoon to the ground, at
winter, it took 9 seconds to the first drop to fall. At spring from the
same height, it took 5 seconds. So ı observed the change in the
viscosity of honey by temperature. As temperature increases the
viscosity decreases because of the intermolecular forces decreases.
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EXPERIMENT 2
Independent Variable: Types of liquid
Dependent Variable: The time that liquid pour
in the glass
Constant Variable: injecktors(5cc), tubes(3mm
dia.),room temperature etc.
To compare 3 different liquids viscosity, we
prepeared our experiment with 15 cm tubes
and consequently water, oil, liquid soap. Than
we measured the time for 5cc liquid pass
through the tube.
WATER OIL LIQ. SOAP Flow time 2.30 sec 4.30 sec 11.00 sec Flow rate 6 cm/s 3.33 cm/s 1.36 cm/s
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Water appeared to be the least viscous liquid
with highest flow rate as expected. Oil is more
viscous than water roughly 2 times viscous.
Liquid water was measured to be the most
viscous liquid in our experiment with flow
time 4 times compared to water. Interestingly
water which is the most homogenous liquid
having the highest flow rate and least
viscosity, followed by the oil chemically more
heterogenous and the liquid soap, the most
viscous, being the most complex chemical
compound indicating roughly how chemical
constitutation affects viscosity.
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Conclusion
Viscosity is a quantity which gasses and liquids
have and measures the resistance to flow.
Larger viscosity a fluid have, more internal
friction it has and more force to stand against
the motion. A liquid which has less viscosity
has less internal friction and also less force to
stand against the motion. To sum up, the
viscosity is the quantity that describes a fluids
resistance to flow. And we can observe it
anywhere in daily life.