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.