What is Viscosity?
The viscosity is a measure of the resistance of a fluid to flow. It defines the friction within a moving fluid. A fluid with large viscosity resists motion because it gives it a lot of internal friction due to its molecular structure. A fluid with low viscosity flows easily because when it is in motion, its molecular structure results in very little friction. For example, let’s take a funnel. Water flows very fast through a pipe, as it has very little flow resistance or very little viscosity. That is to say, it's not very thick. On the other hand, it may take a little longer to run honey through a funnel. This is because it has greater flow resistance, more viscosity, and is thicker in nature.
What is the Coefficient of Viscosity?
The quantitative value of the viscosity i.e degree to which a fluid resists flowing under an applied force is called the coefficient of viscosity. There are two types of coefficient of viscosity.
Dynamic Viscosity: Dynamic viscosity(η) normally called viscosity is the ratio between the shearing stress (F/A) to the velocity gradient \[(dv_{x}/dz)\] in a fluid.
\[\eta = \frac{\frac{F}{A}}{\frac{dv_{x}}{dz}}\]
A common form of this equation is known as Newton's equation which says the resulting shear of a fluid is directly proportional to the force applied and inversely proportional to its viscosity.
\[\frac{F}{A} = \eta \left ( \frac{dv_{x}}{dz} \right ) \Leftrightarrow F = \frac{mdv}{dt}\]
The SI unit of dynamic viscosity is pascal second and the common unit: dyne second per square centimeter(\[dyne - s/m^{2}\]).
Kinematic viscosity: Kinematic viscosity(ν) is the ratio between the viscosity of a fluid to its density. Kinematic viscosity is a measure of a fluid's resistive flux under gravity influence.
\[V = \frac{\eta }{\rho}\]
Units: SI unit: square meter per second (\[m^{2}/s\]). Common unit: square centimeter per second (\[cm^{2}/s\]).
Factors Affecting Viscosity
Temperature: Temperature is one of the key factors influencing viscosity. When the temperature decreases, viscosity gets higher.
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Chemical Composition: The viscosity of liquids generally depends on their molecule’s size, shape, and chemical nature. It is greater with smaller molecules than with larger; with elongated molecules than with spherical ones. Normally large quantities of dissolved solids increase the viscosity.
Colloid Systems: The lyophilic colloid solution has typically a fairly high viscosity
Suspended Material: Suspended particles cause the viscosity to increase.
Viscosity Experiment to Determine the Coefficient of Viscosity
Aim:
Determine the viscosity coefficient of a given viscous liquid by measuring the terminal velocity of a given spherical organism (by Stokes method).
Material Required:
A half-meter high transparent viscous liquid, one steel ball 5 cm broad glass cylindrical jar with millimeter graduations along with its height, screw gauge, clamp withstand, stop clock/watch, thermometer.
Theory
Terminal velocity: Terminal velocity is the maximum velocity attained by the object falling through a fluid. The acceleration of the object becomes zero when the summation of drag force and buoyancy equals the gravity, this makes the acceleration zero.
The formula for the terminal velocity:
\[V = \frac{2r^{2}(\rho - \sigma )g}{9 \eta} \]
Where,
v-terminal velocity
r-radius of the spherical body
g-acceleration due to gravity
ρ-density of the spherical body
σ-density of the liquid
η-coefficient of viscosity
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Knowing ρ, σ, r, and calculating v, we can find the coefficient of the viscosity.
Procedure:
Clean the glass jar, and fill it with transparent viscous liquid.
Verify that the vertical scale is clearly visible along with the height of the jar. Note its slightest count.
Test the tight spring stopwatch. Find the least count and (if any) zero error.
Find and note the screw gauge's least count and zero error.
Determine the mean ball radius.
Drop the ball in the liquid, gently. It falls down with accelerated velocity in the liquid for about one-third of the liquid's height. Then, uniform terminal velocity falls.
When the ball hits a suitable division (20 cm; 25 cm; ..........) start the stopwatch. Note its downfall.
Just when the ball hits the lowest convenient division (45 cm), stop the stopwatch.
Find and note the falling distance and the time the ball has taken.
Repeat steps 6 to 9 more than two times.
Note, and record the liquid temperature.
Record your remarks as given ahead here.
Observations:
Least count of vertical scale = 1 mm
Least count of stopwatch = …….. s
Zero error of stopwatch = ……. s
Pitch of screw gauge (p) = 1mm
No.of divisions on the circular scale = 100
Least count of the screw gauge (LC) = 1/100 = 0.01 mm
Zero error of the screw gauge (e) = …… mm
Zero correction of the screw gauge (c) =….. Mm
For the diameter of the spherical ball:
Along one direction, \[D_{1}\] = ….. mm
In the perpendicular direction, \[D_{2}\] = …….. Mm
For the terminal velocity of the spherical ball
Distance fallen, S = …… cm
Time took,
\[t_{1}\] = …….. S
\[t_{2}\] = …….. S
\[t_{3}\] = …….. S
Result
The coefficient of viscosity of the liquid at a temperature (T℃) is ______
Note
In gases, the viscosity coefficient increases with an increase in the temperature.
In the case of the liquid, the coefficient of viscosity decreases with an increase in the temperature.
Types of Viscosity
Dynamic viscosity is defined as the tangential force per unit area necessary to move a fluid in one horizontal plane with respect to another plane at a velocity of unit value while the fluid's molecules retain a unit distance apart.
Kinematic Viscosity
Kinematic viscosity is a type of viscosity calculated by dividing the fluid mass density by the dynamic fluid, viscosity, or absolute fluid viscosity. It's also known as momentum diffusivity from time to time. Kinematic viscosity is measured in terms of time and fluid area. When no external force is applied except gravity, kinematic viscosity is the measurement of a fluid's inherent resistance to flow. This is a force-independent quantity that is the ratio of dynamic viscosity to density. The kinematic viscosity of a fluid may be calculated by dividing its absolute viscosity by its mass density.
Application of Viscosity
The distinctive attribute of a liquid is viscosity, which is undifferentiated from the frictional force. The following are a few of the numerous applications of viscosity:
High-thickness liquids are used in painting.
Viscosity is considered while arranging food items such as dosas and chapatis.
Pen ink is made up of liquids with a high viscosity.
Paints, varnishes, and similar home items have their viscosity carefully controlled so that they may be applied easily and uniformly with a brush roller.
Gum is made up of very sticky substances that cling to objects inexorably.
The thickness of family unit items like paints and stains is directed in such a way that applying paint over the brush is straightforward.
The viscosity of fluids affects blood circulation in arteries and veins.
The oil drop experiment was used by Millikan to calculate the charge of an electron. He calculated the charge using his understanding of viscosity.
Brake fluid transmits force via the braking system, and if it had a different viscosity, it would not function correctly.
FAQs on To Determine the Coefficient of Viscosity of a Given Viscous Liquid
1. Why is Viscosity important in daily life?
Lubrication in Vehicle- When you put oil in your vehicle, keep the viscosity in mind. This is due to the fact that viscosity affects friction, and friction, in turn, influences heat. The pace of oil consumption and the ease with which your car will start in hot or cold circumstances are also affected by viscosity. If your oil has a low viscosity index, it may become thinner as it heats, which might cause difficulties while driving your automobile on a hot summer day.
Cooking- Viscosity is an important factor in food preparation and serving. When fats are cooled, they become solid. When fats are heated, they become fairly viscous. The viscosity of sauces, soups, and stews is also important in different cuisines.
Manufacturing- To function properly, manufacturing equipment needs the use of suitable lubricant. Too viscous lubricants can block and choke pipes. Lubricants that are excessively thin offer insufficient protection for moving components.
Medicines- Viscosity is important in medicine since fluids are injected into the body intravenously. Blood viscosity is a critical issue: overly viscous blood can create deadly internal clots, while too thin blood will not clot, resulting in catastrophic blood loss and possibly death.
2. What are the types of Viscosity?
There are two types of viscosity dynamic viscosity and kinematic viscosity. Each depicts the movement of fluid in a unique way. When the density of the liquid is known, they are compatible.
Dynamic Viscosity- The dynamic viscosity of a liquid is defined as the ratio of shear pressure to shear rate.
Kinematic Viscosity- A liquid's kinematic viscosity is the ratio of gooey force to inward force. Kinematic viscosity is analogous to the dispersion of mass and heat.
3. Where can I find Chemistry Learning Resources to prepare for my exams?
Students may find and access Chemistry Learning Resources on Vedantu. They may readily download sets of these learning tools in PDF format to help them recall during revision. Students can use these Sample Papers to assess their strong and weak areas in every subject. They gain a thorough comprehension of the various ideas as well as how the exam questions are asked. These learning resources also help students revise concepts, gain confidence, and develop step-by-step response writing abilities before the test.
4. Why does liquid need to be transparent and how does the viscosity of liquid and gases change?
The liquid needs to be transparent in order to watch the movement of the ball in the liquid. When the temperature rises, the liquid's viscosity decreases, and the gas's viscosity increases with the temperature increase. When the pressure decreases, the liquid's viscosity decreases, and the gas's viscosity is not affected.
5. Differentiate the dynamic and kinematic viscosity?
Dynamic viscosity is fluid flow resistant. It gives a glimpse of fluid thickness. If the fluid is as thin as water, it will have less viscosity. Whereas kinematic viscosity is the relation between the viscous force of the fluid and the inertial force. Dynamic viscosity is also called absolute viscosity or just viscosity whereas kinematic viscosity is also called momentum diffusivity.
