viscosity experiment sphere

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Experimental determination of viscosity (viscometer)

Viscometry is the experimental determination of the viscosity of liquids and gases with so-called viscometers.

Definition of viscosity (Newton’s law of fluid friction)

Viscosity describes the internal resistance to flow of a fluid (internal friction). It is defined by the shear stress τ required to shift two plates moving relative to each other. The higher the relative velocity Δv of the plates and the smaller the distance Δy between the plates, the greater the shear stress. The proportionality constant between these quantities is the (dynamic) viscosity η. This law is also known as Newton’s law of fluid friction:

\begin{align} \label{t} &\boxed{\tau= \eta \cdot \frac{\Delta v}{\Delta y}} ~~~&&\text{Newton’s law of fluid friction}\\[5px] &{\tau=\frac{F}{A}} ~~~&&\text{ shear stress} \\[5px] \end{align}

More detailed information on viscosity and Newton’s law of fluid friction can be found in the article Viscosity .

Rotational viscometer

The confinement of a fluid between two plates to define the viscosity is a very descriptive procedure, but is hardly feasible in practice. How should the fluid be held within the gap between two plates? In practice, therefore, a spindle is used which rotates at a constant speed in a cylindrical vessel. The vessel contains the fluid whose viscosity is to be determined. Such an apparatus for determining the viscosity is also called a rotational viscometer .

Depending on the viscosity, the drive of the spindle requires a certain torque. The higher the viscosity, the greater the torque required to keep the rotational speed constant. This torque is measured directly at the motor and can be used to determine the viscosity after an appropriate calibration. However, the rotational speed must not be selected too high, because at too high speeds no laminar flow is developed but a turbulent flow .

Falling sphere viscometer

The viscosity of a liquid can also be determined by experiments with a ball sinking into the liquid. The speed at which a ball sinks to the ground in a fluid is directly dependent on the viscosity of the fluid. The fluids used are mainly liquids.

The physicist George Gabriel Stokes derived the following equation, which shows the relationship between the speed v at which a sphere of radius r is drawn through a fluid of viscosity η and the resulting frictional force F f :

\begin{align} \label{s} &\boxed{F_f = 6\pi \cdot r \cdot \eta \cdot v} ~~~\text{Stokes’ law of friction} \\[5px] \end{align}

Note that Stoke’s law only applies to spherical bodies that are laminar flowed around!

If a ball is dropped in a viscous liquid, the speed increases at first until the opposing frictional force is as great as the weight force of the ball. For more accurate measurements, the upward buoyant force must also be taken into account. All three forces balance each other in the steady case and a constant sinking speed is obtained:

\begin{align} \label{gg} &F_g \overset{!}{=} F_f + F_b \\[5px] \end{align}

The weight force F g of the ball can be determined via the volume V b and the density of the ball ϱ b :

\begin{align} \label{g} &F_g = m_b \cdot g = V_b \cdot \rho_b \cdot g= \frac{4}{3}\pi r^3 \cdot \rho_b \cdot g\\[5px] \end{align}

The buoyant force F b is determined on the basis of the Archimedes’ principle from the weight force of the displaced liquid, whereby the displaced volume corresponds exactly to the volume of the ball:

\begin{align} \label{a} &F_b = m_f \cdot g = V_b \cdot \rho_f \cdot g= \frac{4}{3}\pi r^3 \cdot \rho_f \cdot g \\[5px] \end{align}

If one now uses the equations (\ref{s}), (\ref{g}) and (\ref{a}) and put them into equation (\ref{gg}), then the viscosity η of the liquid can be determined from its sinking speed v s :

\begin{align} &F_g \overset{!}{=} F_f + F_b \\[5px] &\frac{4}{3}\pi r^3 \cdot \rho_b \cdot g = 6\pi \cdot r \cdot \eta \cdot v_\text{s} + \frac{4}{3}\pi r^3 \cdot \rho_f \cdot g \\[5px] &6\pi \cdot r \cdot \eta \cdot v_\text{s} = \frac{4}{3}\pi r^3 \cdot \rho_b \cdot g ~- \frac{4}{3}\pi r^3 \cdot \rho_f \cdot g \\[5px] &6\pi \cdot r \cdot \eta \cdot v_\text{s} = \frac{4}{3}\pi r^3 g \left(\rho_b-\rho_f\right) \\[5px] \label{e} &\boxed{\eta = \frac{2r^2g}{9~ v_\text{s}}\left(\rho_b-\rho_f\right) } ~~~~~r \ll R\\[5px] \end{align}

When performing the experiment, however, the sink rate must not be too high. On the one hand, because then it cannot be ensured that a state of equilibrium has been reached before the ball hits the ground. On the other hand, a laminar flow around the ball must always be assured, which is not the case at high speeds, as turbulence is then created.

Furthermore, the radius R of the cylindrical tube should be large compared to the radius r of the ball falling within it, otherwise there will be flow effects between the ball and the tube wall that can no longer be neglected. This results in additional friction of the liquid flowing past and a reduction in the sinking speed of the ball (principle of hydraulic damping). Due to the finite radius of the tube, the sinking speed of the ball is therefore always measured too small in practice. Therefore, the sinking velocity is corrected with an empirical correction factor L (called Ladenburg factor ):

\begin{align} \label{h} &\boxed{\eta = \frac{2r^2g}{9 ~v_\text{s} \cdot L}\left(\rho_b-\rho_f\right) } ~~~\text{where}~~~ \boxed{L=1+2.1 \frac{r}{R}}>1 \\[5px] \end{align}

In practice, the correction factor is usually determined in advance of the test using a liquid of known viscosity.

Falling sphere viscometer by Höppler

The falling ball viscometer by Höppler is based on the falling sphere method described in the previous section. A ball falls to the ground in a tube which contains the liquid to be examined. Two markings are attached to the tube which indicate a defined measuring distance Δs (“falling distance”). The time Δt required for the ball to pass through this measuring distance is measured by means of light barriers. The speed of descent v s of the sphere is therefore given by the following formula:

\begin{align} & v_\text{s} = \frac{\Delta s}{\Delta t}\\[5px] \end{align}

If the formula for the rate of descent is used in equation (\ref{h}), the viscosity η of the liquid can be determined with the following formula:

\begin{align} &\eta = \underbrace{\color{red}{\frac{2r^2g}{9 \cdot \Delta s \cdot L}}}_{\text{constant}~ \color{red}{C}} \cdot \left(\rho_b-\rho_f\right) \cdot \Delta t\\[5px] \label{eta} &\boxed{\eta = C \cdot \left(\rho_b-\rho_f\right) \cdot \Delta t } \\[5px]\\[5px] \end{align}

The term marked in red is a specific constant of the measuring apparatus, which also depends on the test sphere used. Depending on the viscosity to be expected, the manufacturers of Höppler viscometers provide various balls for which the test constant C has been determined in advance.

This constant also takes into account that the tube is not exactly vertical, but inclined. Therefore the ball sinks not only by falling, but also by rolling. This rolling motion guides the test ball stably downwards. In this way, turbulence in the liquid is avoided and the validity of Stokes’ Law is ensured, i.e. in particular the proportionality between frictional force and sinking speed. In the case of turbulent flow, the frictional force would no longer be proportional to the sinking speed and the viscosity would no longer be a linear function of the duration of the fall – equation (\ref{eta}) would no longer be valid.

In order to study the temperature influence on the viscosity, the tube is usually placed in another tube filled with water. Circulating thermostats can be used to precisely control the temperature of the water bath and thus the liquid to be examined.

Capillary viscometer by Ubbelohde

The capillary viscometer is based on the Hagen-Poiseuille law for pipe flows. This law states that the volumetric flow rate V* through a capillary is dependent on the viscosity η of the liquid flowing through (assumed that the flow is fully developed):

\begin{align} &\boxed{\dot V = – \frac{\pi R^4}{8 l \eta}\Delta p } \\[5px] \end{align}

In this equation, R denotes the radius of the capillary and l its length. The pressure difference Δp corresponds to the pressure drop between the beginning and end of the capillary, which ultimately causes the flow of the liquid. Below the capillary is an L-shaped tube so that the same ambient pressure applies above and below the capillary. Thus the liquid is driven only by the hydrostatic pressure . The pressure drop Δp is thus dependent on the density of the liquid.

The volumetric flow rate through the capillary can be determined by measuring time and mass that has flowed through. However, manufacturers of capillary viscometers usually summarize the device-dependent variables such as radius and length of the capillary in a constant C. Thus, only the time period t has to be determined within which the liquid in the reservoir has passed two marks. In addition, the density of the fluid ϱ f is required, since this determines the pressure drop in the Hagen-Poiseuille law. With the following formula the viscosity η can then be determined:

\begin{align} &\boxed{\eta= C \cdot \rho_f \cdot (t-t_c)} \\[5px] \end{align}

As already mentioned, the Hagen-Poiseuille law only applies to a fully developed flow. At transition from reservoir to capillary (and up to some degree also within the capillary) however, the flow is not yet fully developed, but is accelerated. The energy required to accelerate the fluid means an additional pressure drop. To take this into account, the measured time is therefore corrected by a so-called Hagenbach correction time t c .

Dip cup viscometer

A very simple method for determining viscosity is the dip cup viscometer . This method makes use of the fact that the discharge of a liquid through a hole in a vessel also depends on the viscosity. Due to the high flow resistance, highly viscous liquids take a relatively long time to flow out through a hole in the dip cup . For a given cup volume, the time required to discharge the liquid is therefore a direct measure of viscosity.

Manufacturers of dip cups list the corresponding viscosity in their data sheets depending on the discharge time. Depending on the viscosity to be expected, different dip cups are to be used. In order to obtain valid results, the discharge time must also be within a certain range. If this is not the case, another dip cup must be used.

The dip cup viscosimeter is mainly used to determine the viscosity of paints or lacquers. These liquids would otherwise heavily contaminate conventional viscometers. Furthermore, very fast results are obtained with a dip cup viscometer, so that paints or lacquers can be checked and further processed immediately after mixing.

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Core Practical 4: Investigating Viscosity ( Edexcel A Level Physics )

Revision note.

Core Practical 4: Investigating Viscosity of a Liquid

Aim of the experiment.

• By allowing small spherical objects of known weight to fall through a fluid until they reach terminal velocity, the viscosity of the fluid can be calculated
• Independent variable : weight of ball bearing, W s
• Dependent variable : terminal velocity, v term
• fluid being tested, 
• temperature

Equipment List

• Long measuring cylinder
• Viscous liquid to be tested (thin oil of known density or washing up liquid)
• Stand and clamp
• Rubber bands
• Steel ball bearings of different weights
• Digital scales
• Vernier calipers
• Digital stopwatch

• Weigh the balls, measure their radius using Vernier callipers and calculate their density
• Place three rubber bands around the tube. The highest should be far enough below the surface of the liquid to ensure the ball is travelling at terminal velocity when it reaches this band. The remaining two bands should be 10 – 15 cm apart so that time can be measured accurately
• If lap timing is not available, two stopwatches operated by different people should be used
• If the ball is still accelerating as it passes the markers, they need to be moved downwards until the ball has reached terminal velocity before passing the first mark
• Measure and record the distances d 1 (between the highest and middle rubber band) and d 2 between the highest and lowest bands.
• Repeat at least three times for balls of this diameter and three times for each different diameter
• Ball bearings are removed from the bottom of the tube using the magnet against the outside wall of the measuring cylinder

Table of Results:

• Terminal velocity is used in this investigation since at terminal velocity the forces in each direction are balanced
• W s = weight of the sphere
• F d = the drag force (N)
• U = upthrust (N)
• The weight of the sphere is found using volume, density and gravitational force
• v s = volume of the sphere (m 3 )
• ρ s = density of the sphere (kg m –3 )
• g = gravitational force (N kg −1 )
• Recall Stoke’s Law
• The volume of displaced fluid is the same as the volume of the sphere
• The weight of the fluid is found from volume, density and gravitational force as above
• Substitute equations 2, 3 and 4 into equation 1
• Rearrange to make viscosity the subject of the equation

Evaluating the Experiment

Systematic Errors :

• Ruler must be clamped vertically and close to the tube to avoid parallax errors in measurement
• Ball bearing must reach terminal velocity before the first marker

Random errors :

• Cylinder must have a large diameter compared to the ball bearing to avoid the possibility of turbulent flow
• Ball must fall in the centre of the tube to avoid pressure differences caused by being too close to the wall which will affect the velocity

Safety Considerations

• Measuring cylinders are not stable and should be clamped into position at the top and bottom
• Spillages will be slippery and must be cleaned up immediately
• Avoid getting fluids in the eyes

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curriculum for educators everywhere!

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• Measuring Viscosity

Hands-on Activity Measuring Viscosity

Grade Level: 9 (8-10)

Time Required: 1 hours 15 minutes

Expendable Cost/Group: US $1.00

Group Size: 3

Activity Dependency: Viscous Fluids

Subject Areas: Algebra, Biology, Chemistry, Measurement, Physical Science, Physics, Reasoning and Proof

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Engineers often design devices that transport fluids, use fluids for lubrication, or operate in environments that contain fluids. Thus, engineers must understand how fluids behave under various conditions. Understanding fluid behavior can help engineers to select the optimal fluids to operate in devices or to design devices that are able to successfully operate in environments that contain fluids.

After this activity, students should be able to:

• Measure the viscosity of a fluid.
• Describe a fluid as having "high" or "low" viscosity.

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Each group needs:

• graduated cylinder (the taller the better)
• marble or steel ball (must be half the diameter of the cylinder or smaller, and sink in the fluid being measured; the slower the ball sinks, the easier it is to measure the viscosity)
• Viscosity Activity Worksheet , one per person
• calculators
• Internet access, to research viscosities for one worksheet question

To share with the entire class:

• thick, somewhat clear household fluids, such as motor oil, corn syrup, pancake syrup, shampoo, liquid soap (perhaps a different fluid for each 1-2 groups), enough of each liquid to fill a graduated cylinder for each group that tests it
• scale, to measure the masses of graduated cylinders, with and without the liquids

Fluid mechanics is the study of how fluids react to forces. Fluid mechanics includes hydrodynamics, the study of force on liquids, and aerodynamics, the study of bodies moving through air. This encompasses a wide variety of applications. Can you think of any examples of engineering applications for which an understanding the behavior of fluids is important? (Listen to student ideas.) Environmental engineers use fluid mechanics to study pollution dispersion, forest fires, volcano behavior, weather patterns to aid in long-term weather forecasting, and oceanography. Mechanical engineers implement fluid mechanics when designing sports equipment such as golf balls, footballs, baseballs, road bikes and swimming gear. Bioengineers study medical conditions such as blood flow through an aneurysm. Aerospace engineers study gas turbines that launch space shuttles and civil engineers use fluid mechanics for dam design. Considering just these few examples of the wide variety of applications of fluid mechanics, you can see how fluid mechanics is important to understand for many types of engineering design in our world.

In this activity, we'll be measuring a property of fluids called viscosity. Viscosity describes how a fluid resists forces, or more specifically shear forces . Shear is the type of force that occurs when two objects slide parallel to one another. Since fluids are composed of many molecules that are all moving, these molecules exert a shear force on one another. Fluids with low viscosity have a low resistance to shear forces, and therefore the molecules flow quickly and are easy to move through. Can anyone name an example of a low-viscosity fluid? (Listen to student ideas.) One example is air! Another example is water. Fluids with high viscosity flow more slowly and are harder to move through. What are examples of high-viscosity fluids? (Listen to student ideas). One example of a high-viscosity fluid is honey.

Being able to re-arrange equations to find the unknowns is an important skill for engineers! In this activity, we will measure the viscosities of a few household fluids by dropping balls into them and measuring the terminal velocities.

Before the Activity

• Gather materials and make copies of the Viscosity Activity Worksheet .
• Be sure the ball sinks slowly enough in all of the fluids that a velocity measurement can be obtained. If the ball falls too quickly, it is hard to accurately start and stop the stopwatch.
• Divide the class into groups of three students each. Hand out the worksheets.

With the Students

• Have each group choose a fluid to measure the viscosity of (or assign each group a fluid).
• Have students calculate the density of the fluid.
• Weigh the empty graduated cylinder.
• Fill the cylinder with fluid, and record the volume.
• Weigh the full graduated cylinder. Subtract the mass of the empty graduated cylinder to determine the mass of the fluid.

Note: 1 cm 3 =1 ml.

• Have students measure the density of the sphere.
• Measure the radius of the ball. Record as r [cm].

Alternatively, place the sphere in a graduated cylinder half filled with water; the displacement of the water is equal to the volume of the sphere.

• Have students drop the ball into the fluid, timing the ball as it falls a measured distance.

(Note: Ideally students would wait for the ball to reach a constant velocity, however for this activity we assume the ball reaches terminal velocity very quickly, so that students can measure the time from when the ball enters the fluid until it reaches the cylinder bottom. For less-viscous, "thinner," fluids, this may be very quick).

where g is acceleration due to gravity (981 [cm/s 2 ]). The answer should be in units of kg/cm s, or mPa-s. For comparison, the viscosity of water is approximately 1 mPa-s.

• For accuracy, have students repeat the experiment and calculate an average viscosity.
• Have groups share, compare and discuss their results as a class by either writing the results in a table on the board or on a class overhead projector.

shear: A type of force that occurs when two objects slide parallel to one another.

terminal velocity: The point at which the force exerted by gravity on a falling object is equaled by a fluid's resistance to that force.

viscosity: A fluid's ability to resist forces.

Pre-Activity Assessment

Discussion Questions: Considering the fluids available for activity testing, ask students to estimate which liquid they think will have the highest viscosity. Which will have the lowest? Write their predictions on the board.

Activity Embedded Assessment

Worksheet : Have students complete the Viscosity Activity Worksheet during the activity. If time is limited, have them research online for viscosities of common household fluids (last question) as a homework assignment. Review their answers to gauge their comprehension of the subject matter.

Post-Activity Assessment

Graphing: Have students plot fluid density (independent) vs. viscosity (dependent). In addition, students could compare marbles of various diameters and describe patterns between fluid density and viscosity, and between fluid density and marble diamater. Students then determine if the model is linear, quadratic, or exponential; if linear, use the two-point method to determine the line of best fit.

Class Presentation: Have students share and discuss their measured/calculated viscosities with the class. Compare and discuss the class results with the predictions made before beginning the activity.

Safety Issues

• Do not allow students to drink the test fluids, especially after the fluids have been in contact with the graduated cylinders.
• After the activity, responsibly dispose of the used test fluids.
• Shampoo or dish soap may create a large amount of suds when cleaning the graduated cylinders.

If the marble falls too quickly through the fluid to obtain accurate timing, use a taller graduated cylinder or a lighter marble (or both!).

Viscosity changes with temperature! Have students measure the viscosity of a fluid at a few different temperatures and graph the viscosity (y-axis) vs. temperature (x-axis).

• For lower grades, just visually compare the times it takes the balls to fall through the fluids. Perhaps a viscosity race!
• For upper grades, try varying the temperature of a fluid (see the Activity Extension section).

tudents are introduced to the similarities and differences in the behaviors of elastic solids and viscous fluids. In addition, fluid material properties such as viscosity are introduced, along with the methods that engineers use to determine those physical properties.

Students are introduced to Pascal's law, Archimedes' principle and Bernoulli's principle. Fundamental definitions, equations, practice problems and engineering applications are supplied.

Students learn why engineers must understand tissue mechanics in order to design devices that will be implanted or used inside bodies, to study pathologies of tissues and how this alters tissue function, and to design prosthetics. Students learn about collagen, elastin and proteoglycans and their ro...

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The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: January 11, 2022

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How to Measure Viscosity

Last Updated: January 12, 2023 Fact Checked

This article was co-authored by Bess Ruff, MA . Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 482,415 times.

Viscosity can be defined as the measurement of a liquid's resistance to flow, also referred to as a liquid's internal friction. Consider water and molasses. Water flows relatively freely, while molasses is less fluid. Because molasses is more resistant to flow, it has a higher viscosity than water. While there are a number of methods from which to choose in deciding how to measure viscosity, perhaps the least complicated involves dropping a ball into a clear container of the liquid for which you are trying to determine viscosity.

Understanding Viscosity

Measuring Viscosity

• The sphere can be a small marble or steel ball. Make sure its diameter is no greater than half the diameter of the graduate cylinder so it can easily be dropped into the cylinder.
• A graduated cylinder is a plastic container that has graded markings on the side that allow you to measure volume.
• You can use a watch instead of a stopwatch, but your measurements will be more accurate with a stopwatch.
• The liquid must be clear enough to see the marble as it’s dropped through the liquid. Try testing many different liquids with different flow rates to see how their viscosities differ. Some common liquids you could try including water, honey, corn syrup, cooking oil, and milk.

• Measure the mass by placing the sphere on a balance. Record the mass in grams (g).
• Determine the volume of a sphere using the formula V= (4/3) x π x r 3 , where V is volume, π is the constant 3.14, and r is the radius of the sphere. You can find the radius by measuring around the center of the sphere to get its circumference and then dividing the circumference by 2π.
• You can also find volume by measuring the displacement of water in a graduated cylinder. Record the initial water level, place the sphere in the water, and record the new water level. Subtract the initial from the new water level. This number equals the volume of your sphere in milliliters (mL).

• Measure the mass of the liquid by first weighing the empty graduated cylinder. Pour your liquid into the graduated cylinder and then weigh it again. Subtract the mass of the empty cylinder from that of the cylinder with the liquid in it to obtain the mass of the liquid in grams (g).
• To find the volume of the liquid, simply determine the amount of liquid you poured into the graduated cylinder by using the graded markings on the side of the cylinder. Record the volume in milliliters (mL).

• Draw a mark at the top of the cylinder about 2.5 centimeter (1 in) (1 in) from the top of the liquid.
• Draw a second mark about 2.5 centimeter (1 in) (1 in) from the bottom of the graduated cylinder.
• Measure the distance between the top and bottom marks. Place the bottom of the ruler at the bottom mark and record the distance to the top mark.

• Liquids with low viscosities are going to be more difficult to measure with this method because it will be harder to accurately start and stop the stopwatch.
• Repeat this step at least three times (the more times you repeat, the more accurate your measurement will be) and average the three times together. To find the average, add up the times for each trial and divide by the number of trials you performed.
• This works best if the ball is small enough that the flow around the ball is truly viscous and far from turbulent. The ball must also be much smaller than the container so the ball can be dropped at least 10 ball-radii from the side walls.

• For example, let’s say the density of your fluid is 1.4 g/mL, the density of your sphere is 5 g/mL, the radius of the sphere is 0.002 m, and the velocity of the sphere is 0.05 m/s.
• Plugging into the equation: viscosity = [2(5 – 1.4)(9.8)(0.002)^2]/(9 x 0.05) = 0.00062784 Pa s

Expert Q&A

• Keeping a data table may help you keep track of your measurements where you otherwise may get disorganized. Thanks Helpful 1 Not Helpful 0
• All measurements should be metric. Thanks Helpful 1 Not Helpful 0
• Don’t forget to add units at the end of the calculation. Thanks Helpful 1 Not Helpful 0

• The ball that you use must have a higher density than the liquid for this process to work. Thanks Helpful 1 Not Helpful 0
• When you fill the graduated cylinder with the liquid, make a point not to come too close to the top. If you don't leave sufficient space, the displacement of the liquid caused by the sphere may result in overflowing, which would throw off your calculations. Thanks Helpful 1 Not Helpful 0
• Make sure there is not any water or other liquid in the graduated cylinder when you begin. The presence of another liquid could make your measurements inaccurate. Thanks Helpful 1 Not Helpful 0
• Clean the liquid off of the sphere and dry it thoroughly between runs before you drop it into the graduated cylinder. Thanks Helpful 0 Not Helpful 1

Things You'll Need

• Small solid ball or sphere-shaped object that does not float on the liquid you are using
• Liquid to be measured
• Graduated cylinder bigger around than the sphere
• Meter stick or another metric ruler
• Grease pencil
• Scale or balance

You Might Also Like

• ↑ http://physics.info/viscosity/
• ↑ http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html
• ↑ https://sciencing.com/calculate-viscosity-6403093.html
• ↑ http://www.physicsclassroom.com/class/1DKin/Lesson-5/Acceleration-of-Gravity
• ↑ https://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_surg/cub_surg_lesson03_activity1.xml

About This Article

To measure viscosity, fill a graduated cylinder with the liquid to be measured and mark the liquid's positions at the top and bottom of the cylinder. Drop a marble into the liquid and start a stopwatch, then record the time it takes for the ball to drop between the marks. Calculate the velocity of the sphere, then plug the information you've gathered into the viscosity formula to get your answer! To learn more about the concept of viscosity, read on! Did this summary help you? Yes No

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2.6: Viscosity

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• Page ID 55849
• Pavan M. V. Raja & Andrew R. Barron
• Rice University via OpenStax CNX

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Introduction

All liquids have a natural internal resistance to flow termed viscosity. Viscosity is the result of frictional interactions within a given liquid and is commonly expressed in two different ways.

Dynamic Viscosity

The first is dynamic viscosity, also known as absolute viscosity, which measures a fluid’s resistance to flow. In precise terms, dynamic viscosity is the tangential force per unit area necessary to move one plane past another at unit velocity at unit distance apart. As one plane moves past another in a fluid, a velocity gradient is established between the two layers (Figure \(\PageIndex{1}\) ). Viscosity can be thought of as a drag coefficient proportional to this gradient.

The force necessary to move a plane of area A past another in a fluid is given by Equation \ref{1} where \(V\) is the velocity of the liquid, Y is the separation between planes, and η is the dynamic viscosity.

\[ F = \eta A \frac{V}{Y} \label{1} \]

V/Y also represents the velocity gradient (sometimes referred to as shear rate). Force over area is equal to τ, the shear stress, so the equation simplifies to Equation \ref{2} .

\[ \tau = \eta \frac{V}{Y} \label{2} \]

For situations where V does not vary linearly with the separation between plates, the differential formula based on Newton’s equations is given in Equation \ref{3}.

\[ \tau = \eta \frac{\delta V}{\delta Y} \label{3} \]

Kinematic Viscosity

Kinematic viscosity, the other type of viscosity, requires knowledge of the density, ρ, and is given by Equation \ref{4} , where v is the kinematic viscosity and the \(\eta \) is the dynamic viscosity.

\[ \nu = \frac{\eta }{\rho } \label{4} \]

Units of Viscosity

Viscosity is commonly expressed in Stokes, Poise, Saybolt Universal Seconds, degree Engler, and SI units.

The SI units for dynamic (absolute) viscosity is given in units of N·S/m 2 , Pa·S, or kg/(m·s), where N stands for Newton and Pa for Pascal. Poise are metric units expressed as dyne·s/cm 2 or g/(m·s). They are related to the SI unit by g/(m·s) = 1/10 Pa·S. 100 centipoise, the centipoise (cP) being the most used unit of viscosity, is equal to one Poise. Table \(\PageIndex{1}\) shows the interconversion factors for dynamic viscosity.

The CGS unit for kinematic viscosity is the Stoke which is equal to 10 -4 m 2 /s. Dividing by 100 yields the more commonly used centistoke. The SI unit for viscosity is m 2 /s. The Saybolt Universal second is commonly used in the oilfield for petroleum products represents the time required to efflux 60 milliliters from a Saybolt Universal viscometer at a fixed temperature according to ASTM D-88. The Engler scale is often used in Britain and quantifies the viscosity of a given liquid in comparison to water in an Engler viscometer for 200cm 3 of each liquid at a set temperature.

Newtonian versus Non-Newtonian Fluids

One of the invaluable applications of the determination of viscosity is identifying a given liquid as Newtonian or non-Newtonian in nature.

• Newtonian liquids are those whose viscosities remain constant for all values of applied shear stress.
• Non-Newtonian liquids are those liquids whose viscosities vary with applied shear stress and/or time.

Moreover, non-Newtonian liquids can be further subdivided into classes by their viscous behavior with shear stress:

• Pseudoplastic fluids whose viscosity decreases with increasing shear rate
• Dilatants in which the viscosity increases with shear rate.
• Bingham plastic fluids, which require some force threshold be surpassed to begin to flow and which thereafter flow proportionally to increasing shear stress.

Measuring Viscosity

Viscometers are used to measure viscosity. There are seven different classes of viscometer:

• Capillary viscometers.
• Orifice viscometers.
• High temperature high shear rate viscometers.
• Rotational viscometers.
• Falling ball viscometers.
• Vibrational viscometers.
• Ultrasonic Viscometers.

Capillary Viscometers

Capillary viscometers are the most widely used viscometers when working with Newtonian fluids and measure the flow rate through a narrow, usually glass tube. In some capillary viscometers, an external force is required to move the liquid through the capillary; in this case, the pressure difference across the length of the capillary is used to obtain the viscosity coefficient.

Capillary viscometers require a liquid reservoir, a capillary of known dimensions, a pressure controller, a flow meter, and a thermostat be present. These viscometers include, Modified Ostwald viscometers, Suspended-level viscometers, and Reverse-flow viscometers and measure kinematic viscosity.

The equation governing this type of viscometry is the Pouisille law (Equation \ref{5} ), where Q is the overall flowrate, ΔP, the pressure difference, a , the internal radius of the tube, η, the dynamic viscosity, and l the path length of the fluid.

\[ Q\ =\frac{\pi \Delta Pa^{4}}{8\eta l} \label{5} \]

Here, Q is equal to V/t; the volume of the liquid measured over the course of the experiment divided by the time required for it to move through the capillary where V is volume and t is time.

For gravity-type capillary viscometers, those relying on gravity to move the liquid through the tube rather than an applied force, Equation \ref{6} is used to find viscosity, obtained by substituting the relation Equation \ref{5} with the experimental values, where P is pressure, ρ is density, g is the gravitational constant, and h is the height of the column.

\[ \eta \ =\frac{\pi gha^{4}}{8lV} \rho t \label{6} \]

An example of a capillary viscometer (Ostwald viscometer) is shown in Figure \(\PageIndex{2}\).

Orifice Viscometers

Commonly found in the oil industry, orifice viscometers consist of a reservoir, an orifice, and a receiver. These viscometers report viscosity in units of efflux time as the measurement consists of measuring the time it takes for a given liquid to travel from the orifice to the receiver. These instruments are not accurate as the set-up does not ensure that the pressure on the liquid remains constant and there is energy lost to friction at the orifice. The most common types of these viscometer include Redwood, Engler, Saybolt, and Ford cup viscometers. A Saybolt viscometer is represented in Figure \(\PageIndex{3}\).

High Temperature, High Shear Rate Viscometers

These viscometers, also known as cylinder-piston type viscometers are employed when viscosities above 1000 poise, need to be determined, especially of non-Newtonian fluids. In a typical set-up, fluid in a cylindrical reservoir is displaced by a piston. As the pressure varies, this type of viscometry is well-suited for determining the viscosities over varying shear rates, ideal for characterizing fluids whose primary environment is a high temperature, high shear rate environment, e.g., motor oil. A typical cylinder-piston type viscometer is shown in Figure \(\PageIndex{4}\).

Rotational Viscometers

Well-suited for non-Newtonian fluids, rotational viscometers measure the rate at which a solid rotates in a viscous medium. Since the rate of rotation is controlled, the amount of force necessary to spin the solid can be used to calculate the viscosity. They are advantageous in that a wide range of shear stresses and temperatures and be sampled across. Common rotational viscometers include: the coaxial-cylinder viscometer, cone and plate viscometer, and coni-cylinder viscometer. A cone and plate viscometer is shown in Figure \(\PageIndex{5}\).

Falling Ball Viscometer

This type of viscometer relies on the terminal velocity achieved by a balling falling through the viscous liquid whose viscosity is being measured. A sphere is the simplest object to be used because its velocity can be determined by rearranging Stokes’ law Equation \ref{7} to Equation \ref{8} , where r is the sphere’s radius, η the dynamic viscosity, v the terminal velocity of the sphere, σ the density of the sphere, ρ the density of the liquid, and g the gravitational constant

\[ 6\pi r\eta v\ =\ \frac{4}{3} \pi r^{3} (\sigma - \rho)g \label{7} \]

\[ \eta\ =\frac{\frac{4}{3} \pi r^{2}(\sigma - \rho)g}{6\pi v} \label{8} \]

A typical falling ball viscometric apparatus is shown in Figure \(\PageIndex{6}\).

Vibrational Viscometers

ften used in industry, these viscometers are attached to fluid production processes where a constant viscosity quality of the product is desired. Viscosity is measured by the damping of an electrochemical resonator immersed in the liquid to be tested. The resonator is either a cantilever, oscillating beam, or a tuning fork. The power needed to keep the oscillator oscillating at a given frequency, the decay time after stopping the oscillation, or by observing the difference when waveforms are varied are respective ways in which this type of viscometer works. A typical vibrational viscometer is shown in Figure \(\PageIndex{7}\).

Ultrasonic Viscometers

This type of viscometer is most like vibrational viscometers in that it is obtaining viscosity information by exposing a liquid to an oscillating system. These measurements are continuous and instantaneous. Both ultrasonic and vibrational viscometers are commonly found on liquid production lines and constantly monitor the viscosity.

Measurement of Viscosity in a Vertical Falling Ball Viscometer

A number of methods are used to measure the viscosity of fluids. These are typically based on one of three phenomena—a moving surface in contact with a fluid, an object moving through a fluid, and fluid flowing through a resistive component. These phenomena utilize three major viscometers in the industry, i.e., a rotating viscometer , a falling-ball viscometer , and a capillary viscometer. The falling ball viscometer typically measures the viscosity of Newtonian liquids and gases. The method applies Newton’s law of motion under force balance on a falling sphere ball when it reaches a terminal velocity. In Newton’s law of motion for a falling ball, there exist buoyancy force, weight force, and drag force, and these three forces reach a net force of zero. The drag force can be obtained from Stokes’ law, which is valid in Reynolds numbers less than 1. 1–3

The falling ball viscometer is well-suited for measuring the viscosity of a fluid, and the method has been stated in international standards. 4,5 In the international standards, the method differs from the principle described in Refs. 1–3. The standards describe an inclined-tube method in which the tube for the falling ball was inclined at 10° to the vertical. Moreover, six balls were used with different diameters for various dynamic viscosity measurement ranges, and a suitable ball can be selected when the fall times of the ball are not lower than the minimum fall times recorded during a testing procedure. The rolling and sliding movement of the ball through the sample liquid are at times in an inclined cylindrical measuring tube. The sample viscosity correlates with the time required by the ball to drop a specific distance, and the test results are given as dynamic viscosity.

Brizard et al. 6 developed an absolute falling ball viscometer and made it possible to cover a wide range of viscosities while maintaining a weak uncertainty. This method considered the effect of edge, inertia, etc., and corrected the measurement result to reach a relative uncertainty on the order of 0.001. Capper Ltd. (Stoke-on-Trent, Staffordshire, U.K.) devised an improved instrument (patent no. GB1491865) for the measurement of viscosity. The instrument applied the first and second coils at different known positions around the falling tube to record the falling time in order to avoid human error. Nevertheless, the apparatus is limited in application for a stainless steel ball.

Although the falling ball method has been well developed and is stated in the international standards, it is somewhat inconvenient to operate this type of viscometer. For example, the viscometer requires six different diameter balls to measure a varying range of viscosities, and the user must run tests to select a suitable ball. Moreover, it is difficult to determine where the falling ball arrives at the terminal velocity, i.e., whether the distance between the beginning record line and the starting fall position is sufficient. Additionally, the inclined-tube viscometer is 10° to the vertical; thus the falling ball is not just falling down but is also rolling down. This phenomenon is different from the conditions in the derivation of the falling ball method. 1–3 Therefore, the purpose of this study was to develop a new method based on the traditional falling ball method, while deriving a dynamic equation for describing falling ball behavior in a vertical tube. Because this type of viscometer is vertical to the ground, it will be referred to here as a vertical falling ball viscometer.

A falling ball viscometer has a sphere ball that falls down along a tube containing the sample liquid to be measured, and this tube is surrounded concentrically by a tubular jacket for thermal control. The previous theory used Newton’s law of motion for describing the falling ball reaching a terminal velocity; thus, the net force of gravity, buoyancy, and drag is zero:

The drag force is expressed in the third term on the right side of the equal sign according to Stokes’ law, which is valid in Ref. 1. Eq. (1) can be easily expressed in the following form:

Where γ is the specific weight, d is the diameter of the sphere, and u t   is the terminal velocity. The subscripts s and f represent the sphere and fluid, respectively. Eq. (2) can be simplified to the following form and is the same as that claimed in the standard 4 :

Where l is the falling length and t is the time passing the length of l .

When the material properties, geometric properties, and falling time are known, the viscosity can be obtained from Eq. (2) or (3). In the standards, 4,5 the coefficient of K must be estimated by measuring a reference liquid with a known viscosity. Then, the viscosity of an unknown liquid can easily be calculated in Eq. (3), when the falling time is known.

The present study focuses on the motion of a sphere ball falling from the beginning to the end; thus it exists in the acceleration term in Newton’s law of motion:

Eq. (4) can be expressed in the following form after substituting the volume expression of a sphere:

Figure 1 - Drag coefficient versus Reynolds number of a sphere moving in liquid.

The drag coefficient of a sphere, C d , has been tested and the results plotted against the Reynolds number. 7–9 Assuming the inertia terms in the equation of motion of a viscous fluid can be disregarded in favor of the terms involving the viscosity, Stokes’ law states the drag coefficient as the form, C d = 24/Re. Figure 1 depicts the drag coefficient versus Reynolds number with the experimental results and two curve-fitting lines. The solid square, dashed line, and continuous line represent the experimental data, the line of Stokes’ expression, and the line of C d = 30/Re, respectively. It is clear that the continuous line is preferable to the dashed line based on the matching of the solid square when the Reynolds number is less than 5. Therefore, the study selects the relationship between the drag coefficient and the Reynolds number as follows:

The study substitutes Eq. (6) for Eq. (5), and the following form is obtained:

The initial conditions were:

The exact expression of Eq. (7) can be solved as follows:

In Eq. (9) it is difficult to find an explicit expression for the viscosity through the known parameters and the falling time, because the viscosity is implicit in the equation. Therefore, the study designed a numerical program to pursue the viscosity in Eq. (9) by the iteration scheme. The process of the numerical program is: 1) Set the parameters of material and geometry; 2) calculate the distance of y from Eq. (9) by guessing the viscosity; 3) check the relative error between the calculated distance and the falling distance, and correct the guessed value of viscosity; 4) repeat steps 2 and 3 until the relative error of distance is below the convergence criteria; 5) check the Reynolds number to see if it is less than 5. If it is not, the result must be discarded and the ball replaced with another of different density or diameter.

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Viscosity is a function of:

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Viscosity of Liquids Science Experiment

Viscosity? If you’ve never heard this word before you might think it’s a new brand of kitchen cleaner! But of course, if it’s not a kitchen cleaner, what in the world is it?

We’ll help define viscosity in our easy to understand explanation of how it works below, but the goal of this experiment is to help kids ‘see’ viscosity in action.

Collect your materials, print out our detailed instructions, and watch our demonstration video to explore how the consistency of a liquid impacts objects.

JUMP TO SECTION: Instructions | Video Tutorial | How it Works

Supplies Needed

• 4 clear glass jars of the same size (we used pint-sized mason jars)
• Water (enough to fill one jar)
• Corn Syrup (enough to fill one jar)
• Cooking Oil (enough to fill one jar) We used Vegetable Oil, but any Cooking Oil will work.
• Honey (enough to fill one jar)

Viscosity of Liquids Science Lab Kit – Only $5

Use our easy Viscosity of Liquids Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Viscosity of Liquids Science Experiment Instructions

Step 1 – Gather four clear glass jars and fill one with water, one with corn syrup, one with cooking oil (we used vegetable oil, but any cooking oil will work) and one with honey.

As you are pouring the liquids, take a moment to make observations. What do you notice as you pour the water into the glass? What about the corn syrup, the cooking oil and the honey? Did you notice anything different?

Do you think the liquid will impact what happens when a marble is placed into each jar? What do you think will happen? Write down your hypothesis (prediction) and then continue the experiment to test it out and to find out if you were correct.

Step 2 – Carefully drop one marble into each jar. Drop one marble at a time and observe what happens to the marble when it enters the liquid. You’ll notice right away that the marble behaves differently in each jar. Was your hypothesis correct? Do you know why some marbles sink to the bottom of the jar quickly and some marbles sink to the bottle of the jar slowly?

Find out the answer in the how does this experiment work section below. It also contains ideas on how you can expand on the experiment.

Viscosity of Liquids Science Experiment Video Tutorial

How Does the Science Experiment Work?

The question answered in this experiment is: how does the consistency of a liquid impact how long it will take for a marble to sink in a jar of that liquid? A unique property of liquids is something called viscosity.

Viscosity is a liquid’s resistance to flowing.

Viscosity depends on the size and shape of the particles that make the liquid, as well as the attraction between the particles. Liquids that have a LOW viscosity flow quickly (ie. water, rubbing alcohol, and vegetable oil). Liquids that have a HIGH viscosity flow slowly (ie. honey, corn syrup, and molasses). Viscosity can also be thought of as a measure of how “thick” a liquid is. The more viscous (or thick) a liquid is, the longer it will take for an object to move through the liquid.

In our experiment, the marbles took longer to sink when dropped into the jars filled with corn syrup and honey than they did when dropped into the jars filled with water and cooking oil. Therefore, we’ve shown that corn syrup and honey have a higher viscosity (or are more viscous) than water and cooking oil.

More Science Fun

• How long will it take? Expand on the experiment, by estimating how long it will take for the marble to sink to the bottom of the jar? Then set a timer and find out how close your estimate was. Tip: Timing the marble, works best when using liquids that have a high viscosity (ie. honey, corn syrup, and molasses).
• The Pouring Test – When you are finished dropping the marbles into the jars, try pouring the liquids one at a time into another jar. You will notice that it takes longer to pour out the Corn Syrup and Honey than it does to pour out the Water and Cooking Oil. This is because the viscosity of a liquid can also be observed by how slow (or fast) it takes to pour the liquid.
• How Does the Consistency of a Liquid Impact Magnetic Attraction – This experiment shows how the viscosity of a liquid impacts how fast (or slow) the objects move toward a magnet.

I hope you enjoyed the experiment. Here are some printable instructions:

Viscosity of a Liquid Experiment Science Experiment

• 4 clear glass jars of the same size (we used pint sized mason jars)
• Cooking Oil (enough to fill one jar)

Instructions

• Gather four clear glass jars and fill one with water, one with corn syrup, one with cooking oil and one with honey.
• Carefully drop one marble into each jar. Drop one marble at a time and observe what happens to the marble when it enters the liquid. Which marbles sink to the bottom of the jar quickly and which marbles sink to the bottle of the jar slowly.

Reader Interactions

December 13, 2017 at 5:00 pm

The honey and corn syrup has a higher density than the water and oil because ther are more particals in a certain amount of space making it slower for the marball to sink to the bottom.

April 28, 2019 at 1:51 pm

Some liquids are less dense. Some liquids are more dense. The denser liquids make the marbles flow slower. The less dense liquids (water and oil) make the marbles flow faster. The more dense liquids (honey and corn syrup) make the marbles flow slower.

September 17, 2019 at 7:37 am

Viscosity is a measure of a fluid’s resistance to flow. It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion 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 it is to do with the size and shape of the molecule rather than the density. If you heat up a liquid the density will change slightly but the viscosity will change a lot.

August 22, 2020 at 12:33 am

Honey is much thicker than oil, so the process is a little slower than the marble goes to the bottom of the honey.

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• Physics Article
• To Determine The Coefficient Of Viscosity Of Given Viscous Liquid By Measuring Terminal Velocity Of Given Spherical Body

To determine the coefficient of viscosity of a given viscous liquid by measuring the terminal velocity of a given spherical body

Coefficient of viscosity is used to calculate the viscosity of the liquid. Below is an experiment on how to determine the coefficient of viscosity of a given viscous liquid by measuring the terminal velocity of a given spherical body.

To determine the coefficient of viscosity of a given viscous liquid by measuring terminal velocity of a given spherical body.

Materials Required

• A half metre high
• 5cm broad glass cylindrical jar with millimetre graduations
• Transparent viscous liquid
• One steel ball
• Screw gauge
• Stop clock/watch
• Thermometer
• Clamp with stand

What is terminal velocity?

Terminal velocity is defined as the highest velocity that is attained by an object as it falls through a fluid. When the sum of drag force and buoyancy are equal to the force of gravity, terminal velocity occurs.

What is terminal velocity formula?

Following is terminal velocity formula:

• v is the terminal velocity
• r is the radius of the spherical body
• g is the acceleration due to gravity
• ρ is the density of the spherical body
• σ is the density of the liquid
• η is the coefficient of viscosity

• Clean the glass jar and fill it with transparent viscous liquid.
• The vertical scale along the height of the jar must be clearly visible to note the least count.
• Check the tight spring of the stopwatch and also record the least count and zero error.
• Record the least count and zero error of the screw gauge.
• Determine the radius of the ball.
• Gently drop the ball in the liquid. Initially, the ball falls with an accelerated velocity until it reaches one-third height of the liquid. Then it falls with uniform terminal velocity.
• As the ball reaches some convenient division, start the stopwatch to note its fall.
• As the ball reaches the convenient lowest division, stop the stopwatch.
• Record the time taken by the ball.
• Repeat steps 6 to 9 twice for more readings.
• Record the temperature of the liquid.
• Record the observations.

Observations

Least count of vertical scale = 1 mm

Least count of stop clock/watch = …….. s

Zero error of stop clock/watch = ……. s

Pitch of screw gauge (p) = 1mm

No.of divisions on the circular scale = 100

Least count of screw gauge (LC) = 1/100 = 0.01 mm

Zero error of screw gauge (e) = …… mm

Zero correction of screw gauge (c) = (-e) = ….. mm

The diameter of the spherical ball

• Along one direction, D 1 = ….. mm
• In the perpendicular direction, D 2 = …….. mm

Terminal velocity of spherical ball

Distance fallen, S = …… cm

Time taken,

t 1 = …….. s

t 2 = …….. s

t 3 = …….. s

Calculations

The coefficient of viscosity of the liquid at a temperature (T℃) = ……. C.G.S.units

Precautions

• To watch the motion the liquid used must be transparent
• The perfectly spherical ball should be used
• Velocity should be noted only when it is constant

Sources Of Error

• The density of the liquid used must be non-uniform
• The ball used might not be perfectly spherical
• Velocity noted might not be constant

Viva Questions

Q1. Why the liquid must be transparent?

Ans: In order to see the motion of the ball, the liquid must be transparent.

Q2. How does the viscosity of liquid and gases change?

Ans: As the temperature increases, the viscosity of the liquid decreases and the viscosity of gas increase with the increase in temperature. When the pressure increases, the viscosity of liquid increases and the viscosity of the gas does not get affected.

Q3. Why does hot water move faster than cold water?

Ans: Viscosity of hot water is smaller than that of cold water. Therefore, hot water moves faster than cold water.

Q4. What is the dimensional formula of dynamic viscosity?

Ans: Following is the dimensional formula of dynamic viscosity:

Q5. What is the CGS unit of dynamic viscosity?

Ans: Poise is the CGS unit of dynamic viscosity.

Stay tuned with BYJU’S to learn more about other Physics related experiments. Following is the link for terminal velocity derivation:

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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Marble Race--in Liquid!

A kitchen science project by Science Buddies

By Science Buddies

Syrup or honey? Oil or water? Who will win in this liquid, marble-race challenge? Test the viscosity of common liquids around your house, and find out!

George Retseck

Key concepts Physics Friction Solids Liquids

Introduction Have you ever tried to squeeze honey or syrup out of a bottle at breakfast on a chilly winter morning? Do you notice that it's harder to do that than on a hot summer day? As the liquid gets colder, its viscosity, or resistance to flow, increases. Viscosity is a properly of liquids that can be very important in very different applications—from how the syrup flows out of your bottle to how blood flows through the human body to how lava flows out of a volcano. In this project you will learn a little bit about viscosity by holding a marble race!

Background You experience friction all around you. It is what allows your shoes to grip the floor so you don't slip and it's what makes your bike come to a stop when you squeeze the brakes. This type of friction is a force that resists motion between two solid objects. Liquids, however, have friction, too—not just against solids (for example, water against a drinking glass)—but also internal friction, the liquid against itself. This internal friction is called viscosity. Different liquids have different viscosities, which means some liquids flow more easily than others. You will notice this if you think about squirting water out of a bottle or squirt gun. Imagine how much harder that would be to do with cold syrup!

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There are several different ways scientists can measure the viscosity of a liquid. One method is called a "falling sphere viscometer," in which you drop a sphere (such as a marble) through a tube filled with liquid. By measuring how long it takes the marble to fall and how far it travels, you can figure out the liquid’s viscosity. You won't need to do any calculations in this activity—but you will get to "race" marbles by dropping them in different liquids. Will viscosity affect how fast the marbles fall? Try this project to find out!

About a dozen equal-size marbles

At least two equal-size tall, transparent drinking glasses (the taller the better)

Assorted liquids from around your kitchen you have permission to use, such as water, syrup, honey, molasses, olive oil, vegetable oil, etcetera

Strainer or colander

A flat surface that can have liquids (water, oil, etcetera) spilled on it—or protection (such as a large trash bag) for the surface

Optional: Extra bowls/containers and/or a funnel (for storing and reusing the liquids you use for the activity, if you do not want to throw them away)

Optional: Volunteer to help you see which marble hits the bottom first

Preparation

If you want to save and reuse the liquids you use from the activity, make sure you thoroughly wash your marbles and drinking glasses with soap and water, then dry them completely. This will assure they are clean and you do not get your liquids dirty.

Prepare a work space on your flat surface and ensure that it is ready for any accidental spills (of water, oil, etcetera).

Fill your two (or more) drinking glasses with each of your different liquids to the same height. (To avoid spilling when you drop the marbles in do not fill them all the way to the brim.)

Which liquid do you think has a higher viscosity? Can you tell when you pour them into the glasses? Do you think the marble will fall faster through one of the liquids?

Hold one marble in each hand, just above the surface of the liquid in each glass.

Watch the glasses closely. Be prepared to watch the bottom to see which marble hits first. If you have a volunteer, have them look at the glasses, too.

Let the marbles go at exactly the same time.

Observe which marble hits the bottom of the glass first.

Which marble won the "race"? Do your results match your prediction?

Repeat the activity with a few more marbles to see if you get the same results. (Use clean, dry marbles each time.)

If you have more than two different liquids, you can try racing marbles in other liquids to see what happens.

Through which liquid do the marbles fall the fastest? The slowest?

Extra: What happens if you drop different types of marbles (for example, steel marbles versus glass marbles) or different size marbles? Do the results of your races change?

Extra : What happens if you change the temperature of a liquid? Have an adult help you cool some syrup in the refrigerator and heat some on the stove or in the microwave. What happens if you do a race with cold versus warm syrup instead of room-temperature syrup? How does temperature affect the liquid’s viscosity? Is the temperature effect stronger on some liquids than it is for others?

[break] Observations and results When pouring your liquids, you might have noticed that some of them were "thicker" or harder to pour. These are the more viscous liquids. You can also think about what these liquids are like when you use them everyday. For example, what would happen if you poured water on pancakes? Would it flow slowly like syrup or spread out very quickly? What about if you tried to pour and drink a glass of syrup? Taste (and healthfulness) aside, would that be harder than drinking a glass of water?

You should have observed that the marbles fell more slowly through more viscous liquids (such as syrup) than through less viscous liquids (such as water). This is because the more viscous liquids have more resistance to flow, making it more difficult for the marble to travel through them. It might be hard to tell the difference between the results for some liquids, however—especially if your glasses are not very tall. This is why it is important to do multiple trials and have a volunteer help watch the marbles.

Cleanup If you want to keep the remaining liquids for future use, have an adult help you pour them back into storage containers. (Use the strainer to remove the marbles). Otherwise, have an adult help you dispose of the liquids properly. Be careful because pouring some viscous liquids (such as cooking oil) down the sink can clog the drain.

More to explore Race Your Marbles to Discover a Liquid's Viscosity , from Science Buddies What Is Viscosity? , from Princeton University It's a Solid… It's a Liquid… It's Oobleck! , from Scientific American Science Activities for All Ages! , from Science Buddies

This activity brought to you in partnership with Science Buddies

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• Review Article
• Published: 10 June 2024

Liquid-metal experiments on geophysical and astrophysical phenomena

• Frank Stefani   ORCID: orcid.org/0000-0002-8770-4080 1  

Nature Reviews Physics ( 2024 ) Cite this article

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• Astronomy and planetary science
• Planetary science

Recent decades have seen enormous progress in the experimental investigation of fundamental processes that are relevant to geophysical and astrophysical fluid dynamics. Liquid metals have proven particularly suited for such studies, partly owing to their small Prandtl numbers that are comparable to those in planetary cores and stellar convection zones, partly owing to their high electrical conductivity that allows the study of various magnetohydrodynamic phenomena. After introducing the theoretical basics and the key dimensionless parameters, we discuss some of the most important liquid-metal experiments on Rayleigh–Bénard convection, Alfvén waves, magnetically triggered flow instabilities such as the magnetorotational and Tayler instability, and the dynamo effect. Finally, we summarize what has been learned so far from those recent experiments and what could be expected from future ones.

Geophysical and astrophysical fluid dynamics is concerned with diverse phenomena as convection and magnetic field generation in stellar and planetary interiors or accretion onto protostars and black holes.

Liquid-metal experiments are suited for investigating these processes, partly owing to their high electrical conductivity and partly owing to their small Prandtl numbers that are comparable to those in planetary cores and stellar convection zones.

Apart from heat transport scalings, liquid-metal convection experiments have explored a wide variety of flow structures that occur in dependence on the geometric aspect ratio and the presence of magnetic fields.

Exposing liquid rubidium to a high-pulsed magnetic field has allowed to equalize the speeds of Alfvén waves and sound waves and to study their mutual transformation that is a key ingredient for heating the solar corona.

The past decades have seen enormous progress in the experimental realization of the hydromagnetic dynamo effect and of various forms of the magnetorotational instability.

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Acknowledgements

Funding from the European Research Council (ERC) under the Horizon 2020 research and innovation programme of the European Union (grant agreement number 787544) is gratefully acknowledged. The author is deeply indebted to A. Gailitis (Riga) for his leadership in the joint work on the Riga dynamo experiment, as well as to G. Rüdiger (Potsdam) and R. Hollerbach (Leeds) for the long-term collaboration on the magnetorotational and Tayler instability. Cordial thanks go to the current and former students and colleagues of the author at Helmholtz-Zentrum Dresden-Rossendorf, in particular to T. Albrecht, R. Avalos-Zuñiga, C. Kasprzyk, S. Eckert, M. Fischer, J. Forbriger, V. Galindo, F. Garcia, G. Gerbeth, A. Giesecke, T. Gundrum, U. Günther, J. Herault, G. Horstmann, P. Jüstel, E. Kaplan, M. Klevs, N. Krauter, O. Kirillov, V. Kumar, K. Liu, G. Mamatsashvili, A. Mishra, J. Ogbonna, M. Ratajczak, S. Röhrborn, J. Szklarski, M. Seilmayer, J. Šimkanin, T. Vogt, T. Weier, N. Weber, T. Wondrak and M. Xu, for all their help in solving a wide variety of problems in basic and applied magnetohydrodynamics. G. Gerbeth is also thanked for the constructive comments on the draft.

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Stefani, F. Liquid-metal experiments on geophysical and astrophysical phenomena. Nat Rev Phys (2024). https://doi.org/10.1038/s42254-024-00724-1

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