Earth and Space Science > Activities > Fluid Viscosity

# Fluid Viscosity

#### Summary

The viscosity of a fluid describes its resistance to deformation. Water has a very low viscosity: the force of gravity causes it to flow immediately. Honey has a higher viscosity. Viscosity plays a critical role in planetary processes but students do not often intuitively understand it. In this lab students measure and calculate viscosities of liquids.

## Learning Goals

To give you a feeling for both what viscosity values are and how they are measured in the lab, we will measure fluid viscosity by dropping ball bearings into graduated cylinders of fluids.

## Context for Use

Introductory space and planetary science courses in high school or college. This activity works well with students who will work in teams of three or four and have an hour for the work, followed by discussion the next day. Easily adapted for more advanced students by including more calculations, temperature-dependent of viscosity (heated honey, for example), and topics in data analysis.

## Background

See file appended to "In-Class Activities" below.

## Description and Teaching Materials

### In-Class Activities

In-Class Activity for Fluid Viscosity Activity (Microsoft Word 45kB Jun14 10)
Background for Fluid Viscosity Activity (Acrobat (PDF) 204kB Jun14 10)

### At Home Assignments

1. Calculate viscosity separately for each ball experiment using eq. 3 from the "Background" section; record your calculations in one or more (if you break down the calculations into steps) columns in your lab notebook table.

2. Write down possible sources of error in your measurements.

### Materials

Graduated cylinders (two for each team, in our case, 10)

Rulers (one for each team, in our case, 5)

Stopwatches (one for each team, in our case, 5)

Liquids sufficient to fill graduated cylinders (honey, oil, corn syrup, detergent...there should be at least two liquids and as many as 5, and for each graduated cylinder you'll need a half liter)

Paper

Indelible pens to mark graduated cylinders

Pencils

Paper towels

## Standards

Scientific Inquiry Skills SIS1 (Make observations...), SIS3 (Analyze and interpret results...), SIS4 (Communicate and apply the results...)
This activity provides context and understanding necessary for High School Learning Standard 1: Matter and Energy in the Solar System, 3: Earth Processes and Cycles, and 4: The Origin and Evolution of the Universe.

## Teaching Notes and Tips

A discussion should be planned for the day after the students complete their at-home assignments. This discussion can include graphing data from the whole class, error analysis, standard deviations, kinds of viscosity laws (temperature-dependent, pressure-dependent, etc.), application to planetary problems, or more, depending upon the level of the students.

## Assessment

Scientific Inquiry Skills SIS1 (Make observations...), SIS3 (Analyze and interpret results...), SIS4 (Communicate and apply the results...)

This activity provides context and understanding necessary for High School Learning Standard 1: Matter and Energy in the Solar System, 3: Earth Processes and Cycles, and 4: The Origin and Evolution of the Universe.

## References and Resources

Wikipedia introductory article on viscosity - http://en.wikipedia.org/wiki/Viscosity

Wikipedia introductory article on Stokes Law - http://en.wikipedia.org/wiki/Stokes%27_law

## Fluid Viscosity -- Discussion

1. Is it important to fill each graduated cylinder up to the same height each time?
2. How can you tell which liquids are thicker and which are thinner using the concept of viscosity?
3. How do you explain your results based on the intermolecular forces that exist in the liquids you tested?
4. Why are motorists advised to use more viscous oils for their engines in the summer and less viscous oils in the winter?
5. What effect do you think molecular shape has on viscocity?

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