Viscosity is the resistance of a fluid to flow. Both liquids and gases are considered fluids. A viscous fluid has a high viscosity. That is, it does not flow easily. A less viscous fluid flows more easily. Viscosity is analogous to the friction of solid objects. Like friction, viscosity inhibits movement and serves as a mechanism for transforming kinetic energy into thermal energy. Liquids like molasses and motor oil are very viscous. Fluid viscosity varies because the internal structure of fluids also varies. Intermolecular forces play a role in viscosity; stronger attractions between molecules cause them to resist flow. Molecule size is also a factor; longer molecules can become tangled and flow slowly. When a container is tilted to allow flow, the flowing particles transfer energy to the stationary particles. The viscosity of a liquid generally increases with a decrease in temperature. Gases also have a resistance to flow, although gas viscosities are much lower than for liquids.
Student Experiment
Materials – • Lab aprons • Goggles • 3 sealed tubes, labeled A, B, and C • Test tube rack • Ruler • Stopwatch Procedures – A. As a group, examine each test tube. Observe the air bubble in each. Watch it as you tilt each tube. Your tubes contain syrup, baby oil, and water. Predict which tube contains each liquid. B. Measure the height of the liquid in each tube. Record the fluid height in the data table. C. Beginning with Tube A, invert the test tube and measure the time it takes for the air bubble to move from one end to the other through the fluid. Record the time in the data table. D. Repeat this procedure 5 times per tube and record your data. E. Compute the average speed of the bubble in each tube.
Data Table
Tube A Tube B Tube C
Distance
(cm) Time
(s) Speed
(d/t) Distance
(cm) Time
(s) Speed
(d/t) Distance
(cm) Time
(s) Speed
(d/t)
15.6 35 .45 15.4 1.5 10.27 15.6 2.6 6.0
15.6 36 .43 15.4 2 7.7 15.6 3.0 5.2
15.6 35 .45 15.4 2 7.7 15.6 2.8 5.6
15.6 37 .42 15.4 2 7.7 15.6 2.6 6.0
15.6 36 .43 15.4 1.5 10.27 15.6 2.6 6.0
Average Speed .44 Average Speed 8.73 Average Speed 5.76
In this experiment, student groups ran repeated trials (5) and then averaged their data. All BUT ONE statement explains why the students ran five trials. That is
A) The student data is more reliable.
B) Repeated trials ensure the desired results to support a hypothesis.
C) The more times you repeat the experiment, the more valid your results are.
D) The possibility of obtaining inaccurate results due to experimental errors will be less.