Friction is the force that occurs when two objects rub against one another.
Fluid friction is a little more complex than dry friction because fluid friction depends on the viscosity of the liquid. The viscous forces are frictional forces that occur in movement through fluids. When an object moves faster through a fluid, the viscous forces increase.
The viscosity of a fluid is a measure of the internal friction within that fluid. One way you can tell the viscosity of a fluid is by pouring it.
Example: Fluids that flow easily like gasoline and water, have a LOW viscosity.
Fluids that flow slowly like molasses, honey, and egg whites, have a HIGH viscosity.
This idea of viscosity can help us understand which fluids objects would flow through more easily.
To understand this more fully, we can do this experiment.
Materials:
* Clay
* Water
* Clear cups
* Karo syrup
Procedure:
1. Demonstrate for the students how water has a low viscosity because it pours easily into the first clear cup.
2. Then repeat number 1, but use Karo syrup to show how it has a high viscosity because it is harder to pour.
3. Grab two equal size pieces of clay and roll them into equal size balls.
4. With a partner, drop the two clay balls into one water cup and the other in the cup of syrup. Do this at the same exact time.
Observe:
Which liquid does the clay travel through faster? Why?
So... which liquid has the higher/lower viscosity? How do we know?
Conclusion:
When an object flows through a fluid, the viscous forces in that fluid equal out, eventually, to the applied force, so there is no acceleration. The velocity is constant, so there is no acceleration. This idea is very similar to the example of a man falling from an airplane with an open parachute. He is falling at a constant velocity, so there is no acceleration.
Works cited:
Kirkpatrick, Larry D. and Francis, Gregory E. Physics A World View 6th Edition. Thomson Brooks/Cole 2007.
Jewett, John W. Jr. The World of Physics. Thomson Brooks/Cole 2001.
The American Chemical Society. The Best of Wonder Science Vol.2 2001
This project was found in "The Best of Wonder Science Vol. 2" book, but was adapted by Angela Capone, who added a few minor differences who help better demonstrate the idea of viscosity.
For more information about projects like this one, visit The Wadsworth Education Resource Center