Viscosity, Surface Tension and Temperature
2011 VIRTUAL SCIENCE FAIR ENTRY
Project Title: Do surface tension and viscosity decrease with the increasing temperature? Is there any relation between surface tension and viscosity?
Purpose: The purpose of my project is to prove that as temperature increases, viscosity and surface tension both decrease, and to determine the relationship between viscosity and surface tension with a constant temperature.
Procedure: 1). Surface tension: Put several identical glass cups on the table. Pour 0.2L water in each cup with different temperatures. Put a small piece of identical paper on the water of each cup. Put paper clips on the paper in each cup. Measure the temperature of each cup when the paper clips start to fall down. Repeat the same procedures for vinegar, Coke® and milk. 2). Viscosity: Boil water. Measure 0.2L of water eight times. Put 0.2L of water into 8 identical glass cups. Put six of the glass cups into the refrigerator. Each cup of water will remain in the refrigerator for different periods of time. Put the rest two cups on the counter for different periods of time. Pour the water through the funnel while measuring time using a stop watch for all 0.2L water to pass through the funnel. Repeat the same steps on different liquids: Coke®, milk, and vinegar.
Conclusion: In conclusion, my hypothesis is that as temperature increases, viscosity and surface tension both decrease. Since viscosity and surface tension are both properties of liquids, there is a relationship between them that surface tension varies directly as viscosity at a constant temperature. My hypothesis is correct. However, there are experimental errors and statistical errors in the project.
Difficulty of the Project
There are no hazardous substances in this project.
Time Taken to Complete the Project
The purpose of my science fair project is to prove that as temperature increases, viscosity and surface tension both decrease, and to determine the relationship between viscosity and surface tension with a constant temperature.
- paper clips
- small pieces of paper
- kitchen stove
- glass drinking cups
- measuring cup
- digital balance
- 2% milk
- Tap water
A small insect resting on the surface of a pond or a lake is a common sight in the summertime. The insect creates tiny dimples in the water’s surface, almost as if it were support by a thin sheet of rubber. In fact, the surface of water and other fluids behaves in many respects as if were an elastic membrane. This effect is known as surface tension (Moore, 1962) The reason forming the surface tension, according to the theory of Brown et al, is that, “A molecule deep within a fluid exerts attractive forces in all direction, due to the molecules that surround it on all sides. The net force on such a molecule is zero. As a molecule nears the surface, however, it experiences a net force away from the surface, since there are no fluid molecules on the other side of the surface to attract it in that direction. It follows that work must be done on molecule to move it from within a fluid to the surface, and that the energy of a fluid is increased for every molecule on its surface.” (Brown, Lemay, &Bursten, 2006) From an energy standpoint, in order to extend the area of an interface to bring molecules from the interior into the surface, work must be done against the cohesive force in the liquid. The strength of surface tension depends on intermolecular forces. As temperature increases, molecules of liquid become more active and they move more rapidly; therefore, the intermolecular forces are more instable. Surface tension decreases with increasing temperature.
Afluid flowing past a stationary surface experiences a force opposing a flow. This tendency to resist flow is referred to as the viscosity of a fluid. Fluids like air have low viscosities, thicker fluids like water are more viscous, and fluids like honey and motor oil are characterized by high viscosity. Viscosity describes a fluid’s internal resistance to flow and may be thought of a measure of fluid friction. The greater a liquid’s viscosity, the more slowly it flows. Viscosity can be measured by timing how long it takes a certain amount of the liquid to flow through a thin tube under gravitational force. More viscous liquids take longer. Viscosity can also be determined by measuring the rate at which steel spheres fall through the liquid. The spheres fall more slowly as the viscosity increases. Viscosity is related to the ease with which individual molecules of the liquid can move with respect to one another. It thus depends on the attractive forces between molecules and on whether structural features exist that cause the molecules to become entangled. As temperature increases, the average kinetic energy of the molecules is greater; it is more easily overcomes the attractive forces between molecules. Therefore, viscosity decreases with increasing temperature (Physics Hypertextbook, n. d.).