Abstract

Objective

The objective of this ocean science fair project is to make a model of ocean currents and measure how the heat input affects velocity of the currents.

Introduction

Ocean currents profoundly affect the weather, marine transportation, and the cycling of nutrients. Deep-ocean currents are driven by differences in the water's density. The water's density is controlled by temperature (cold water is denser than warm water) and salinity (salty water is denser than fresh water).

Deep-ocean currents are initiated in Earth's polar regions. Water flowing into the polar regions becomes cold, which increases its density. As ice is formed when the water freezes, freshwater is removed from the ocean (it has turned into ice), making the ocean water saltier. The cold water is now more dense, due to the added salts, thus it sinks toward the ocean bottom. Surface water then moves in to replace the sinking water, thus creating a current.

A global "conveyor belt" is set in motion when deep water forms in the North Atlantic, sinks, moves south, and circulates around Antarctica, and then moves northward to the Indian, Pacific, and Atlantic basins. It can take 1,000 years for water from the North Atlantic to find its way into the North Pacific!

The global conveyor belt moves water slowly, 10 centimeters (cm) per second (sec) at most, but it moves a lot of water. One hundred times the amount of water that is in the Amazon River is transported by this huge, slow circulation pattern. The water moves mainly because of differences in relative density, which you will explore in this science fair project. The goal of this science fair project is to model ocean currents, with particular focus on the role of heat in the currents' velocity.

Terms, Concepts, and Questions to Start Background Research

• Deep-ocean currents
• Density
• Salinity
• Global conveyor belt
• Velocity
• Convection
• Convection cell
• Energy transfer

Questions

• What types of currents are present in the ocean?
• How do ocean currents affect the weather?
• What is the role of ocean currents in distributing nutrients?
• From where does the energy that drives ocean currents come?

Bibliography

• National Oceanic and Atmospheric Administration. (2008). The Global Conveyor Belt. Retrieved October 15, 2008, from http://oceanservice.noaa.gov/education/kits/currents/06conveyor2.html
• Horton, J. (2008). How Ocean Currents Work. Retrieved October 15, 2008, from http://science.howstuffworks.com/ocean-current.htm/printable
• Braile, L.W. (2000). Thermal Convection and Viscosity of a Fluid. Retrieved October 15, 2008, from http://web.ics.purdue.edu/~braile/edumod/convect/convect.htm

Materials and Equipment

• Glass bread loaf dish, 1.5-qt.
• Thyme, dried (or any other dried leaf spice) (2 tsp.)
• Teaspoon
• Vegetable oil (about 4 cups)
• Measuring cup
• Spoon
• Ceramic coffee mugs (2)
• Small candles or cans of Sterno® (4)
• Lighter or matches
• Paper for sketching
• Thermometer
• Ruler
• Stopwatch
• Funnel
• Adult helper
• Lab notebook
• Graph paper

Experimental Procedure

1. Mix the vegetable oil and the thyme in the glass loaf dish.
2. Stir thoroughly to distribute the flakes of thyme. The flakes of thyme will flow with the liquid, showing the direction and velocity of any fluid flow.
3. Place the loaf dish on top of the two ceramic mugs.
4. Observe the oil and spice mixture. With no heat (energy) being added to the system, there should be little or no movement of the liquid, once it has settled.
5. Place a candle underneath the loaf dish, directly in the middle.
6. Light the candle and let the liquid heat up for a couple of minutes.
1. You can also use a can of Sterno. These produce more heat than candles do.
2. The convection should start soon after the heat is applied.
7. As the oil heats and begins to flow, observe the pattern of fluid flow (circulation) by noting the location of individual flakes of thyme over time. Write down all of your observations in your lab notebook.
1. This type of energy movement is called thermal convection, because added heat causes the fluid flow (circulation by convection) by lowering the density of the liquid.
8. Be sure to view the model several times during the experiment, both from above the dish and from the side of the dish.
9. Draw a sketch of the model in your lab notebook.
10. Draw a sketch of the circulation. Note the shape of the convection cell(s).
11. Is the pattern approximately symmetric on the two sides of the heated area? Where do you observe upward flow? Where do you see downward flow? Where do you observe horizontal flow?
12. Measure the temperature of the oil in different parts of the model.
1. What is the biggest temperature difference you can find?
2. Record the temperature in your lab notebook.
13. Measure the horizontal velocity of the convective flow near the surface of the liquid.
1. Use the ruler on the top of the container (oriented lengthwise) to measure distance.
2. Use a stopwatch to measure the time it take a single flake to move a certain distance.
3. Divide the distance by the time to get velocity (in centimeters per second).
4. For example, if the flake moves 3 cm in 4 sec, its velocity is .75 cm/sec.
14. Make another sketch of the model with arrows showing the direction and velocity of the currents.
15. Measure the velocity of the flakes in different parts of the model.
1. Are all of the measurements approximately the same? Where are the velocities the largest? Where are they the smallest? What could explain these variations in velocity? Are the directions of flow "away from" the heated central area of the container? What effects or characteristics of the model might cause variability in the velocities?
16. Add another lit candle and measure the temperature of the oil and the velocity of the flakes now. How does increasing the heat affect the velocity?
17. Add a third and fourth candle and repeat your measurements of temperature and velocity.
18. Make a graph of temperature of the oil versus the velocity of the current.

Variations

• Add an "island" made from a can or other object. Sketch the current flow around the island.
• Can you think of a way to add a "polar region" to the model, perhaps using a bag of ice? How does the current change with the polar region in place?
• Try a larger heat-resistant glass dish, like a lasagna pan. Place the candles in different regions and sketch the current flow.

• For more science project ideas in this area of science, see Ocean Sciences Project Ideas.

Credits

David Whyte, PhD, Science Buddies

Braile, L.W. (2000). Thermal Convection and Viscosity of a Fluid. Retrieved October 15, 2008, from http://web.ics.purdue.edu/~braile/edumod/convect/convect.htm

• Sterno® is a registered trademark of The Sterno Group LLC.

Last edit date: 2008-12-05 09:49:00