October, 2002, Earth Science Experiment:

Running Hot & Cold:
Convection Currents

- Purpose
- Background Information
- Equipment & Supplies
- Software & Probeware Setup
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions

PASPORT Temperature Sensor
(PS-2125)

ScienceWorkshop
Temperature Sensor
(CI-6505B)

Purpose:

Students will use a pair of Temperature Sensors to investigate convection currents in a water tank.

Background Information:

The process of convection results in the transfer of heat energy due to the movement of heated material: for example, air or water. In the environment, atmospheric convection brings day-to-day changes in the weather as wind patterns shift. Global air circulation is also influenced by convection. The cyclic patterns of air movement that result from uneven heating and cooling are called convection currents. In oceans or large bodies of water, a cycle of warm water rising and cooler water sinking will also establish a convection current.

Hypothesize: How quickly will water temperatures change as a result of heating and cooling in this activity? What kind of visual evidence will you see that indicates the establishment of a convection current?

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Equipment and Supplies:

ME-8957 -- Rotational
Acceleration Tank

For each lab group:


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Software and Probeware Setup:

  1. Ensure that your USB Links, Xplorers, or ScienceWorkshop 500 interfaces are connected to the computers.

  2. Click on one of the links below to download a pre-configured DataStudio file for this experiment, and then open the file.

    PASPORT users: Windows (.zip file) or Macintosh (.sit file)

    ScienceWorkshop 500 users: Windows (.zip file) or Macintosh (.sit file)

    When the file is opened, you should see a Graph Display of Tank Temperatures vs. Time, as well as a Digits Display of Tank Temperatures.

  3. Connect the Temperature Sensors to two Xplorers or two USB Links (PASPORT users), or plug each Temperature Sensor into channels A and B of the 500 Interface (ScienceWorkshop 500 users).

    If you are using the ScienceWorkshop 500 Interface, be sure the interface is turned on and the Temperature Sensors are associated correctly in the Experiment Setup window.

  4. Resize and arrange the displays as needed so that you can see them all.

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Experimental Procedure

Equipment Setup:

  1. Fill the tank with room-temperature water to approximately two inches from the top.

  2. Tape white paper on one side of the tank to form a backdrop against which you’ll be able to view the water currents.

  3. Clamp or position the heat lamp or light bulb at one end of the tank in order to create a warmer area of water.

  4. At the opposite end of the tank, be ready to drop the block of ice / cold pack into the water to create the cooled section of water.

  5. Position the two Temperature Sensors in the tank so that they are directly above/below one another in the middle of the tank.

Data Collection & Recording:

  1. Click the Start button ( ) to begin collecting room-temperature data. The graph should display two different-colored traces , one from each of the Temperature Sensors. Monitor the temperature for 3-5 minutes; ideally the tank conditions should be stable.

  2. Change the temperature conditions by turning on the heat source at one end and suspending the block of ice in the water at the other end of the tank.

  3. Wait approximately 5-10 minutes for the temperature change to take effect, then drop a small amount (1-2 drops) of food coloring into the water in order to make the convection currents more visible. (Hint: Consider using red coloring near the heat lamp and blue coloring near the cold pack.)

  4. Observe the temperature data and the flow of colored water to look for evidence of convection currents. Continue monitoring for approximately 15 minutes or until conditions are stable.

  5. Remove the block of ice/cold pack and turn off the heat source at the opposite end of the tank. Continue observing the temperature data and the flow of colored water in the tank.

  6. Click the Stop button ( ) when the temperature data has stabilized.


Data Analysis:

  1. Scale the axes to fit the data using the Scale to Fit button ( ) in the Graph toolbar.

  2. Use the Note Tool ( ) to annotate where on the graph environmental conditions changed -- i.e., water heated/cooled, or when lamp was turned off and ice removed.

  3. Examine the graph and study the data. At what point in the experiment were temperatures reported by each sensor farthest apart? Closest together?

  4. How did the temperatures reported by each sensor vary over the course of the experiment? Explain how this corresponded to their placement in the tank.

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Conclusions and Extensions:

  1. Describe what you observed in the heated section of the tank, and how those observations differed from your observations of the section of the tank near the ice.

  2. How did temperatures in different regions of the tank correspond to the flow of water that resulted from the convection current that was established?

  3. Explain the significance of convection currents in larger environments such as ponds, lakes or oceans.