Colorful Convection Currents

Materials / Preparation

Review the instructions and video at Easy Science Experiments: Colorful Convection Currents

Each group of students will need:

• 4 Empty glass juice bottles or Erlenmeyer flasks (about 16 oz/500 mL)
• Source of hot water
• Source of cold water
• Food coloring
• 4-5 3x5 cards cut in half
• Large buckets or tubs (optional)
• salt (optional

Grouping

Groups of two to four

Teacher tips

Easy Science Experiments: Colorful Convection Currents includes a video demonstration. If you have never seen this activity done, you may want to review the video before trying the activity.

This hot and cold water activity can be rather messy. We encourage you to try the activity yourself before doing it in the classroom. Providing students with buckets can help to avoid major water spills during this activity. Make sure that the bottles are only stacked inside the buckets. You may want to do the activity outside. If you feel that your students will not be able to do the activity, you show the online video, but it is more powerful to have students do the experiment themselves.

Keep an ample supply of hot and cold colored water handy.

For most students, it is intuitive that hot and cold water would mix. To see the cold water staying at the bottom may challenge their assumption. This is a good thing! But it’s important that the students first set up the experiment with the hot water at the bottom. Make sure to have a thorough discussion about what is happening. For students who haven’t studied density, you may want to include some basic density concepts at this point.

Procedures

1. Review and hypothesize about differences between surface waters and deep waters in the ocean. Guide students to think about the euphotic zone and how the euphotic zone (which receives direct sunlight) would differ from the deep ocean floor. Once students have determined that deep waters are cold and dark and surface waters are warm and light have a class discussion about heat/cold rising/sinking. Ask questions such as:
   • How does a hot air balloon rise?
   • Is a room warmer at the ceiling or the floor?
   • When you open the refrigerator, why do your feet get cold?
   • Can fluids (gases and liquids) move because of temperature differences?
   • Would you expect surface waters to sink?
   • Would you expect cold waters to rise?
   • (if doing the salt extension) Do you think that other properties of ocean water might create layers?
2. Explain to students how to do the Colorful Convection Currents activity. Allow students to investigate with the hot/cold water bottles—the waters will mix when hot water is at the bottom, but not when cold is at the bottom.
3. Have a discussion about what they learned. Invite the different groups to summarize the results of their investigations. Have students predict whether the light layer (euphotic zone) in the ocean could be transferred down or if the cold, nutrient-rich waters could be transferred up. This would be a good time to discuss why light doesn’t extend below the euphotic zone if your students don’t understand. Ask how the cold, nutrient-rich waters might be brought to the surface. Accept all responses; this should be a question that the students leave Activity 2 wondering about so they don’t need any “answer” at this point. Tell the students as the class ends that they will be investigating this problem in the next class activity.

Extension

OPTIONAL: If time permits, as an extension students can also experiment with salt water of various concentrations—this will deepen the students’ understanding of layers in the water column.

Resources used

Easy Science Experiments: Colorful Convection Currents
http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-008-927