Outreach 2014

 

CANDAC Outreach

Title: Convection Currents

Grade Level: Elementary

Subject: Science and Technology

Duration and frequency of activity: 40 minutes

 

Lesson at a glance

Students learn how temperature and pressure affect air density, which results in atmospheric circulation.

Focus question(s)

What is convection? What causes atmospheric circulation?

Background

Convection is the concerted, collective movement of ensembles of molecules within fluids (i.e. liquids, gases).

When the bottle of warm water is placed on top of the cold water, the more dense cold water stays in the bottom bottle and the less dense warm water is confined to the top bottle. However, when the cold water bottle rests on top of the warm water, the less dense warm water rises to the top bottle and the cold water sinks. The movement of water is clearly seen as the yellow and blue food coloring mix, creating a green liquid. The movement of warm and cold water inside the bottles is referred to as the convection current. In our daily life, warm currents occur in oceans; for example, the North Atlantic Current is often considered part of the wind-driven Gulf Stream which goes further east and north from the North American coast, across the Atlantic and into the Arctic Ocean. Convection currents in the atmosphere are responsible for atmospheric circulation, as well as the formation of thunderstorms as the warm and cold air masses collide.

During daylight hours, the sun heats the surface of the earth and the layer of air closest to the earth. This warm air rises and mixes with other atmospheric gases. When the sun goes down, the less dense warm air high up in the atmosphere often blankets the colder air that rests closer to the surface of the earth. Because the colder air is denser than the warm air, the colder air is trapped close to the earth and the atmospheric gases do not mix. This is commonly referred to as temperature inversion.

Instructions



 

1. Fill two bottles with hot water (right to the very top) and place one drop of yellow food colouring into each.

2. Fill another two bottles with cold water (right to the very top) and place one drop of blue food colouring into each.

3. Take a playing card and place it over the mouth of one of the bottles filled with cold water.

4. With one hand holding the card in place, turn the bottle upside down

5. Carefully place this bottle onto the mouth of a hot bottle.

6. Once the mouths are lined up, gently remove the card and watch what happens!

7. Repeat the same process with the other 2 bottles, but this time place the hot bottle on top of the cold bottle.

8. Lead a classroom discussion by asking students the following questions:

a) What properties affect the density of a liquid?

b) What is convection?

c) Where within the Earth’s system are convection currents known to exist?

d) What are convection cells in the atmosphere called? (Use the diagram below to point out convection cells.)

e) What does the warm water in this demonstration represent?

f) In the atmosphere, what would happen if the heat source were extinguished?

Materials

· 4 empty identical bottles (mouth of the bottle should be at least 1 1/2 inches in diameter)

· Warm and cold water

· Food coloring (yellow and blue work well)

· 2 plastic-coated playing card

Instructional method

· Oral questioning

· Hands-on demonstration

Assessment

Demonstrates an understanding convection and atmospheric circulation.

Participation in convection currents discussion.

Helpful links

· Read the article about storms in the Sahel found at http://www.sciencedaily.com/releases/2011/06/110621101323.htm with students and discuss the impact of air circulation on storms.

Extension/adaptations

· Ask students to answer the following questions in their notebook:

a) How does the formation of wind depend on convection currents?

b) Why do forest fires sometimes produce high winds?

· Have students design their own simple demonstration to represent convection currents. Ask students to create and then present their design to the class or write an explanation of the demonstration.

Source

1. University of Winnipeg (1999): “Convection.” Retrieved March 4, 2011 <http://theory.uwinnipeg.ca/mod_tech/node76.html>.

 

Diagram courtesy of NASA retrieved January 20, 2012 < http://en.wikipedia.org/wiki/File:Earth_Global_Circulation.jpg >.