Colorful Convection Currents
Convection is one of those words that we often hear used, but we may not completely understand its meaning. Weather forecasters show how convection currents are formed when warm and cold air masses meet in the atmosphere. Convection currents are responsible for warm water currents that occur in oceans. This activity demonstrates convection currents in a very colorful fashion.
- Four empty identical bottles (mouth of the bottle should be at least 1 1/2 inches in diameter) or use our Split Demo Tank
- Access to warm and cold water
- Food coloring (yellow and blue) or Fizzers coloring tablets
- 3 x 5 inch index card or an old playing card
- Fill two bottles with warm water from the tap and the other two bottles with cold water. Use food coloring or the Fizzers coloring tablets to color the warm water yellow and the cold water blue. Each bottle must be filled to the brim with water.
- Hot over cold: Place the index card or old playing card over the mouth of one of the warm water bottles. Hold the card in place as you turn the bottle upside down and rest it on top of one of the cold water bottles. The bottles should be positioned so that they are mouth to mouth with the card separating the two liquids. You may want to do this over a sink.
- Carefully slip the card out from in between the two bottles. Make sure that you are holding onto the top bottle when you remove the card. Observe what happens to the colored liquids in the two bottles.
- Cold over hot: Repeat steps 2 and 3, but this time place the bottle of cold water on top of the warm water. Observe what happens.
If you are using our Split Demo Tank, follow these directions:
- Make sure that the tank divider is firmly in place.
- Fill one side of the tank with warm water and the other side with cold water. Use food coloring or the Fizzers tablets to color the warm water yellow and the cold water blue.
- Slowly remove the divider from the tank. As you pull out the divider, observe the changes in the tank.
How Does It Work?
Hot air balloons rise because warm air is lighter than cold air. Similarly, warm water is lighter in weight or less dense than cold water. 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. Likewise, when the water mixes in the Split Demo Tank, the less dense, cold water stays on the bottom of the tank, and the more dense, warm water moves to the top.
The movement of warm and cold water inside the bottles (or tank) is referred to as the convection current. In our daily life, warm currents can occur in oceans, like the warm Gulf Stream moving up north along the American Eastern Seaboard. Convection currents in the atmosphere are responsible for the formation of thunderstorms as the warm and cold air masses collide.
Although the bottles whose colored liquids mix are more interesting to watch, the other set of warm and cold water bottles helps to illustrate another important phenomenon that occurs in the atmosphere during the winter months. 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 more dense 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.
What are the results of temperature inversion? Air pollution is more noticeable during a temperature inversion since pollutants such as car exhaust are trapped in the layer of cold air close to the earth. As a result, state agencies in many parts of the country oxygenate automobile fuels during winter months with additives like MTBE in an attempt to reduce the harmful effects of trapped pollution. This trapped pollution is what causes the "brown cloud" effect. Wind or precipitation can help alleviate the brown cloud effect by stirring up and breaking up the layer of warm air that traps the cold air and pollution down near the surface of the earth.
- Highly Recommended Review by DSD
I performed this demo for 8th graders. Not including the prep time before class, the demo only takes a few minutes, the results are very clear to the students, and it can even be interactive. My favorite part is that the jars that are still yellow and blue are also still hot and cold, respectively. This is in contrast to the green set which has also equilibrated in temperature. Next time I do this, I will give all of the students a chance to observe the convection currents but also to touch the bottles and observe the effects of the heat directly.
(Posted on February 7, 2013)
- Wow Review by kelly
I'm going to HAVE to try this with my kids!!!
My guess is that the hot molecules are bouncing around so much that they are less dense and so they want to rise. The bottle with the hot water is already on top in one. For the other, the hot water wants to float to the top and the more dense cold water wants to sink.
(Posted on February 15, 2012)
- I did this Review by Jewell Alexander
I did this project, but I did mine with cups. So yea I made a mess, but it was actually a good project. Plus when I did it it really work. Me and my little brother did the project at my kitchen table. We made a mess, but it was worth it.
(Posted on May 10, 2012)
- Cool and to the point Review by Kathleen Guillot
This is pretty cool and would be easy to do with my 6th graders. I like the use of the 2 visuals to show the comparison; alot of kids don't get that. Its short, sweet and to the point, leaving alot of time for a conclusion to be written. Nicely done - 5 stars. KG, Georgia
(Posted on April 10, 2012)