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Convection

Convection extended definition

Convection is the transfer of heat through the movement of liquids and gases.

Convection why do i care ag/K-12

Why do I care?  Convection is sometimes responsible for the formation of thunderstorms, and these thunderstorms during the summer can provide a substantial amount of rain for growers.  Convection also contributes to the wind chill effect, which can endanger people working outside on cold, windy days.

Convection prerequisites

I should already be familiar with: Temperature

Convection body


Thermal Forming and Rising

Figure A
http://apollo.lsc.vsc.edu/classes/met130/notes/chapter2/atm.conv3.htm

Convection is the transfer of heat from a warmer region to a cooler one by moving warm liquid or gas from the heated area to the unheated area. In a boiling pot of water, hot water in the bottom of the pot rises to the surface, leading to bubbles of heated water and sometimes steam visible on the surface. In meteorology, convection is often associated with rising air and clouds, and at times, thunderstorms. Air that is rising cools as it reaches lower pressures, and may reach the point where water vapor in the air condenses and forms clouds. These rising columns of air are called "thermals". Fair weather cumulus clouds often form on the top of these rising columns of air. Thunderstorms can sometimes form where there is a lot of water vapor and heating. You may have heard the TV meteorologist mention afternoon convection leading to thunderstorms on hot summer afternoons.

Air rising and falling near a heater.

Figure B
http://www.revisionworld.com/files/convection%20copy.jpg

Convection is not just limited to meteorology. In fact, many of our daily activities involve or observe convection. For example, if you drink coffee (or any hot beverage), you may notice steam rising up from your hot beverage. In this case, we can visibly observe convection as the steam is transferring heat into the air. Another example would be a heater during the winter. The heater emits warm air which will rise to the top of the room. The warm air will eventually cool and sink to the bottom of the room before getting pulled back into the heater. Over time, this process will warm and mix the air as long as the heater remains on.

Convection relation to agriculture/K-12

How does this relate to agriculture?

Cured Tobacco
Figure C: Flue-Cured Tobacco
Image from Bridget Lassiter

 

 

Convection is responsible for many of the naturally occurring processes that we see in nature every day. For example, convection can affect fog layers that are often seen on cool fall mornings, when the air close to the surface is warmer than the atmospheric air higher up. Smoke rising from a fire can also show the conduction currents present as the heated air goes up. Also, old flue-cured tobacco barns worked on the convection principle, where the heated air from the botton rose through the air to dry the tobacco that was hanging. Convection of air is also a factor in chilling warm bodies in winter when frigid air is brought into contact with skin and the heat is convected away, potentially leading to hypothermia and frostbite when wind chills are extreme.

Convection NSES

Links to National Science Education Standards:

5th grade science:  5.P.3.1 : Explain the effects of the transfer of heat (either by direct contact or at a distance) that occurs between objects at different temperatures. (conduction, convection, or radiation).

7th grade science:  7.E.1.5 : Explain the influence of convection, global winds, and the jet stream on weather and climatic conditions.

Earth Science:  EEn.1.1.4 : Explain how incoming solar energy makes life possible on Earth. (extension)

Physical Science:  PSc.3.1.1 : Explain thermal energy and its transfer.

All Activities Opening


Activities to accompany the information above:

Atmospheric Processes-Convection Activity

Activity: Atmospheric Processes-Convection  (Link to original activity).

Teacher Set-up Instructions

Student Activity: pdf document   word document

Description: This activity shows how currents move through water using food coloring and hot and cold water. This simulates how air can act as a fluid. Students will fully understand the process of convection and how heat is transferred through this process.

Relationships to topics: Convection, General Circulation of the Atmosphere, Ocean Circulations

Convection Discrepant Event

Activity: Convection Discrepant Event

Description: This activity poses a demonstration of convection and potentially water currents that should be conducted in front of the students for the students to think about what is happening during this activity. At the beginning the activity is not fully explained to students, but instead placed in front of them to create thought. This activity could be an opening into heat transfer through convection.

Relationships to topics: Convection, Ocean Circulations

Energy Webquest

ActivityEnergy Webquest

Student Activity: pdf document, word document

Description: In this activity, students review several websites that walk them through the layers of the atmosphere and energy transfer in the atmosphere.

Relationships to topics: Structure of the Atmosphere, Conduction, Convection, Radiation

Last modified date: Tuesday, August 13, 2013 - 10:08am