Thermal Conduction

​Have you ever gone to a playground and slid down a metal slide, only for it to burn your skin a little bit where you touch the metal? If you compared the heat of two slides, one metal and the other plastic, you would find the metal slide to be much hotter to touch. This is because of thermal conduction. In the summer heat, metal feels hotter than wood or plastic because its ability to conduct heat is so much better.

There are many examples of heat conducting objects in the household: a traditional oven will heat a metal coil on the bottom of the oven, which heats the air inside by way of conduction (and convection when a fan is used). On a larger scale, we know that the heat source for our planet is the sun. Energy from the sun is transferred through space and through the earth's atmosphere to the earth's surface. Since this energy warms the earth's surface and atmosphere, some of it is transformed into heat energy.
 
Conduction is the transfer of heat energy from one substance to another, or within a substance. Have you ever left a metal spoon in a pot of soup being heated on a stove? After a short time the handle of the spoon will become hot. This is due to transfer of heat energy from molecule to molecule or from atom to atom. We also observe this when objects are welded together; the metal becomes hot (the orange-red glow) by the transfer of heat from an arc. This is a very effective method of heat transfer in metals!
 
Convection is similar to conduction, except instead of transferring heat between objects, convection is the transfer of heat energy through fluids. This type of heating is most commonly seen in the kitchen when you see liquid boiling.

Air in the atmosphere acts as a fluid. The sun's radiation strikes a surface, thus warming it. As the surface's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This is why you can feel how warm an object is by holding your hand just barely above it.
 
Test it at Home!
 
You can find out the thermal conductivity of different materials relatively easily at home! You’ll only need a few objects that have a flat/smooth surface. Try these for starters:
 

• A piece of metal
  
• A piece of wood
  
• A plastic plate
  
• A styrofoam plate
  

 
 
Place all of your materials out in the sun for about 10-15 minutes. Make sure it isn’t too windy so nothing blows away! Next, you’ll need to grab as many ice cubes as there are different materials. If you have a scale, you should measure the masses of the ice cubes to make sure they all have relatively the same mass.

Before the ice melts too much, place an ice cube on each of the materials that have been sitting in the sun. Use a timer and watch the ice to see which of the cubes melts the fastest. The material that has the ice that melts first will be the material with the highest thermal conductivity. The material with the lowest conductivity will have ice that is the last to melt! Did you expect these results? What do you think could be used in another experiment to test the conductivity of different materials?
 
 
References:
 
“The Transfer of Heat Energy”. National Weather Service, National Oceanic and Atmospheric Administration.
 
 
Image Credits:
 
Gruhl, Teodoro. “Slide”. Released into the public domain. Uploaded on 6/20/17 from publicdomainpictures.net
 
Seoane, Xoan. “Cooking on a Low Heat”. Released into the public domain. Uploaded on 6/20/17 from publicdomainpictures.net
 
“Ice Cubes for Beverages”. Released into the public domain. Uploaded on 6/20/17 from commons.wikimedia.org