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I am doing a science fair on insulating water with different materials, and I was hoping you could really quickly answer some questions. The insulators I'm using are: A cotton shirt, aluminum foil, Styrofoam, and a wool piece of clothing. I was wondering if you could answer if these questions:
1. Is Styrofoam a good insulator, and why or why not?
2. Is aluminum foil a good insulator, and why or why not?
3. Is a cotton shirt a good insulator, and why or why not?
4. Is a wool article of clothing a good insulator, and why or why not?
5. Of these, which do you think in the best, and why?
This interview is due on Thursday, and I was wondering if you could respond within around an hour to an hour and a half, or by 7:30 A.M. Pacific time in the morning. If you can't by either of these times, could you please respond by Friday, December 3. Thanks. Also, could you give me your name and profession and why you are an expert in this area. Sorry for pushing this on anyone to late.
And sorry about my last post, I should have read it carefully. =P
Redo Insulation Question! Sorry about my other one!
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dotheraptor
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billchapman
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Insulation question
Quick responses are hard! Here’s my attempt:
A good thermal insulator restricts the transport of heat. Heat can be conveyed via thermal conduction, convection and radiation.
Thermal conduction is thermal energy moving through matter—crystalline materials like diamond, silicon, and especially metals do this efficiently (and are therefore poor thermal insulators).
Convection conveys heat by mass transport. An extreme example is a hair dryer: The moving air (convection) conveys heat from the heating element to your hair.
Radiation is electromagnetic energy like light. Very hot objects (stars, light-bulb filaments) emit a range of wavelengths including visible ones that we can see. Warm objects emit longer-wavelength infrared radiation that is invisible but still transfers energy.
An ideal insulator would be a poor conductor, block convection and reflect radiation (particularly infrared).
Air and other gases are poor thermal conductors but can transfer heat by convection. Styrofoam is mostly air (by volume) and keeps the air trapped in small cells to frustrate convection. It’s a pretty good insulator!
By comparison, aluminum foil by itself is not a good insulator. It is reflective so it blocks heat transfer by radiation but metals conduct heat too well. (However, what would you think about Styrofoam insulation with an outer layer of aluminum foil?)
Wool and cotton insulate by trapping air (similar to Styrofoam). Of the two, I think wool clothing is often manufactured to trap air better and is hence a better insulator. Certainly this depends on details of manufacturing.
-Bill
A good thermal insulator restricts the transport of heat. Heat can be conveyed via thermal conduction, convection and radiation.
Thermal conduction is thermal energy moving through matter—crystalline materials like diamond, silicon, and especially metals do this efficiently (and are therefore poor thermal insulators).
Convection conveys heat by mass transport. An extreme example is a hair dryer: The moving air (convection) conveys heat from the heating element to your hair.
Radiation is electromagnetic energy like light. Very hot objects (stars, light-bulb filaments) emit a range of wavelengths including visible ones that we can see. Warm objects emit longer-wavelength infrared radiation that is invisible but still transfers energy.
An ideal insulator would be a poor conductor, block convection and reflect radiation (particularly infrared).
Air and other gases are poor thermal conductors but can transfer heat by convection. Styrofoam is mostly air (by volume) and keeps the air trapped in small cells to frustrate convection. It’s a pretty good insulator!
By comparison, aluminum foil by itself is not a good insulator. It is reflective so it blocks heat transfer by radiation but metals conduct heat too well. (However, what would you think about Styrofoam insulation with an outer layer of aluminum foil?)
Wool and cotton insulate by trapping air (similar to Styrofoam). Of the two, I think wool clothing is often manufactured to trap air better and is hence a better insulator. Certainly this depends on details of manufacturing.
-Bill