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Science Forum

  1. Standard member sonhouse
    Fast and Curious
    15 Jun '10 17:45
    So I had these auto tools in a car that is exposed to sunlight, hot day and such. The sun did not reach inside the car but I saw some strange effects on the tools. There were iron tools, chrome steel tools, red painted steel tools. By far the hottest of the bunch was the chrome steel star wrench (used to loosen tire bolts). The weird part is, that piece was mirror finish chrome, you can see yourself in the metal easily. So why is this part the hottest of the bunch, I mean not a little hotter but too hot to touch, maybe 70 degrees C, hot enough to burn my hand handling it, while the others were maybe 45 degrees, warm but not nearly so hot as the star wrench. What is going on here?
    I would have assumed the chrome steel to be the coolest because of the highly reflective surface but even a rusty iron hammer was a lot cooler, with brown rust all over the metal surface, I would assume it to collect heat more efficiently than chrome steel.
    Color me confused!
  2. 15 Jun '10 18:56
    hmm.

    http://www.glacierbay.com/Heatprop.asp


    The chart below gives the infrared radiation reflectivity (emissivity) of some common materials:

    Steel Polished 45%
    Oxidized 15%
  3. 15 Jun '10 19:03 / 1 edit
    http://aibs.businesscatalyst.com/_blog/AIBS_National_News/post/Decorative_galvanized_steel_-_the_impact_of_colour/

    (includes graph of sun-heated metal temperature for various colors of paint)
  4. 15 Jun '10 19:04
    http://www.cpsc.gov/cpscpub/pubs/5036.html

    The U.S. Consumer Product Safety Commission (CPSC) advises parents to check for hot surfaces on metal playground equipment before allowing young children to play on it. Solid steel decks, slides, or steps in direct sunlight may reach temperatures high enough to cause serious contact burn injuries in a matter of seconds.

    CPSC knows of incidents in which children suffered second and third degree burns to their hands, legs, and buttocks when they sat on metal stairs, decks, or slides. Young children are most at risk because, unlike older children who react quickly by pulling away their hands or by getting off a hot surface, very young children may remain in place when they contact a hot surface.
  5. Standard member sonhouse
    Fast and Curious
    16 Jun '10 04:09 / 1 edit
    Originally posted by zeeblebot
    http://www.cpsc.gov/cpscpub/pubs/5036.html

    The U.S. Consumer Product Safety Commission (CPSC) advises parents to check for hot surfaces on metal playground equipment before allowing young children to play on it. Solid steel decks, slides, or steps in direct sunlight may reach temperatures high enough to cause serious contact burn injuries in a matter of ...[text shortened]... ting off a hot surface, very young children may remain in place when they contact a hot surface.
    I think then the answer to my question is chrome steel, highly reflective to visible light has to be highly absorbent to IR. The weird part was it was not in direct sunlight but inside an old car. The car was hot inside, maybe 90 degrees F outside and clearly over 110F inside the car. My hand still hurts from the minor burn I got. I don't think it would have been minor if I had continued to hold that star wrench much longer.
    I just reacted instantly and threw the dam thing about 20 feet just to get it out of my hand!
  6. Subscriber AThousandYoung
    Do ya think?
    16 Jun '10 05:23
    If you study the blackbody problem you will see that things which are reflective are reflective in both directions, inside and out; and likewise for dark things which tend to absorb more but also radiate more.

    I suspect you touched these things after they had been in the sun all day but after they had a chance to cool off a little.
  7. 16 Jun '10 07:09
    I think conductivity (of heat) probably also come into it. It is possible to pick up something hot that has a low conductivity because your hand cools down the surface and it takes a while for internal heat to replace it.
    Also, a smooth surface will conduct more heat to your hand than a rough one.
  8. 16 Jun '10 10:00
    I think there are two possible explanations, both of which have been mentioned:

    - the heat conductivity of the chrome tool is high, which means it heats up quickly due to the hot air surrounding it;
    - the chrome tool absorbs IR radiation well, this means the IR radiation due to the heat in the car (the blackbody radiation) heated up the tool.
  9. Subscriber AThousandYoung
    Do ya think?
    16 Jun '10 22:44
    Oh one more - heat capacity - higher means more heat is transferred to cool off.
  10. 16 Jun '10 23:49
    Originally posted by sonhouse
    I think then the answer to my question is chrome steel, highly reflective to visible light has to be highly absorbent to IR. The weird part was it was not in direct sunlight but inside an old car. The car was hot inside, maybe 90 degrees F outside and clearly over 110F inside the car. My hand still hurts from the minor burn I got. I don't think it would hav ...[text shortened]...
    I just reacted instantly and threw the dam thing about 20 feet just to get it out of my hand!
    http://en.wikipedia.org/wiki/Germanium#Optics

    Because germanium is transparent in the infrared it is a very important infrared optical material, that can be readily cut and polished into lenses and windows. It is especially used as the front optic in thermal imaging cameras working in the 8 to 14 micron wavelength range for passive thermal imaging and for hot-spot detection in military, night vision system in cars, and fire fighting applications.[56] It is therefore used in infrared spectroscopes and other optical equipment which require extremely sensitive infrared detectors.[58]
  11. 20 Jun '10 22:07
    http://news.google.com/news/more?pz=1&cf=all&cf=all&ncl=dxd-wSsSQV6XmIMpGKaPn3Pr3LsYM


    http://www.nydailynews.com/ny_local/brooklyn/2010/06/18/2010-06-18_no_play_dates_for_hot_domes.html

    Steel domes at Brooklyn Bridge Park closed off after toddler is badly burned

    Read more: http://www.nydailynews.com/ny_local/brooklyn/2010/06/18/2010-06-18_no_play_dates_for_hot_domes.html#ixzz0rQwiP5oL