Why would a lightning-struck tree glow after being hit?
It is not on fire and does not give off heat, but glows.
It was a dark and stormy night. Chris emails he
was walking in the woods "a little after a thunderstorm" when he
noticed the tree. The tree, shattered by an earlier lightning
stroke, stabbed the night like a broken pike. An eerie glow extended ...
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Wind-chill experiment
Here's how you can test whether water will freeze with an ambient temperature
of 35° F (2° C) and a wind chill factor of 25° F (-4° C). First, you need a fan
since it takes a 15 mph (24 kph) wind to produce a wind chill factor of 25° F if
the air temperature is 35° F.
- Empty the refrigerator (ideally) or put the food on one shelf to allow air
flow. Take out any glass shelves or shelves that block air flow.
- Set the refrigerator to 35°; put a check thermometer in.
- Set a pan of water on the middle rack.
- Place a small battery-powered fan on the top shelf pointed at the pan of
water. A link for a $14 battery-operated fan is given below.
- Estimate the air speed from the fan onto the water by feel with your
hand. Close the refrigerator door as much as possible on your arm while
estimating the air speed. You probably can guess that the air speed is, say,
somewhere between 5 mph and 20 mph with some confidence.
- Calculate or look up the wind chill factor associated with your air speed
estimates and refrigerator temperature. A link for a lookup table is given
below.
- Stick a thermometer in the pan of water.
- Check the temperature of the water until it reaches about 35°.
- Leave the experiment going overnight to see if the water ever freezes.
Good luck!
NOAA: National
Weather Service wind chill chart
Safety Central:
$20-battery operated fan
(Answered June 27, 2003; updated Oct. 3, 2007)
Click for printer version.
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