Not So Great Invention #2
Trivia brain teasers have some element of trivia in them, but they are not just pure trivia questions.
Not willing to give up after a failed attempt to invent a better windshield ice scraper, a would-be inventor decided that heated windshield washer fluid was the way to go. It would melt the ice with a very hot cleaning solution, thereby eliminating the need for scraping the ice off the front windshield. However, this invention proved a failure as well. Passing all tests done to insure it worked, it did indeed remove the ice effortlessly in record time. It even sold well initially, but was recalled for safety reasons.
Why?
HintWhat happens to glass if heated too fast?
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Answer
Windshields can withstand a fair bit of expansion and contraction from cold & heat. Yet in cases of extreme cold, the hot fluid caused the glass windshields to crack. The car that was used for testing was sitting still at -15 degrees Celsius but a car driving at 120 km /h creates a wind chill of -33 deg. In some northern areas temperatures of -30 are not uncommon, giving a wind chill of -56 deg., far too cold to be spraying hot liquid on a windshield.
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Comments
Rowsdower 
Jan 13, 2004
| Just a question, because I'm unsure of something: Does windchill affect inanimate objects? I think I've been told that the wind makes it FEEL that cold, but isn't it still just the regular temperature? For example: If it's 10 degrees here and 10 degrees 5 miles away, isn't the wind still just 10 degrees even if I'm driving through it? I'm really not sure...  |
od-1 
Jan 13, 2004
| That a good question i'm not really sure. I do know it does increase the rate at which things cool down but I'm not sure if the end temp is affected. I'll have to look in to it. In any case it seems it was cold enough to crack the windshields . |
cnmne 
Jan 14, 2004
| Wind chill does not affect inanimate objects. It can never be colder than the real air temperature. The wind produced by a moving car will cause heat to be disappated more quickly than when standing still. The wind chill temperature is not what will cause the windshield to crack. However, the speed at which the temperature drops from the hot liquid to the air temperature might very well cause a break. |
Bobbrt
Jan 15, 2004
| Cnmne's right. The speed of the car doesn't make the temperature lower, it just makes it get to the same final temperature faster. Also, glass doesn't crack because it's too hot or too cold. It cracks because part of it is changing temperature faster than another part. This creates stress in the glass (because half of it is trying to expand or contract and the other half isn't), causing the crack. The key to this teaser is the SPEED at which the glass changes temperature, not the temperature itself. |
od-1
Jan 16, 2004
| WELL there you have it thanks guys for the technical explanation,  |
Jon0513
Jan 18, 2004
| i like these not so great inventions!  |
batti_s
Jan 19, 2004
| nice puzzle od!!!
bobbrt is right about the differential heating that causes glass to crack. that is the reason why very hot liquids are not poured fast into glass tumblers. |
kcelf27
Apr 26, 2005
| Boy do I feel dumb. You guys are all to technical. It's amazing what you can learn while having fun!!! |
froggygg
Apr 28, 2005
| Many, many years ago I just had to test out the do not put a hot piece of glass into (or pour into) cold water. Guess what?! I'll never use that measuring pitcher again!!! It works the same as your teaser and the cold windshield and hot cleaner. CRACK....Enjoyed this one even if it did remind me of my once favorite pitcher!
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snaps 
Jun 27, 2005
| Seems like the tests that were done to see if it worked weren't all that great... |
smarty_blondy
Oct 01, 2005
| As good as the first one.  |
peppamintp
Nov 07, 2005
| I knew the glass would crack but now I know why it cracks. Thanks for the info. Good teaser.  |
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