# If you leave your car windows up on a hot day.... **URL:** \ **Category:** Factual Questions\ **Created:** [July 31, 2008, 6:26pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386 "2008-07-31T18:26:03Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [July 31, 2008, 11:59pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/21 "2008-07-31T23:59:54Z")
[QUOTE=Q.E.D.] I’d say a BB or .177 pellet is much more likely than some sort of mysterious spontaneous glass shattering. [/QUOTE] Neither of those things is going to be able to shatter a car window, no way. Even the most powerful .177 pellet rifles [around](http://www.cabelas.com/cabelas/en/templates/links/link.jsp?id=0055629229189a&type=product&cmCat=SEARCH&returnPage=search-results1.jsp&QueryText=.177&N=4887&Ntk=Products&Ntx=mode+matchall&Nty=1&Ntt=.177&noImage=0) are either going to bounce off or punch a hole. Even real guns tend to punch holes more than they do to shatter the actual window. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 1, 2008, 12:06am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/22 "2008-08-01T00:06:12Z")
[QUOTE=Cluricaun] Neither of those things is going to be able to shatter a car window, no way. [/QUOTE] [No way, huh?](http://media.www.dailyorange.com/media/storage/paper522/news/2002/08/28/News/Bb.Guns.Cause.Damage.Around.Neighborhood-263568.shtml) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 1, 2008, 12:18am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/23 "2008-08-01T00:18:08Z")
[QUOTE=Q.E.D.] I’d say a BB or .177 pellet is much more likely than some sort of mysterious spontaneous glass shattering. [/QUOTE] Why does it have to be ‘mysterious’? Glass can shatter under thermal stress - and if the window was already damaged in some way, it doesn’t seem at all implausible that, say, uneven expansion due to rapid heating or cooling might provoke a failure. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [August 1, 2008, 12:27am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/24 "2008-08-01T00:27:49Z")
[QUOTE=Q.E.D.] [No way, huh?](http://media.www.dailyorange.com/media/storage/paper522/news/2002/08/28/News/Bb.Guns.Cause.Damage.Around.Neighborhood-263568.shtml) [/QUOTE] To be fair, both instances cited in that article clearly state that the gun did the shattering, not the BB. :ducks and runs: ---
**Author:** ![lobotomyboy63](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobotomyboy63/32/2900_2.png) [@lobotomyboy63](https://boards.straightdope.com/u/lobotomyboy63)\ **Post date:** [August 1, 2008, 12:31am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/25 "2008-08-01T00:31:58Z")
One of the T-top panels on my sister’s 1979 Camaro shattered in the heat. It was August, 1987 (I would know; it’s the day I got married). Anyway I guess it was the hot summer/cold winter cycle of Illinois that wore it out somehow, plus maybe some chassis flex? ---
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [August 1, 2008, 1:24am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/26 "2008-08-01T01:24:06Z")
[QUOTE=Q.E.D.] [No way, huh?](http://media.www.dailyorange.com/media/storage/paper522/news/2002/08/28/News/Bb.Guns.Cause.Damage.Around.Neighborhood-263568.shtml) [/QUOTE] That’s a college newspaper. It wouldn’t surprise me that they may have taken some liberties to “punch it up” a bit. I’ve shot at a window or two in my day with both BB guns and pellet rifles and I’ve never seen one shatter, much to my chagrin at the time. ---
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [August 1, 2008, 5:05am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/27 "2008-08-01T05:05:53Z")
We had a BB gun in college that would embed a bb a good quarter inch deep into plywood. I’m sure it could break car windows if the shooter were so inclined. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 1, 2008, 6:34am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/28 "2008-08-01T06:34:49Z")
[QUOTE=Q.E.D.] > [@Gary T](#): > > No, though at first I thought maybe a ball or rock had done it. The car was in my driveway, I was in the house and heard a loud pop/glass breaking noise. I went right out and saw the broken window. No one else was around, some of the glass was inside the car and some was outside, and I never found any object inside the car that might have caused it. In talking to the glass company, I was informed that this type of spontaneous breakage has been known to occur. I’d say a BB or .177 pellet is much more likely than some sort of mysterious spontaneous glass shattering. [/QUOTE] Sorry **Q.E.D.** but I’m not buying it. A BB weighs about 1/3 of a gram and moves at about 450FPS . A one or two ounce rock hitting a windshield at 80 mph imparts much more energy. A rock hit is not a 100% guaranteed busted windshield. A BB even less so. In my case I had a fixed side window (cargo area) in a station wagon shatter one morning on the way to work. I was in a tunnel at 70 MPH when there was a large bang! I saw the window was broken, but still in place. I pulled over and examined the damage. No crater, or tiny hole, like what a a bullet leave. Window was perfect except for the fact it was shattered. Conclusion? Bad glass tempering, causing thermal stress to shatter glass. This has also cropped in various technical journals around the world. Thermal stress fractures are not unkown. ---
**Author:** ![groman](https://avatars.discourse-cdn.com/v4/letter/g/73ab20/32.png) [@groman](https://boards.straightdope.com/u/groman)\ **Post date:** [August 1, 2008, 7:58am UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/29 "2008-08-01T07:58:07Z")
[QUOTE=Rick] Sorry **Q.E.D.** but I’m not buying it. A BB weighs about 1/3 of a gram and moves at about 450FPS . A one or two ounce rock hitting a windshield at 80 mph imparts much more energy. A rock hit is not a 100% guaranteed busted windshield. A BB even less so. [/QUOTE] The difference here is _windshield_ vs. _window_. A BB will bounce off a windshield. A BB is almost guaranteed to shatter a car window. Car windows _shatter_, windshields are laminated. There was a MythBusters where they actually tested several rear view windows of an older car that were not laminated. With a hand pumped daisy BB gun they checked how many pumps it would take to shatter it (it was tangetially related to the myth, something about putting your hand on the window to stop it from breaking), and IIRC, windows shattered even from a single pump of a daisy BB gun. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 1, 2008, 2:00pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/30 "2008-08-01T14:00:45Z")
[QUOTE=groman] The difference here is _windshield_ vs. _window_. A BB will bounce off a windshield. A BB is almost guaranteed to shatter a car window. Car windows _shatter_, windshields are laminated. [/QUOTE] Right, I wouldn’t expect a .177 or even a .22 BB or pellet to penetrate, let alone shatter, a windshield which is laminated. The other windows will shatter readiy, as they’re designed to, into little cubes. Firefighters and EMS types carry a little spring-loaded dealie that launches a carbide-tipped point which shatters out windws with ease, in order to free trapped occupants in car accidents. Not a lot of impact there, but it does the job. [Previous page](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386.md?page=1)