First, I will say that if this has already been done and posted, I wasn't able to find it. And if it has, I apologize for the redundancy.

I don't know if I'll think too hard about the reasons for my curiosity, but I did manage to satisfy it this past weekend. For a time now, I've been curious about what kind of damage a sling could do to certain objects. The most recent one is a car windshield. The results were not what I had originally expected, and what I did learn was even more interesting than I thought it would be. First, I think it would be good to say that no actual windshields, nor vehicles were harmed in this experiment.

Due to my rather short attention span, and rather long list of varying interests, I managed to acquire a two foot square piece of automotive windshield. At some point in my past I thought there was a better future for me in windshield repair than in my current job involving IT. Sanity must have returned at some point, because I'm still in IT.

Having seen the power that is generated by this weapon, I had initially expected to be able to throw a rock all the way through the windshield. Perhaps this is possible, but I now know that I did not sling with sufficient force to do this. And then there's the accuracy problem which made the piece of windshield the safest 2' x 2' square the safest place to be while I was trying to hit it for a disturbingly long time. Which also is my explanation, or excuse as to why I didn't film it...I started to get to the point where I wasn't sure which throw, if any, would actually make contact.

Now the results:

I was not able to get the rock to penetrate the laminate between the two pieces of windshield glass, no matter how hard I threw. While this might seem like failure, what did happen, at least in my opinion, was worse had this been an actual vehicle. On both sides of the laminate, the glass was completely gone where the rock had hit. The impact was so severe, and the laminate so strong, that the glass on the front of the windshield was powdered against the laminate. The rocks were about golf ball size, and the bare laminate spot on the glass was also about this same size. The backside of the windshield was also bare of glass, and the laminate was almost completely cleaned of glass. Spreading outward from the impact zone was a cone of shattered glass that extended about 6-10 feet back from the piece of windshield. Had this been a vehicle, I would imagine it would be like sitting in front of a shotgun that had just discharged a shell of broken glass. The glass was embedded in the ground in places, and every where behind the windshield, extending in a cone out to about ten feet were shards of glass that had come off the windshield.

For those of you who wonder what would happen if a rock was slung at a windshield, perhaps this will give some indication. At the very least, it is a good example of how dangerous a sling can be. I certainly wouldn't have wanted to be behind the windshield at the time of impact.

i own a few junk cars that i may try this with sometime. it'd be interesting to put a soft foam board in the drivers seat and see if i can get glass stuck in it. i've been experimenting with concrete sling bullets as well, and it may be possible to get one of them through the windshield. all else fails and i'm sure i could get a drill bit through it. may also be interesting to see if a rusty ball (stress ball) would break the glass.

Modern windshields are phenomenally strong. The damage to the interior glass is similar to what was suffered in the earliest tanks fielded in WW 1 by the British army. The armour could resist penetration by bullets and shrapnel, but the inside surface of the armour plate would flake off and zing around inside harming the crew. They had to wear face shields to protect themselves:

http://www.warrelics.eu/forum/ww1-allies-great-britain-france-usa-etc-1914-1918/tank-mask-162843/

Hm... maybe the lam is pretty tough plastic!
Plastic is rather hard to puncture, and car windshields are designed to not just shatter like normal glass for safety reasons.

just got my hands on a junk truck :D i'll post pictures of it if i can when i'm done slinging it it.

that's very interesting information David. i learned something new today :)

Interesting.
I would like to try this. :)

A large enough mass (wild turkey hen) at about 80 MPH  :o(129kph) will penetrate the windscreen. :P

Can anyone try lead glandes on a windshield?

I've junked quite a few cars and helped others prep a few for demolition derbies.  your unframed 2'x2' specimen is actually quite a bit better at absorbing energy than one that's firmly glued into the frame of a car.  your results woupd likely be very different on an actual vehicle.

Sorta think soap bubble, the larger it is, the weaker it is.  It will also flex a lot more when the rock smacks it, so you will get more cracks but fewer spalls that actually seperate from the plastic.

The only thing I have ever hit my windshield with was a tennis ball from about 50 meters or so, luckily I didn't break it.  I was one of the shooters at various vehicles and types of armor for armoring limos, a normal windshield at a certain angle will deflect .38 Special, 9mm and .45 ACP.  Be in a sportscar, not an SUV if somebody is shooting at you head on.

What I really want to know, though, is how come a BB sized rock can crack my windshield? >:(

Steven wrote on Jun 3^rd, 2013 at 8:55pm:

A large enough mass (wild turkey hen) at about 80 MPH  :o(129kph) will penetrate the windscreen. :P

I think I've got a lot of work to do before I can sling a turkey though.

Cetilim wrote on Jun 4^th, 2013 at 10:05am:

Steven wrote on Jun 3rd, 2013 at 8:55pm: A large enough mass (wild turkey hen) at about 80 MPH  :o(129kph) will penetrate the windscreen. :P I think I've got a lot of work to do before I can sling a turkey though.

That's what a cannon is for.