Been seeing a lot of videos about them breaking glasses in an instant, but i’m clueless to this sorcery. The same glasses take say a conventional hammers/crowbars/screwdrivers multiple tries to break. There’s no source telling how it works and i’ve personally never seen this thing in real life. Why do these hammers have such a small tip and how does it breaks glasses with ust a mild pressure on the window? I get the seatbelt cutting part, but the hammer part is a bit baffling.
Is “f=ma” the right answer to this concept?
Some unusual designs they’re coming in now (tubes) are beyond my comprehension.
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force can be applied slowly or quickly, over a small space or large.
Think of it like laying on a bed of nails. If you lay on a single nail, you’d be in for a bad time. Laying across nails, it equally distributes the weight. For your situation, you want that single point. Also thing of how much force it might take to puncture your skin with a sewing needle vs kabob skewer.
This then brings into question the material properties of glass/windows. They are strong, but brittle. By applying a force to a very small area will compromise the strength easily and therefore break the window.
Lastly, practicality. Sure a sledgehammer can break a car window but how practical is it? they have innovated the tool you’re referencing to the point where it takes up little space, can be easy to use, and have the same intended results.
The important feature of a safety hammer is its hardened tip. The safety glass is hardened glass which are often much harder then regular steel. So if you try to push a regular steel object, like a knife, into the glass then the steel will just bend or mushroom against the hard glass. This spreads the load over a larger surface area so the glass can withstand the force better. However a safety hammer have a hardened tip, it may not be as sharp as a knife so there is no danger of cutting yourself with it. However when the hardened tip hits the hardened glass it will not deform and all the force gets focused on a tiny spot in the glass. This tiny spot is where the glass first cracks. The cracks goes into the glass where it is more brittle and the cracks go through the center of the glass all the way to the edges filling the glass with cracks.
You don’t need a car safety hammer. If you need to crack the window, pull the headrest out and slam one of the metal posts into your window.
Tempered glass is very strong and resistant to impact. The key is though, if it gets even a tiny crack, it catastrophically fails, and the whole thing shatters into tiny peices.
A safety hammer works by having a hard, and very pointy tip. The hardness is key to being able to actually scratch the glass, and the very pointy tip allows to easily crack through, because of physics. The smaller the area of impact is, the greater the force transfered to that point is.
So combine those factors, and you generate a fairly big force in a tiny spot, with a material that is hard enough to chip the glass. The glass then just shatters on its own.
A hammer spreads the impact over a wide area, which can be more easily absorbed by the glass. A safety hammer concentrates the impact at an extremely tiny point. It’s also quite hard, most likely harder than your screwdriver.
For example, put a small thin piece of hardened steel over glass, hit the metal with that safety hammer, and it won’t break. That’s because the metal spread the impact over a larger area on the glass.
Also keep in mind that not every glass in your car is the same
Your windscreen is laminated glass, it will break but not shatter
Your dwindow glass is usually just hardened glass that will shatter
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