Does glass break faster than a bullet? [video] | Hacker News Reader

Does glass break faster than a bullet? [video]

youtube.com

135 pointsmfrw73 comments

For your convenience, the answer is "yes", and this is the timestamp where you can see them race: https://www.youtube.com/watch?v=TAO1i9Z9GpQ&t=162s

As always, the good stuff starts 1/3 of the way through any given video (:

I remember someone stating that "rule" at one point, but not sure if there's an official name for it.

As others have said, the Wadworth Constant. You used to be able to add &wadsworth=1 to any youtube url and it would automatically skip ahead. They got rid of it at some point though.

If you find yourself constantly searching for highlights, I highly recommend the SponsorBlock extension (https://sponsor.ajay.app/), which crowdsources this job effectively (as well as targeting sponsored regions, credits, etc.)

Using the extension I could hit "return" to jump to results at 5:28.

You can press 3 on the keyboard to skip 30% of the way in, it's a reasonable approximation.

That's a pretty slow bullet (I'm assuming it's a spicy 9mm). It should be possible to load rifle cartridges that are fast enough to make the race interesting.

I'd try the Weatherby .220 Swift but I think it'd still lose to the glass. The 120mm smoothbore main gun on the M-1 Abrams tank fires a depleted-uranium penetrator rod that can get near 6000 ft/sec. That'd win.

There's a link in the video to one where they compare different projectile speeds - up to, iirc, a 50cal

Wadsworth Constant, I believe.

i know what you mean about "good stuff", but i did really enjoy the full commentary on this one. you have to give the narrative a chance and you can choose to skip right ahead if you want to without so much of an effort.

The Wadsworth Constant.

Awesome video -- pretty low on fluff compared to how bad YT can get these days, which is a pleasant surprise.

I totally understand the physics and reality of sound/light/etc. traveling different speeds in different mediums, but it's always such a wild thought to me. It tickles my brain in such a delightful way.

For anyone who doesn't want to watch an 8 minute video, the glass / bullet race is at 2:40.

Maybe it's low fluff relative to other YouTube videos, for me it could have been a 5 second GIF without any real loss.

Some want education. Some want entertainment. Some want some wrapped in some.

Sometimes.

This is less about "customer demand" and more about having to meet minimum video length for mid-clip monetization slots. Strictly an artifact of how YouTube works.

I didn't know, I pay the Premium to hide that stuff. Regardless, given the effort and lengths they went to, I'm happy to see them do so in a manner that funds their ability to do more.

YouTube know what they are doing… irritate the hell out of you until you buy Premium.

I once had YouTube on in the background and an advert which was an hour long popped up - but I was focused on something else and away from the screen and the tv remote.

The advert? A video of someone pointing a camera outside of a window during the night and onto a dark street (no sounds other than rustling from the person holding the camera). An hour long of it.

Skip.

It was soon after this I paid up.

You ... rewarded this behavior instead of installing ublock origin and never seeing another YouTube ad?

I’ve seen some doing 10 second previews of action parts and then proceed to setup and education. Too bad platforms encourage them to make you watch a couple of minutes of things that you may not be interested in at the time.

It’s interesting that people complain about vapid reels/TikTok, while also hating on medium-length educational content.

given that (in physics) sound is vibration, I think a clearer way of phrasing it is that glass cracks at the speed at which a vibration can travel through it. glass is much denser than air, so the particles can knock into each other more easily, meaning that the speed of sound (or vibration) in glass is a lot faster

(this isn’t aimed at explaining it to you, just to write out my thoughts, as I found their explanation a little odd)

They made it to that explanation in the video eventually.

fair enough. I didn’t quite make it to the end

Related, hitting a Prince Rupert's drop with a bullet: https://youtu.be/F3FkAUbetWU?t=104

TLDW: The bullet shatters and the drop stays intact.

I wonder what the results would be if done with a steel core/AP type rifle round , the bullet in the video appears to be jacketed plain lead at pistol velocities.

The same channel did a follow-up with rifles here: https://www.youtube.com/watch?v=k5MORochIDw

The difference in muzzle energy from a .38 special revolver and a mini-14 (5.56 NATO with an 18.5" barrel) is so high, it's not surprising.

For sure some very different results but it looks like they're using low cost jacketed plain soft lead. I wonder what the results would be with an M855A1 (available to civilians) or real armor penetrating designed round.

https://smallarmssolutions.com/home/the-m855a1

I’m surprised the fragments didn’t cause the whole thing to shatter when they came into contact with the tail

They describe (at 2:19) that they annealed the tail to remove the tension allowing it to stay intact.

So we should make body armor out of Prince Rupert drops?

Body armour dissipates lots of the bullet energy in the act of breaking. Prince Rupert drop armour would mostly result in the bullet snookering a glass chunk into you instead. Even if you could make a solid glass plate that wouldn't break when shot (doubtful), the transmitted energy of a bullet would still be more damaging because it would all end up in your body, not in heating up the broken shards of a ceramic plate.

The transmitted energy does end in your body in case of normal bulletproof vest tho. Only very little is converted into heat, the main job is to spread it around. Movies as usual do a terrible job of portraying reality here.

Ceramics aren't used because they break on impact, they are used because they are harder per kg than steel so the whole thing can be lighter.

Imaginary "unbreakable plate" would still be backed by layers designed to slow down the pulse and dissipate that energy and if it was thinner and lighter than ceramics that means you can put more materials behind it and still come out ahead

Disagree. People regularly absorb blows with more energy than a bullet without injury.

For those downvoting this, remember that firing a bullet has exactly the same impact on the hand holding the gun.

The same impulse (force times time), not the same energy.

Only the head of the Prince Rupert drop is tough, due to high levels of stress in the glass (its made by dripping viscous melted glass into water). Interestingly, the whole drop with shatter into glass dust if the filament like tail is broken!

Wikipedia has a good description of this. [1]

[1] https://en.wikipedia.org/wiki/Prince_Rupert's_drop

The glass broke by first spreading cracks through the glass, then seemingly simultaneously shards flew apart from the whole glass. I'm curious what accounts for the sharding part appearing simultaneous. Why didn't the sharding process start on one end and travel through the glass?

That was a piece of tempered glass, as we can tell due to the way it broke into tiny pieces. Due to the tempering process, where it's heated then quenched by large fans, the glass is under stress that's concentrated at the edges, and especially the corners.

This is why it explodes when they break the edge the way they did. Ordinary annealed glass would've broken into large, sharp shards, whereas laminated glass would form a break pattern like annealed, but would stay in one piece due to being attached to the plastic inner layer.

They speed up the second part of the video. The "flying apart" bit happens at much lower speeds and would be boring to watch in extreme slow-motion.

I watch slow mo guys pretty religiously. Their other video on bullets and glass was also a fun one - they shot through a bunch of glass panes and it only penetrated like 11 sheets of regular glass. I thought that was interesting.

Their second channel goes into some of the equipment and behind-the-scenes stuff, an interesting one is showing off their file server for the raw video files, 960 TB worth in a small rack-mount unit.. incredible how much data these high-speed cameras produce.

https://www.youtube.com/watch?v=JHVSoJDZ06U ("Unboxing a petabyte")

Handgun rounds are really quite slow - now do it with a 5.56 NATO 55 grain FMJ from a 20" barrel at 3000+ feet per second.

Basic rifle chronographs are under $200 and high enough Hz precision to measure feet-per-second of different rounds accurately. You still can't see it and differences are imperceptible to human senses, but chronographs/chronometers are a heck of a lot cheaper than a super-slow-motion camera.

Commonly used for people testing out different combinations of things for long range precision target shooting.

https://www.snipercountry.com/best-shooting-chronograph-revi...

They clocked the glass at ~3,000 mph so it'd be a lot closer with 5.56 being ~2,000 mph. The fastest production bullet I believe is .270 Swift which is over 4,000 fps depending on barrel and conditions.

Pick consistent units!

Getting Americans to not use measurements like grains (for powder loads or bullet weights), feet per second, yards, MOA, cartridge dimensions and chamber dimensions and barrel sizes in inch-based measurements and other non-metric measurements for anything rifle related is unlikely to happen anytime soon. Unfortunately.

Even things which happen in supposedly entirely metric countries in Europe/NATO land use USA-spec things. Such as: Oh, you want to replace a barrel on your M4 rifle used by a European military? Time to get out your half inch square-drive socket torque wrench and torque that barrel to a certain value in foot-pounds... And after you're done you get to mess around with your SAE spec hex key set to reinstall the hand guard and associated stuff. I'm not kidding.

I was referring to the use of MPH (which is probably wrong) and FPS mixed together.

I don't care about bullet caliber being mixed mm and inch - I consider them to just be "a size" and not a measurement.

> I consider them to just be "a size" and not a measurement.

You're right to consider it that way. In many cases, bullets aren't actually the size the name would suggest. For instance, .380 ACP is actually .355 inches (9mm) in diameter. 5.56x45mm is actually 5.7mm.

MPH is how they clocked it in the video. I should have converted it to FPS because that's the proper measurement for these sorts of things although I prefer or meters per second.

Isn't it just a constant ratio in either case? 1 mph === 1.46667 fps

So? All units of a given quantity differ by just a constant factor [ignoring the affine units °C and °F]. But mixing mph and fps is just as disingenuous as, say, mixing mph and km/h. Nobody on Earth outside the US has any idea or intuition what the conversion factor between mph and fps is.

Disingenuous was not the goal. I was in a hurry and didn't convert the last unit FPS after looking up the specifics.

You've nothing to apologize for. MPH and FPS are both simple distance versus time measurements, both imperial, and trivially converted. Of course it's some non-US individual that has to complain about it, those are the only people who truly seem to care about what units are customary in the US. The rest of us just convert as necessary. Hell, just google search and have the answer in two seconds.

Don't be ridiculous. It would be just as silly to have velocities in both m/s and km/h in a same paragraph. And many, many more people in the world know the conversion factor between those than between mph and fps. It's pretty bold of you to talk about 4% of the world's population as "the rest of us", but unfortunately it's to be expected from a certain type of American.

Vs. those darn limeys, where you just have to know that a QF 17-pounder is a WWII anti-tank gun, but a QF 18-pounder is a WWI field artillery piece...

> like grains (for powder loads or bullet weights)

or heroin

4000 fps ~= 2800 mph

The .22 Eargesplitten Loudenboomer was designed to hit 5000 fps (3400mph), but testing the round most people agreed it only hit 4600 (Just a few dozen mph shy of glass). With modern propellants it would probably beat the glass.

https://en.m.wikipedia.org/wiki/.22_Eargesplitten_Loudenboom... (emphasis added):

> This humorously named cartridge was developed in the 1960s by P.O. Ackley for Bob Hutton of Guns & Ammo magazine, and was intended solely to exceed 5,000 ft/s (1,500 m/s) muzzle velocity. Ackley's loads only managed 4,600 ft/s (1,400 m/s)(Mach 4.2), firing a 50-grain (3.2 g) bullet. Based on a .378 Weatherby Magnum case, the case is impractically over-capacity for the bore diameter, and so the cartridge remains a curiosity. The advent of new slower-burning smokeless powders may have changed the equation.

Oh wow, this is cool. I'd never heard of this round before. I imagine you'd need a very large barrel to burn up all that powder before the bullet left the chamber.

An interesting new material

https://scitechdaily.com/ground-breaking-new-shock-absorbing...

I wonder how the speed of glass crack travel compares to the speed of sound in that particular kind of glass, and if the deficit can be accounted for by the fact that the cracks are not traveling in a straight line.

The shockwave (which travels ahead of the cracks) travels at the speed of sound of the material.

I'd hazard a guess the shockwave propagates about twice as fast as the cracks.

The shockwave is probably at a constant distance from the cracks (AKA, the same speed). If it gets too far ahead, it will just create another crack, in an independent direction, and you get one of those random curves you get on the crack.

That's a fine guess, and it's not like I know any better, but if the fronts don't travel at the same speeds then... why? If there's enough kinetic energy to break the bonds in the material, what's it doing before they break?

The cracks don't travel in a straight line the shockwave does. That's it.

Speed of sound can be literally thought of as the speed that force propagates in a material.

> Speed of sound can be literally thought of as the speed that force propagates in a material.

A.K.A. speed of mechanical causality

apparently there is a bullet that will go nearly as fast as (still slower) https://en.wikipedia.org/wiki/.220_Swift

The .22 Eargesplitten Loudenboomer could probably do it with modern propellant

When I googled that I was 80% confident that you were trolling me and I was falling for it. Nope.

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