How fast does glass crack? - The Slow Mo Guys 

Hello everyone. I recommend you watch this one full screen or on a computer so you can see the cracks more clearly. They look bloody tiny on a phone screen! - Gav

So if the earth was made of glass, it would take roundabout four hours till it is completely shattered into pieces.

I don't think shorts were the best clothing option for shattering glass at extremely close range.

Dan just accidently explained how the earth is round

2:44 that flash of light was everything

At 6:00 they debunked the "where's the curve" argument of flat earthers.

i cant be the only who didn’t notice the glass plane at the beginning of the video.

To this day it still takes me a minute to remember that Dan is holding the glass in the beginning.

"what goes Mach 4.2?!" A manhole cover.

Glass should break at the speed of sound through glass. You can look up the speed of sound in glass and find values between 4 to 5 km/second. So why does the glass seem to break at 1/3rd that speed? Well after thinking it over I realized that just like seismic waves during an earthquake there are different types of waves traveling at different speeds! So which sound wave are we observing? The "P" or "primary compression wave" travels fastest at about 4-5km/s in rock like material (glass) and is what is generally used for "speed of sound" but that of course travels far faster than what we see here. The "S" or "secondary shear wave" has a typical speed around 60% of that of P-waves in any given material. Great! but this means the "S" wave velocity is still too fast and cant be the culprit. So that leaves the 3rd type of seismic wave: "surface" or "Rayleigh waves". Rayleigh are a lot like the "wave" produced by taking a tight string and flicking it; making the string tighter makes the wave travel faster. Unfortunately this means that "Rayleigh velocity for a sheet of tempered glass" is not something I can easially look up so I will have to approximate using the equation: v=sqrt((N/m^2)/((kg/m^3)/m) We know that surface of tempered glass has 10,000 psi (~7000N/cm^2) of compression ( leaving the inside under tension). We also know that the density of glass is 2.5g/cm^3. Plugging this into and simplifying the equation I am left with: sqrt(7000N/.0025kg) = 1700m/s which is close to the velocity observed! Now this makes sense since the stress that ultimately caused the glass to break was similar to "flicking" the end of a tight rope. I predict that if you hit the edge of the glass with a hammer (or maybe bullet) so that the "p" wave is causing the glass to fail we should observe a much faster (4.5Km/s) glass breaking velocity.

Love the analysis in this video. Dans description of the curvature of the fractures by considering the pane as a section of larger circle is spot on. Not only is it mathematically/physically correct they, explain it in such a way most people can understand it

A road of glass would finish "cracking" from New York to London in 1 hours and 2 minutes

0:59 when the tea and crumpets is on point

Dan: cracks tons of glass Also Dan: wears shorts

The speed measured here is actually the speed of sound in glass!

"I think it's time to get carried away." The basic principle of this channel.

I am rewatching this video after a while and still didn’t notice the glass

8:08 I think it’s so cool that after all these years they are still mesmerized by what their cameras can do

i love how this channel is just two blokes having some fun with a camera for our enjoyment lmao wholesome af keep it up boys

Dan, "How much can you see?" Gav, "Bloody stupid, this is." Me, "Is that an answer? Sure."

Really cool to see phineas & ferb still doing cool stuff in the backyard after all these years.

Excellent analysis on the failure front.

I've always wondered how fast glass cracked. Now I know. Thank you, Slow-mo Guys.

How fast does glass crack? 12M people: well well then, let’s find out

Watching this on my cracked phone

That intro was beautiful. I noticed Dan holding it but didn’t realize it was glass!

I love how he isn’t scared of breaking the glass while wearing shorts

This is important. PLEASE READ. As a lifelong hands-on glass guy (cutter of up to 1" thick, custom flat glass of all kinds and very much more.) Please know the difference between laminated glass and tempered glass. What you have there is TEMPERED. Break a car windshield vs. side or rear window. Only the windshield is LAMINATED. That being said, this is GREAT!!! I have an old vid I slowed as much as I could (not much) and it was quite interesting. Three layers of glass laminated together, the center one being tempered. Installed it in a restaurant, then purposely broke the tempered piece. We call it Crackle Glass. The speed at which tempered glass breaks has always been something I wondered about. THANK YOU! I'd like to see you do pretty much the same experiment with all different thicknesses and compare the speed.

4:34 companies 0.001 seconds after pride month ends

I didnt notice the glass in the beginning lmao

When I watched it, I never saw the glass at the beginning, but after its revealed, I can't stop noticing it.

The famous wasp-filled ceiling fan! I love going back to the older videos and seeing stuff that Gav has mentioned on F**kface!

0:20 I didn't realize anything was there till they pointed it out. That's one clear piece of glass

Who else didn’t notice the glass pane Dan was holding until they mentioned it at 0:24?

5:25 So basically a Square glass that's 1km^2 wide would take under 1 second to fully shatter. Impressive

1:54 that sound though...

The only RU-vidrs I can’t get mad at for taking forever to upload.

Might be one of the nicest videos, visually, ever made on RU-vid. The edits, cuts, little moments... Brilliant video.

7:26 I just wanted a little nostalgia. I wanted none, *zero* reminders of the present day. But to be honest, I probably wouldn’t have minded one much. But this *specific* reminder, these specific colours, will be the death of me.

Gav and Dan: Have an ultra high speed camera probably capable of shooting at speeds of over 50,000 fps, amazing technology at their fingertips. Also Gav and Dan: Glass is cool.

2:10 The ice after Scrat places his acorn in the Ice Age movies

Not as fast as RU-vid rewind dislike rate

14.1 million subscribers, 14.1 million views. The ultimate in efficiency

Loved this one guys, new to your channel and really have enjoyed all I have seen.

Not gonna lie, I didn’t even see the glass until they pointed it out

it's a circle because it's literally just a "sound" wave moving through the glass. the speed at which it breaks is the speed of sound through that material. typically at ~345m/s through air at sea level, the speed of sound is magnitudes faster through solid objects. (audio engineering is a hobby of mine - i obsess over this stuff) amazing video. i loved every second.

Fresh comment for an old post.You guys are doin great things,SCIENCE and stuff MANG!

Excellent video. Excellent maths. Phenomenal speed. Well done, thanks 👍👍

0:33 I legit didn’t even know he was holding glass

"I'm gonna bung in a ton of shutter here. 45 degrees?" - "Ooh, that's naughty! You never do that" "Bloody naughty innit." Love these guys.

I love these guys so much

The guys break glasses out loud. Neighbours: Omg, that family must be having a messy divorce

Just like to point out he’s breaking big pieces of glass in shorts

"Got a church window?" is one of my favorite lines ever on this channel

The circle theory makes so much sense therefore showing how genius u guys r

That was soooooo satisfying to watch the paint just,well,crack I guess

I love that this channel made me actually enjoy learning and it’s just 2 dudes painting rainbows on things and breaking them (for science)

So we can all agree you guys now have to make a giant round glass video.

I’d love to see you guys revisit this with the faster phantoms that are now available.

Did anyone else not even notice the glass in Dan's hand at the beginning until he said "oh here's one!"

6:04 I think that was the smartest thing I've ever heard Dan say in a video

me: "Should i google what that number is in meters?... nah.." Gav: "And for the International audience" me again: "nice."

You're getting a thumbs up from me for catering for your international audience

I literally didn't even see the glass in the intro until Dan grabbed it.

You guys should film macro shots of insects walking and there joints moving, like a ant or a centipede. I think that would look cool.

I didn’t realize he was holding glass in the intro...

one of the best channels

"45°" "Ohh that's naughty u never do that!" "Bloody naughty innit" Best lines

*_Not that fast compared to 2018 youtube rewind disliker growth_*

You should try to fire a bullet at the same time and then compare the speed of the bullet with the speed of the breaking glass ;)

Awesome. It's amazing how fast it goes

Objects tearing apart (glass breaking, balloon popping etc.) are some of the most interesting stuff to slow down, since somehow they go so incredibly fast.

Can you guys do candle wax drop on water really curious how they form in slow mo

I honestly didn't see the glass at first

There are several air/space craft that could outrun glass shattering. That’s so fascinating to me.

The slow mo guys: what goe’s faster than mach4.2 Me:light

Am I the only one who didn’t notice the glass Dan was holding at the start until they pointed it out? 😂😂😂

If i was your neighbor, i would build a deck so i could just watch you guys do your stuff. better than tv.

Love you guys

Hi, Dav & Gun ur all the creativity is awesum

Dan, you probably should have worn some pants for that...

I didn’t even notice the glass Dan was holding at the start of the video.

What a breakthrough!

When you two put a video on you tube there is no point in there being a thumbs down button because all of your videos are great!

I want a video showing how fast two liquid droplets will join surface tension and become one drop. You could do them two different colors.

Lol who else didnt notice dan was even holding the glass???

That was fantastic!

I love how Slo Mo Guys Gavin and Achievement Hunter Gavin are almost complete opposites, and yet cause equal amounts of broken glass.

Btw. How’s that 14 ft glass circle coming

To show the circular pattern that Dan is talking about, shoot a BB at the center of a square piece of glass, and you will see how the circle grows larger. This is the same effect you saw on the rectangular pieces, albeit on a much more limited field if vision.

This is addictive.

7:57 Gav: “it just looks like a software wipe” Dan: “it just instantly turns to like lizard skin”

5:46 Questions: 1) Could the crack propagation have been altered by the thin coat of paint over the glass which lends it a bit of integrity? 2) The Mach number is a useful layman's yardstick but the speed of sound in glass must be different from the speed of sound in air, and you might have drawn attention to that fact. It would not be a surprise to learn that said speed of sound in glass is in fact equal to the crack propagation rate.

Am so thankful that you give the speed in Mach

Amazing guys!!!!

0:21 I did not notice that glass XD

Not as fast as my self esteem broke

WOW!!!!!!! i didnt even see that pane of glass till you moved it. nice optical illusion.

Yep, really liked that. Very interesting. You got a like.

Hey guys, I hope you end up reading this as I have a quite relevant suggestion. As far as I know, a crack propagates through the material at the speed of sound in that material. I googled the speed of sound of glass before seeing the results (about 4500 m/s) and was surprised to see the crack was far slower. However you used laminated glass which uses a thermoplast to reinforce the glass. I also looked for those and the speeds of sound in various thermoplasts is in the ballpark 1000-2500 m/s. I expect the fact that it is laminated glass slows the crack. It would be really cool if you tried 'pure' glass as well and see if the crack is three times as fast as I expect. Otherwise cheers nice video!