Does a Mirror Bend Before it Breaks? Yes. - The Slow Mo Guys

Added: 2026-06-04

[00:00:00]Hello. Welcome back to possibly one of the worst channels on YouTube to fall asleep to. You may remember several years ago, we threw a hammer at a mirror, and I've looked back at that footage many times in complete bewilderment that upon impact, the hammer makes a small ripple in the mirror. Back then, we only had one mirror, so basically one slow-mo attempt. So, I've got a lot more today.

[00:00:23]And a camera that goes much faster.

[00:00:25]Okay, I'm going to start pretty much where we left off. That's 120,000 frames a second.

[00:00:35]So, I think with the first one, I'm just going to Jesus. Hit it in the same way we hit it in the first video. I've got one light either side of the camera here. And then I've got this third light that is almost parallel with the mirror.

[00:00:46]So, hopefully as soon as the mirror cracks, this one will highlight all the edges of the glass that's just cracked.

[00:00:52]Feel free to ignore some of my test shots. Pretend they haven't happened yet. I was originally just wearing this in my test, but glass did hit the ceiling. So, I'm suited up in this flame suit that the legend Adam Savage gave me.

[00:01:06]Just going to give this a right whack and run to the camera within 4 seconds.

[00:01:26]Wa, that is immensely cool. All of the center pieces of glass are rotating outwards. It almost makes the reflection of the hammer get bigger. Similarly to what I noticed last time is that once it gets to a certain point, once the mirror has bent enough, it actually shatters from the point of impact. And the initial circular crack only goes out as far as that ripple got. And then the rest of the glass cracks more sporadically. But that those initial lines coming out of the first impact seem to reach the edge of that ripple in a circle. And once again, even at 120,000 frames a second, almost no footage of the glass propagation. I want to do that again. I'm at 80,000 full res and I've stopped down from 1.5 to f4. So hopefully that moment where all the pieces reflect the hammer will be a bit more in focus.

[00:02:21]That one went into tiny pieces. Did I hit that harder?

[00:02:29]Wa!

[00:02:30]That one broke from a different spot.

[00:02:32]Look at the state of that. Just completely different. I can't really understand why though. It seems like the crack is entirely determined by the position the mirror was in right when it gave way. It kind of like pauses the vibration and cracks. So, even though this one cracked from outside of the impact circle, the cracks still had to follow around the humps, I suppose.

[00:02:57]To my eye, that was more like the second one.

[00:03:05]Wo! Completely different again. It broke from the bottom. That one had the biggest ripple yet. it. I think maybe depending on how hard I hit it determines when the break happens. If the ripple has hit the edge of the glass, then maybe it's more likely to break from the edge to the eye. And most cameras on Earth, both of these cracks would have happened completely simultaneously. But at 80,000 frames a second, they're four frames apart, which is 50 microsconds.

[00:03:38]All right, I finally broke from the middle again.

[00:03:44]>> Yeah, you you can almost completely visualize the like the resonance pattern. It looks similar to one of those cladney plates where you use the sand and you get different patterns depending on the frequency and then that position is locked in by the shatter. So you can almost determine the 3D position of the glass even though we're looking down on it on a 2D plane. In this one, the long cracks are where the mirror was in a lower position, like ball-shaped, and the dense small cracks all tightly packed together is where it was raised in like a hump.

[00:04:14]I think we should up the frame rate.

[00:04:17]I've set it to 640 by 128 in black and white, giving us 875,000 frames a second with a 280. I don't want that, actually. Let's go uh 571 nancond exposure. I've got to be really precise with the point of impact.

[00:04:35]Probably only an inch and a half of height on the entire frame. And I'm going to try and hit it around there.

[00:04:57]Wow.

[00:05:04]Just love filming at these speeds because that one cracked from somewhere else off camera. I think we should try again. Making a right dog's dinner out of this garage.

[00:05:15]>> God, that hit the lens.

[00:05:17]Bit of glass straight in the lens. God.

[00:05:20]Oh, I think this one broke from the hammer spot.

[00:05:26]Wa.

[00:05:28]That is so cool. It's like each point of the edge of that propagation must be the speed of sound through glass, which means that it's a perfect circle. What's crazy to me about this footage is how sharp that front line of the crack is all the way around. Because when we're like 120 or 80,000 frames a second, it looks it looks like a much softer line.

[00:05:51]But I assume it's because the exposure time wasn't short enough. It's just the motion blur of the front of the crack that makes it look like a soft line. And you can only see that when you're getting towards a a seven figure frame rate. I was going to move on to filming this reflecting a grid, but I got really distracted by that shot of all of the glass twisting inwards and magnifying the hammer and shimmering all over the place. So, I've got these Titan tubes, which we last used in the the gallium video. They're not that bright in terms of high speed, but they should, if we're looking directly at the light source, it should be something to see when all the glass is flipping around and spinning.

[00:06:26]But I've noticed that there's only two stable colors because I think the way it shows you other colors is that it's flicking back and forth between different colors. So, it seems only blue and green are usable here, otherwise they'll be flickering like crazy in the slow-mo.

[00:06:53]There's a lot of smaller shock waves that travel much faster than the main impact ripple. The lights make it a lot easier to see that. And you can see in the warping of the lights, you can get a good clue on where the cracks are going to happen based on where the lights get thinner and closer together.

[00:07:10]Footage like this makes me think if we are living in a simulation, it's running on a bloody good PC. I'm just going to wreck one with the uh with the flicker and see what it looks like.

[00:07:27]It's actually kind of cool that it's taking so long to break cuz it really warps some of those colors around. That's pretty psychedelic. I don't know what I'm looking at there. Looks like a glass peacock exploded. I wonder if we should go Titans only. Get these big lights off on this one. I'd be willing to try it.

[00:07:45]Yeah, maybe just the side one for the cracks. Pink.

[00:08:01]Good lord. It's like someone threw a hammer through someone's dream.

[00:08:07]Jeez, that is pretty cool.

[00:08:12]Oh, pretty incredible moments in there.

[00:08:16]Okay, now I'm dropping the hammer onto the mirror, but I'm focusing through the mirror onto the grid behind it.

[00:08:28]On this angle, it's a lot easier to tell the exact moment of impact, and as weird as it sounds, how long the hammer was hitting the mirror for before it broke.

[00:08:35]It's actually quite a long time. Like the hammer dropped down into the mirror significantly. I feel like you would think that the second the hammer hits the mirror, it would be gone, but it's sinking quite deep into the mirror for quite a long time.

[00:09:03]Okay, next up I positioned the I position the camera to the side.

[00:09:20]>> Yeah, you can definitely see the warping at this angle. I just want to try again but slightly opened up to camera so it's a little bit clearer to see the impact.

[00:09:34]I love that something as hard and brittle as a glass mirror looks like the surface of a pond in slow-mo.

[00:09:42]It's crazy how just perceiving time at a different rate kind of changes your entire perception of the physics of the object.

[00:09:52]Well, there we go. I thought that was a very worthwhile revisit. I feel like I saw a ton of stuff that I didn't see last time. Hopefully you enjoyed that video. Make sure you subscribe if you like slow-mo. And a big old thanks to all the names you see here cuz they support us at our highest tier on Patreon. That's also the place you can find extremely high bit rate versions of some of these phantom clips, new and old. Thank you very much for watching.

[00:10:14]See you in a bit. I've swallowed it now.

[00:10:17]I was just chewing it in my mouth. Now it's coming.

[00:10:22]Oh, crumbs.