# How to knock over a 100 pound domino using a teeny tiny dominoDecember 22, 2014 11:32 AM   Subscribe

If you had to knock over a 100 pound domino with a domino that is 5mm high and 1mm thick (and weighs a few ounces), how would you do it? Give it some thought, perhaps discuss it over a beer, and then enjoy an interesting physics demonstration here.
posted by SpacemanStix (57 comments total) 17 users marked this as a favorite

I heard that Shadowy Men on a Shadowy Planet playing on the video, and thought to myself "that guy must be a Canadian." Indeed, from U of Toronto. Now I want to see a demo with the Empire State Building...
posted by fimbulvetr at 11:41 AM on December 22, 2014 [4 favorites]

It's a good physics demo, but an even better economics demo on the power of compound interest.
posted by Homeboy Trouble at 11:42 AM on December 22, 2014 [9 favorites]

The way that this question was phrased implied "direct contact" to me, so I was thinking about domino railguns with ultrahard-non-ablating 5mm^2 dominos. Ymv^2 may vary!
posted by lalochezia at 11:42 AM on December 22, 2014 [23 favorites]

If you had to knock over a 100 pound domino with a domino that is 5mm high and 1mm thick (and weighs a few ounces)

You know, when you set the problem up that way, it's a bit of a cheat to have an answer which is "use a whole bunch of other dominos!" I mean, I could also answer "hold the little domino in my fist while it pushes the big domino over."

It would be possible, though, within the constrains you give to have the small domino topple the big domino directly; you would just need to construct the dimensions of the big domino in such a way that it was so delicately balanced the slightest tap would knock it over. So there's a physics question for you: just how thin would a 100lb domino need to be to be toppled by a 5mm x 1 mm domino that weighs just a few ounces falling against it?
posted by yoink at 11:44 AM on December 22, 2014 [15 favorites]

It's a good physics demo, but an even better economics demo on the power of compound interest.

There's a commercial airing for an national investment firm that uses this very concept, so I confess that it was the very first thing that came to mind.
posted by muddgirl at 11:45 AM on December 22, 2014

Nah, the trick is to remove the air from the chamber, THEN use the rail gun. No atmosphere, no need to worry about ablation. More fun that way too, as all the little pieces can go everywhere.

I'm deducting points from the video because the demonstrator mixed SI and Imperial units. Millimetres and Pounds. Bah!
posted by YAMWAK at 11:45 AM on December 22, 2014 [6 favorites]

Hah, railgun was my first answer too. Fire it from the side and aim near the base.
posted by Mitrovarr at 11:45 AM on December 22, 2014 [1 favorite]

Yeah, no fair, he's using materials not stated in the problem.

You trade the small domino to the fruit vendor for a small banana. You put the banana atop the large domino. The orangutan knocks over the large domino over while trying to reach the banana. The babel fish flies in your ear.
posted by justkevin at 11:48 AM on December 22, 2014 [26 favorites]

Lift with your legs not your back! Otherwise we're going to be asking how a 5mm domino can create a bulging disk in your spine.
posted by BrotherCaine at 11:51 AM on December 22, 2014 [7 favorites]

You know, when you set the problem up that way, it's a bit of a cheat to have an answer which is "use a whole bunch of other dominos!" I mean, I could also answer "hold the little domino in my fist while it pushes the big domino over."

I wasn't sure how to word it in riddle format without giving it away somehow, but maybe there just wasn't an ideal way to do that. Perhaps I should have said, Using only dominos, how would you... That still would have been half-way interesting, and probably would not give too much away for people who don't have a natural intuition about how this experiment works (I don't think that I would have guessed).
posted by SpacemanStix at 11:52 AM on December 22, 2014

No, silly, you present it to the guy who lives in the giant domino and ask him how to make it collapse.
posted by metaBugs at 11:53 AM on December 22, 2014 [2 favorites]

Glib comments aside, I genuinely like this post. Thanks!
posted by metaBugs at 11:53 AM on December 22, 2014 [2 favorites]

Terribly disappointed we don't get to see the Empire state building sized domino.

(but seriously this a fantastic demonstration. I love physics)
posted by Twain Device at 11:54 AM on December 22, 2014 [1 favorite]

I want to see a domino that's twice as big stop all the ones before it to show that it can.
posted by cjorgensen at 11:55 AM on December 22, 2014

muddgirl: There's a commercial airing for an national investment firm that uses this very concept, so I confess that it was the very first thing that came to mind.

Ditto. Here's the commercial, and a "behind the scenes" video.
posted by filthy light thief at 11:58 AM on December 22, 2014 [2 favorites]

Using these rules I'd just kick off some insane Rube Goldberg device by hitting a tiny switch with the tipped over small domino. 413 steps later if everything went perfectly the 1962 Chrysler 300 would make easy work of the large domino.

I do like the video though and especially the look and sound of the 'dominos' as they fall. I am also waiting for the larger Empire State Building demo video.
posted by Clinging to the Wreckage at 12:00 PM on December 22, 2014

Now I have an urge to recreate this in Minecraft or Gary's Mod, just because.

In KSP, the answer (as always) would be "more boosters."
posted by fifteen schnitzengruben is my limit at 12:02 PM on December 22, 2014 [3 favorites]

How many dominos would it take to have the last one falling destroy the whole planet?
posted by cjorgensen at 12:03 PM on December 22, 2014 [1 favorite]

I'm guessing if 29 is the empire state building, somewhere in the 30s is the earth, eh?
posted by maxwelton at 12:04 PM on December 22, 2014

There is a good intro physics question in this, that asks what the relationship must be between relative masses, big dominoe's dimensions, and place of small dominoe's impact so that the big one falls over and doesn't just absorb the impact. I'm not good at that kind of physics but would enjoy seeing that worked out. Great vid, SpacemanStix.
posted by benito.strauss at 12:08 PM on December 22, 2014

Take a wad of cotton fiber, press it into the shape of a small domino ... I mean, gee, there are SO MANY good valid answers to this question as posed ....
posted by hank at 12:10 PM on December 22, 2014

Regarding compound interest, this is also a good demo of why it takes so long for the non-wealthy to start getting any real effect from their "dominoes" and how by shaving even a fraction of the mass off the top domino you can allow the bottom dominoes to skip a number of interim steps. If each step is a year, and the, say, seventh domino represents "real" money, you can take stuff from the tenth domino that it won't even notice and allow the chain to start from the third or fourth domino instead of the first.

Also, if this is investment income, the floor represents actual day-to-day living expenses. Most people don't even have a domino, in that example.
posted by maxwelton at 12:12 PM on December 22, 2014 [5 favorites]

That guy seemed a little too winded from lifting that big domino. Less calculus, more calisthenics, my friend.
posted by dgaicun at 12:18 PM on December 22, 2014

posted by furtive at 12:19 PM on December 22, 2014

The gentleman has the exact same build my high school science/physics teacher had. Strike that; that ALL of them had.
posted by ReeMonster at 12:21 PM on December 22, 2014 [2 favorites]

You know, when you set the problem up that way, it's a bit of a cheat to have an answer which is "use a whole bunch of other dominos!" I mean, I could also answer "hold the little domino in my fist while it pushes the big domino over."

Well you could still do that, just with dominoes. Put the 5mm domino in between the last two. Just tape it on the front of the domino like so. And that seems just as pointless.
posted by charlie don't surf at 12:21 PM on December 22, 2014 [1 favorite]

I'm guessing if 29 is the empire state building, somewhere in the 30s is the earth, eh?

At the risk of exposing my ineptitude with simple maths, I think a domino the height of the earth is 25.3 steps away from the Empire State Building. Call it 26 to be safe, so Earth would be the 45th domino. (Factoring in gravity (the force) and Gravity (the film plot) are left as exercises for the reader)

(Based on:
Empire State Building is 443m tall including spire.
Earth is 1.257x107m diameter, give or take.
So to find the number of steps, we just find x in `433 * 1.5x = 1.275x107`)
posted by metaBugs at 12:27 PM on December 22, 2014

This video is clearly geared towards people (like me) who think physics is awesome but don't know anything about it. Therefore I can't add to the "Pshaw! You could also do it this way" comments. I can only say what I thought when watching it: "Hey, cool, man! And the first one is so teeny and cute! Wait - the 29th would be the Empire State Building?? No frickin way!"

Great post!
posted by billiebee at 12:31 PM on December 22, 2014 [2 favorites]

Stephen Fry did this on QI, only he used a feather to start off the domino chain.
posted by axiom at 12:42 PM on December 22, 2014 [1 favorite]

Give me a domino small enough and a pivot and I shall move the world.
posted by maxsparber at 12:43 PM on December 22, 2014 [1 favorite]

I'm flashing back to the year I had to explain to my 7 year old son that Dutch TV could no longer afford to produce Domino Day. That was a sad, sad day.
posted by rikschell at 12:53 PM on December 22, 2014

Using these rules I'd just kick off some insane Rube Goldberg device by hitting a tiny switch with the tipped over small domino. 413 steps later if everything went perfectly the 1962 Chrysler 300 would make easy work of the large domino.

The important thing though, is that OK Go would make a really awesome music video out of it.
posted by happyroach at 12:55 PM on December 22, 2014 [1 favorite]

I'm still hung up on the part where a domino can only knock over a domino 1.5x its size. I would think that could be increased significantly if you put the small domino on a raised platform, since the higher from the base you tap a domino, the easier it is to topple it. For this the whole chain would have to be on some stairs. (The slope of the stairs would be constant, like the slope defined by the tops of his dominoes, but the spacing of the steps would increase exponentially with the size of the dominoes.)
posted by aubilenon at 12:59 PM on December 22, 2014 [2 favorites]

I enjoyed this, but had the same initial reaction many upthread seem to have had.

For other fun physics demonstrations, I recommend checking this guy out; Wally Wallington. He claims to have figured out how Stonehenge was built using easy to understand leverage. My father in law busted these videos out when his mother in law, who is a bit of a space cadet but quite fun to talk to, was talking about how the ancient people used levitation to build Stonehenge and the pyramids. I was very thankful.

As far as I can tell, his only mention on the blue was in this AskMe thread.
posted by staccato signals of constant information at 1:05 PM on December 22, 2014 [2 favorites]

a domino that is 5mm high and 1mm thick (and weighs a few ounces)

I'm still trying to figure out what material a domino that small is made of to weigh that much.
posted by fairmettle at 1:11 PM on December 22, 2014 [2 favorites]

That caught my eye too. They probably meant a few grams. But I think even that might be a stretch for such a small domino.
posted by DarkForest at 1:18 PM on December 22, 2014 [1 favorite]

I totally guessed, because he didn't mention it in the video. I think grams is much closer to reality.

If you dropped a domino from the top of the empire state building, could it knock over a 100 pound domino?
posted by SpacemanStix at 1:20 PM on December 22, 2014 [1 favorite]

I was picturing wedging the small domino under the large one until it tipped over. Does that not work?
posted by maryr at 1:34 PM on December 22, 2014

You may get past the 100 lb domino, but beyond that domino is another domino of greater size and ferocity, and beyond him another domino, and so on, until there will be a monolithic domino whose visage is so fearful to gaze upon that such a small and pitiful domino as yourself would surely perish in the attempt.
posted by benzenedream at 1:39 PM on December 22, 2014 [2 favorites]

Thinking about it, you're releasing potential energy as you topple the smaller domino. That's pushing the larger domino, and raising its center of gravity as long as the center of gravity of the larger domino is inside its base - so, doing work and consuming the potential energy released from the smaller domino's fall. Once the lean of the larger domino is large enough, its center of gravity crosses out of the base, and it is unstable and will fall on its own, releasing a much larger amount of potential energy. Draw a line down vertically from the center of a domino to the ground - the goal of the smaller domino is to push this line outside the base of the larger domino, making it unstable.

So really, the 1.5x factor comes from assuming both the density of the dominoes and the relative proportion of height to thickness. If you made the dominoes proportionally thinner, you could get a larger amplification factor, at the cost of more intrinsic instability. In the limit, think of sheets of paper standing on their edges. The tiniest wisp of a scrap of paper could knock over a sheet the size of the Empire State building. The trick would be to get the sheet to stand upright in the first place.
posted by RedOrGreen at 1:47 PM on December 22, 2014 [2 favorites]

Good lord, how many beans does it take to knock over a plate of them?
posted by Celsius1414 at 2:04 PM on December 22, 2014 [1 favorite]

Stephen Fry did this on QI, only he used a feather to start off the domino chain.

To demonstrate how to knock down the Shard with great efficiency.
posted by urbanwhaleshark at 2:17 PM on December 22, 2014

you thought railgun, i was going way more low-tech, imagining using a domino-tipped spear and an atlatl

i really like atlatls
posted by NoraReed at 2:26 PM on December 22, 2014 [1 favorite]

Intriguing. I've built a two-domino solution using a small domino composed entirely of anti-matter. On the pro side, the large domino appears to have been not only knocked over, but almost entirely obliterated (along with two walls and a significant percentage of my workshop's roof). However now my hair is falling out and I feel so very tired all of a sudden.
posted by um at 3:14 PM on December 22, 2014 [1 favorite]

So really, the 1.5x factor comes from assuming both the density of the dominoes and the relative proportion of height to thickness.

The only things that matters about density are: 1) all the dominoes have the same density, 2) they're heavy enough that we can ignore the atmosphere. But the aspect ratio matters a lot. It looks like he's using the proportions of regular actual dominoes, which seems reasonable.
posted by aubilenon at 3:27 PM on December 22, 2014

I'm still trying to figure out what material a domino that small is made of to weigh that much.
Based on the sound they make hitting each other and the machining on the sides of the largest domino, I think it's some form of artificial stone material, something like Caesar Stone.
posted by dg at 3:27 PM on December 22, 2014

"...it weighs about a hundred pounds, and is more than a metre tall..."

/eye twitch
posted by obiwanwasabi at 4:15 PM on December 22, 2014 [2 favorites]

To digress from the scientific points, I LOVE that this was filmed in a university hallway, and he kind of reminded me of Dr. Steve Bruhle. (For your health!)

Yeah I'm in the "Wow this is awesome, that first domino is so teeny! Cool!" camp.
posted by flyingsquirrel at 4:47 PM on December 22, 2014 [1 favorite]

Meanwhile, the Dutch went full Kaiju on their pentultimate domino, which may explain why rikschell had to explain to his kid why they can no longer afford to do a demonstraion on television for Domino Day anymore. "Sorry, kid. They used up all the money to go for the record."
posted by KingEdRa at 4:54 PM on December 22, 2014

Define one and a half times bigger! 1.5x the weight/volume (assuming constant density)? The height? Each of the dimensions individually?
posted by jeather at 7:25 PM on December 22, 2014

SpacemanStix, your username really biased my initial thought process about the question.
posted by halifix at 7:29 PM on December 22, 2014

I'm guessing if 29 is the empire state building, somewhere in the 30s is the earth, eh?

Katamari Dominocy!
posted by BrotherCaine at 8:23 PM on December 22, 2014 [3 favorites]

Isn't this why the U.S. fought war in Korea, Vietnam, Nicaragua, and so many Arab dominoes I loose count?
posted by breadbox at 9:35 PM on December 22, 2014

Gravity amplifier!
posted by chisel at 10:16 PM on December 22, 2014

Define one and a half times bigger! 1.5x the weight/volume (assuming constant density)? The height? Each of the dimensions individually?

Looks like 1.5x each dimension, rather than ∛1.5.

That would predict the smallest domino being about 20mg (100# / ((1.53)12), which is in the ballpark of correct.

If the weight were x1.5, the smallest one would be 350g. Which is clearly not the case.
posted by aubilenon at 2:25 AM on December 23, 2014

Katamari Dominocy!

♫ Katamari Dominocy ♫
posted by SpacemanStix at 8:33 AM on December 23, 2014

♫ Katamari Dominocy ♫

With a touch of ♫Pitagora Suitchi♫
posted by aubilenon at 2:36 PM on December 23, 2014

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