How is a Manu Bomb So Powerful? 

"Did you need the electromagnet to drop the metal ball?" ActionLab: "Yes"

I never knew that the Manu was a thing. I've been doing them for about 35 years, made it up when I was a teenager. I've always amazed all my friends and family at how big of a splash I could make.

There is nothing I love more than the Manu getting the international attention it deserves.

I use to Manu bomb as a kid all the time. My technic was to jump in like you're sitting on a chair, slightly laid back, then when submerged in the water flatten out such that you make a bigger hole for the resulting upward rush for the splash. If you do it correctly, the splash should sound like a loud thud from the shock wave (especially in a pool). This bomb technic is a very Kiwi thing, especially among Maori children.

gotta love a person who can explain science so well, thank you. you make it very easy to understand.

You've just solved an old childhood mystery. My brothers and I would have "highest splash" contests, and sometimes we'd generate HUGE splashes seemingly at random. None of us were able to narrow down exactly what we were doing to make them.

When I was growing up we had two things we did from the high board (3 meter). One was a "cannon ball" which was the same principle as the steel ball. The chubby kids were really good with a cannonball. It also was a way for kids who didn't know how to control their position in mid air to really hurt their backs. The other was a "can opener". This, was a far more effective splash for people that actually knew how to do it. It is basically the same as the "manu". The trick is to lean back as you enter the water. Instead of grabbing your knee at the height of your jump, you wait until just before you reach the water. By bringing one knee up towards your torso your body begins to rotate backwards. Your extended foot pierces the water so that as you flatten your back, the water doesn't slap it as it would in a belly flop. If timed just right you could soak the lifeguard sitting 30 feet away and 10 feet in the air. The most addicting thing about doing this is the intense concussion of water you feel as the bubble collapses around you. A good can-opener rattles your head. You know you did it right if your body abruptly and completely stops moving down through the water just a couple of feet below the surface. You actually hear the concussion like an underwater bomb. "sssSSS-BOOM"

We did these at the public pool. There's two versions. The can opener, which is a cannonball holding one knee only and keeping one leg straight out in front. You have to hit the surface tilted back at about forty degrees. The second was the chair. After springing off the board you a assumed the back lean like the can opener but froze in a seated position with your arms tucked into your sides with your palms covering your eyes. Getting the angle right doesn't take long. You know you did it right when you hear the tremendous thump of the water cavity collapsing underwater.

Interesting. At the pool we would always do a "cannon ball" and make a big splash. But the biggest splash was made by a "can opener". I would jump in feet first, tuck one knee in, and on impact lean back to hear a loud "boom". That's when I knew the splash was really high. Knowing how to control it allowed you to direct it and... make the lifeguard wet.

We used to call it a "Can Opener" The only difference is you grab one knee and pull it tight against your chest while leaving the other leg extended, once your foot of the extended leg touches the water, you wold lean back and continue to fall into the water at an angle. . I remember how it would sound underwater. I never really thought about it but now I know that the sound it created was the void cavatating.

One thing I love about Action Lab is you never know what new topic it’s going to cover. It’s almost always something fascinating that I didn’t know was a thing. And, of course, explained so the physics can be grasped by a non-physicist.

I've seen those videos a bunch of times and I had ideas about how it worked, but wanted to investigate more. And here you are. Thanks man.

This also perfectly explains the toilet splashback bidet effect. Nice work!

The Slow Mo Guys did an amazing experiment inside a wave simulator that has complete round basin that can generate waves from all sides, and they do this, not by dropping in a round object, but to crash precise waves into the center, giving the same effect of a very high jet.

This was a huge thing amongst kids back in the 70s wherever there was something to jump into water ,trees,bridges anything

I worked as a lifeguard in a pool for quite a few years and we were always messing about doing "Bombs" from various diving boards to see who could make the largest splash. Its interesting to see the actual physics behind it.

This should have been called the toilet water jet.

I can remember as a kid growing up my family would visit the Okere Falls near Rotoiti (New Zealand) and there is a place here that all the locals used to jump of a high cliff into the river below where the water was very deep. I took a lot to build the courage to jump this height and at this height you made sure you kept your body straight and upright and hit the water feet first. I can remember one day seeing a group of local Maori teenagers who decided to manu from this jump height.

I used to always make splashes like this but with my hands and they make a really cool sound, a frequency sweep from low to high pitch

As a kid (now 56) my friends and I would do what is called a "jackknife" from the high dive and could aim our splash.....usually at the lifeguard on duty! Same principle, hit the water with your body at about a 45* angle with one leg bent up towards your abdomen held by your hands and when your foot touches the water you quickly lean back to create the same motion and effect as mentioned in this video. Good explanation of what my 12y/o self did so many years ago. Even if the science behind it didn't matter to me before, it brought back a lot of forgotten memories of being young and having some innocent fun. Good video!

I'm amazed he hit the falling ball with the up-shooting water.

You just explained Poseidon's kiss without having to mention it. 😂

I don't think I've even been following James that long, probably a bit over a year, but it seems like the channel has grown MASSIVELY. I don't remember seeing his views go into the tens of millions per video back then! Maybe they were, but either way I'm very happy for his success.

I was just searching action lab videos hoping he already made a vid on it and sure enough he did! Man has vids for everything!!! So grateful 👍🏼

A family friend that used to watch us as kids taught me how to do this and I used to do it all the time. We would just hold onto the ball, not throw it. I also did it all the time with no ball just for the splash. You always knew when you did it perfectly by the sound it made under water, and when there was a bunch of pissed off people when you came up. I never knew it had a name until now.

This looks very similar to the Munroe effect that is used in high-explosive-anti-tank ("HEAT") warheads (hollow charges) to create a very focused and high velocity stream of molten metal to penetrate a tank's armor.

It's amazing how much you can capture with that slow mo camera. It doesn't look like anything without it but MAN does it look cool when slowed down!

Since I was a young boy I’ve done a similar jump called the ‘can opener’ wherein one knee is pulled up to the chest but same body-back motion as the manu. Always gets a huge water jet!

It’s like a shape charge of water

I don't know how you do it... Every video you release is just so interesting and educational. Love it!!

the concept seemed pretty intuitive to me because i often play around with water (anything physics-y) during my swim practice, and i kinda just learned how water behaves in certain conditions

I did a manu once unintentionally once at the public pool while doing a can opener off the high dive. I went what felt like 6 feet deep before the water actually started closing above me, and the splash was enormous. I could never quite figure out how to do it again on purpose, so it was really cool to learn that other people have mastered it!

Even a single piece of toilet tissue laid in the toilet bowl can prevent all undesired splash back from reaching your fundament. The water surface of toilet bowls is small and the depth often shallow so after the first impact, any subsequent stool that goes into freefall is likely to interact with earlier deposits preventing any subsequent jets. No one else (of the admittedly few) with whom I've discussed this has done it so this doesn't appear to be a widespread technique amongst people I know and I am inordinately proud of making this discovery myself. Yet there is a German language term for it translating to "building a raft". It doesn't take a raft though, one square works perfectly and is just that little bit more environmentally and economically friendly. I'm sure others have made their own independent discoveries like me, but it can be a rather awkward thing to share. Maybe someone out there is brave enough to start a social movement about this movement.

Mesmerizing. Very cool to see the close up details, fluid dynamics are wild

Thanks for the video.

We need this as a bigger experiment to go to space!

U make science so easy to understand

I didnt knew that was called a Manu! Sometime in my teenage years i found out you can make a really big splash if you land "sitting" with your legs straight out, and as you hit the water, lay flat fast. Now i know why, thanks!

I just realized during your ball drop experiment that this is a great analogy for what happens during a lightning strike. The initial bolt rips the air apart and creates a cavity in the atmosphere, and when it slams back shut, the "jet" of air it creates is perceived as thunder. I wonder if a literal jet of air is created in the upper atmosphere and if this could have anything to do with sprites, jets and elves (the atmospheric anomalies, not the creatures).

The counter clockwise twist of the rising column is mesmerizing

This explains something that I was intrigued by when I was a kid. Growing up in the tropics, a lot of time was spent staring at the rain drops, and each drop used to throw a larger jet of water into the air as it hit the puddle - I think this is the reason behind that. Thank you!

Amazing physics! I never heard of this Manu but looks like fun!

Looks like something you'd see when watching someone try to finish a video game as fast as possible.

This is also how torpedoes work. Their explosive charge doesn't do the damage itself, it creates an air cavity and the water jet punches through the armor

I’ve enjoyed your videos for years and you have inspired several useful inventions I’ve made. Thank you for all you do!

We used to call this a "cannon ball".

great analysis !

Similar to a manu, as a kid we used to do a "jackknife". You'd jump into the water while holding 1 knee and your other leg extended. As you entered the water, you'd fall backwards letting your extended leg rise above the rest of your body. Made for great splashes. Holding your knee helped to lean back farther and faster for larger splashes.

We called it the coffin, arms crossed, feet first and then as feet enter the water your body, slightly bent, overtakes your feet thereby creating the large cavity mentioned. Also it can cause, if done right, quite a clap noise when the water collapses back. We were quickly banned from doing that due to the noise and the wet ceiling, haha, great fun though, thanks for explaining the mechanics behind it 🙂

This seems closely related to how a shaped charge explosive can penetrate crazy thicknesses of steel plate. It always amazes me how a relatively small diameter hole can keep going and going through a couple feet (or more) of steel, without even "mushrooming" out and dissipating.

When i was a Kid i seen this olympic diver doing a double back manu off a handstand at our town pools..His form was tremedously perfect

I love this guy... Thanks from NZ.

On another note, this is probably why canonballs in naval warfare were quite effective for a long time even if they do not hit the target itself and only lands somewhere near, because then then other than the manu bomb effect, when the water fills up the cavity of impact, it also pulls water from its surroundings disturbing the area where the target is and possibly capsizing it if enough disturbance was made. Now, of course, everyone has deadly missiles.

We used to call that the Jack knife to get that big splash.

Great video. It takes us all back to our childhoods and from around the world too.

I learned something new and unexpected. Nice one!

I've seen others mention it so my vote is for the "Can Opener". But part of the skill was controlling the spray. While sometimes for height, also to spray people standing around the pool. You could get some distance to the back row lounges! And I found a properly performed "belly flop" did not hurt and made a great side splash.

I like how the initial manu creates another manu as it falls back down

ive been making splashes like this since i was a kid and had no idea they had a name or a backstory like this. we called them can openers and just learned than if you hit the water the right way you get a huge splash. cool to learn all of this years now as an adult

So this is what happened when u drop a giant crap in toilet without paper on the surface of water🤔

Crazy that no one ever jumped in the water until someone From New Zealand did it.

My older brother went to a "sports school" in the late 70's, which was actually a camp for troubled kids in Whangarei, New Zealand. Him and a group of his friends would go to Whangarei Falls, a local swimming hole and have competitions to see who could create the biggest splash. They developed many different techniques for creating a "Bomb" the most successful being the one mentioned in this video. The name of that school was Maunu Health Camp.

I like how far up the tank the ball was lifted.

I had no idea there was a name "Manu" for it, but when I was a kid, many decades ago, we used to "bomb" like this for fun. Somehow I doubt anyone in recent memory "invented" it. I suspect people have been doing it for centuries.

I have only known it as a water bomb and it was already well known how to do it when I first learnt and started doing it in the early 70's here in Melbourne Australia! I'm surprised to hear that it was invented in New Zealand..... No date was given as to when it was discovered? The video shows the guy going in backwards, we also could achieve it going in forwards which I believe produced better results, you could actually aim where you wanted the water to end up, the girls unfortunately didn't find it as amusing as we did but it did get their attention! They would always make sure that they knew where you are at all times LoL.... One deliberate splash, lots of apologies and eventually a date.

This channel is underrated and this guy deserves to be in discovery channel

Whoever's reading this, i pray that whatever you're going through gets better and whatever you're struggling with or worrying about is going to be fine and that everyone has a fantastic day! Amen

Can confirm. I remember doing this as a kid ... And adult. There's a variation of it where you run as fast as possible, that creates a very forceful wave.

A bomb that goes a bit higher than a manu is an easy one called the coffin, you jump in feet first but as soon as your feet touch the water you lean back as fast as you can

When I was young, we did "Can Openers". I'm old AF, and sure that technology has improved dramatically since.

Ah I like this dude I always see his shorts so this is cool to watch

I always thought this was why it was called a "cannonball"

Imma try this next year when the pools are open again I’m definitely gonna remember that

I used to swim and dive competitively back in the seventies and I could do what they call a can opener and it would shoot the water straight up just like you described I never know how it worked though thanks for clearing that up looking forward to your next video catch you on the flip side my brother. ✌️

For the most repeatable and forgiving setup, I hit in a tight V and almost immediately try to flatten out, like an backwards parachute. Just trying to slow down as quickly as possible while also entering the water as smoothly as possible. I've done it as a dive while touching my toes and got huge results, but there was less room for error

Growing up in the rural northeastern US, we called that type of cannonball a canopener

Doing a cannonball into the water works really well too especially if you are good at them.

When I was a kid, I was the master of creating a huge splash of water. We always did it from the high dive in an attempt to soak the lifegaurd. When I was a kid, I always called them a "Sleeper" because of when laying back right after entry into the water. Never knew they were actually called a Manu. I was doing this nearly 45-50 years ago!

When we were kids we spent a LOT of time doing this. You straighten out after you hit & go under the water to get the biggest splash. We used to call it 'lay-backs' in Australia.

The pressure & momentum of the water entering the cavity that was caused by the man that jumped in the water produces a vertical splash that launches the ball up.

@The Action Lab >>> Making waves in 2022...😊

We called it a ‘reverse staple’ - mainly started doing it after a few failed staple dives and badly hurting chests 😅

We called it a jackknife, one leg straight the other bent, holding it with your arms, as you enter the water foot first you pivot backwards creating a larger cavity. We used to see who could hit the ceiling of the dock (about 20’ high) by jumping into an empty houseboat slip. Most of us could easily hit the ceiling.

I discovered something like this and was telling someone at work but was looking at the force trying to keep an object down with an airpocket.

70's kids knew this as a Jack Knife

The fusion reactor I'm working on operates on the same principle of inward focused waves.

When I was a kid we used to call it a "can opener"... Performed slightly differently, but generates the same effect.

The creek they are swimming at is Harvey's creek far north queensland. Great place during summer.

Grew up in the east of The Netherlands, we did this all the time when we went swimming. I basically went for the illustrated technique.

In my youth, we called it a “can opener”. It was the same theory, but, the person would cradle one knee with both hands as the water was entered. With practice, the jet of water could be directed at a modest angle. Innocent and dry sun bathers could be soaked from a distance. What fun!

In Oz as a kid we did this as well never called it a Manu it was called the Jerry bomb but I always got a way bigger splash from doing what was called a "Horsie" . Same principle but in reverse, as you're falling you have your stomach pushed forward with your back arched backwards with arms and legs in a parachute free falling position and just before hitting the water you flex in the opposite direction, have your arms and legs hit the water 1st and just as your torso breaks the water, flex your stomach forward again so there is hopefully a pocket of air that is now being compressed even hard into the water. Same principle as having your hand flat and making a splash or cupping your hand and then flattening it out as you hit the water.

We used to call it the "can opener." Whenever we'd go to the pool and people were talking turns on the diving board, and someone pulled out a can of tuna (back then they didn't have the pull tabs) and looked at each friend imploringly when one finally pulled out a metal scissor-esque device, that was a can opener.

I remember people doing something called a "can opener" I think it was that would splash water really high.

We jump in similar way and we call it bomb, but instead of spreading out, you stay curled up to create bigger cavity. One disadvantage is that your head is on top and cavity can colapse on your head with quite a concusive force, but it's realy something special to hear.

We used to do the can opener off the diving board.

We called it a jackknife back in the late 80s. Contests all summer at the community pool.

That sphere falling in water is so much similar to mechanics of accretion disc!

I didn't know what me and my brother were doing has kids was essentially a Manu Bomb. We just called it a "Can Opener". Only difference is we grab one knee with both our hands while the other leg stayed straight. Releasing on impact to achieve that rapid opening of the body. Thanks for showing us he science behind it.

the first time I heard about Manu Bomb. In my childhood we had several types of water bombs. - Brett (board) (very similar to Manu Bomb) - Totenbein (dead leg) (one leg stretched, the other pulled to the chest) - Kopfbombe (head bomb) (as vertical as possible, head first and roll in just before touching the water) - Schwalbe (Swallow) (as horizontal as possible, belly first, just before touching the water pull in arms and leg and then stretch back through)

Now I have to wait all winter to try a manu bomb