"there, there, there, there.....oh dear, it's getting a bit too violent for me."

For those of you asking about swings with rigid bars rather than flexible chains, see the "extra footage" here: kzfaq.info/get/bejne/m79dhrp5sqnFm40.html

Neat how every kid knows exactly what to do when they get on a swing without knowing why it works, until now of course. (And by kid I mean me. :))

"Oh dear, it's getting a bit to violent for me." Priceless!

Loved this. What are the chances of getting all the professors to do their talks while on a swing in the future? :)

Well, pretty sure that shortening pendulum is not main reason to increase amplitude of swing. Proof? On rigid bar swing you can use same motion to increase amplitude, and not only by doing sit-ups like professor said in extra footage video. Also, you can switch position when swing is at maximum positions, and that shouldn't work if shortening pendulum was main driving force. I think swing works by shifting center of mass behind chair when moving forward, and in front of when moving backward. And because pendulum _center of mass_ is reaching same height on both ends (ignoring air resistance), when you shift center of mass behind and in front of chair, you make chair go higher during each oscillation.

Very interesting, as always! Keep up the good job, can't wait for the next video!

PROOF that even scientists and filmmakers can't resist swinging on a nice day. one of my friends used to live on a farm and they had a swing in a big oak tree, was about 60 feet tall. it was equal parts awesome and scary when you got it going good. would take like 7 seconds just to swing from one side to the other.

Excellent point highlighting the shortening chain contributing to a swing's acceleration. But there's a lot more to swing acceleration and momentum than just a shortening and lengthening chain.

I'm so glad to see Professor Bowley is still making videos!

Such a great video and demonstration.... love the passion this person has and how that passion pulls the listener-watcher into learning something new. If I had teachers like him - I’d be a scientist today lol

I'm quite certain that this explanation is missing a significant part of the actual physics. When you lean backward, you are not only applying some shift to the *height* of the centre of gravity, but you are also shifting the centre of gravity out of the plane of the swing itself. To imagine what I believe is going on, imagine a pendulum with a rigid bar. You set it swinging, it goes back and forth, great. Now, with it stationary, imagine that you take another metal bar and attach it to the bottom end of the pendulum at right angles, so that it sticks out to the side, say to the right. When you release this, the pendulum will swing to the left, because that allows the *new* centre of mass to be closer to the ground than with the pendulum vertical. Similarly, if the bar sticks out to the left, the pendulum will swing to the right to accommodate. Imagine, then, a system whereby you could instantaneously change which side the metal bar was on right at the apex of each swing. You start out at rest with the pendulum straight up and down, and the metal bar sticks out to the right. The pendulum swings to the left. In fact, it swings *past* the point of equilibrium thanks to the momentum it gains. Just as it is turning around to swing back the other way (it would eventually return to the starting point, of course), you switch the metal bar to stick out the left side of the pendulum. Now you're imparting acceleration to the right, and it will go substantially further than the starting point. Again, when it turns around, move the weight to hang off to the right, and you'll swing further than the previous apex on the left. I believe this is the true explanation of what's going on, because I've found myself that if you *reverse* the usual process for swinging, and lean back when you're forward and forward when you're back, you actually decelerate the swinging. To make an analogy back to the simplified pendulum in the previous paragraph, then, normally what you're doing at the apex of each swing is shifting the centre of gravity so that the pendulum's rest point is on the *other* side of the Y axis. If you do it backwards, though, you're putting the centre of gravity on the *same* side of the Y axis, so that the pendulum wants to come to rest on the side you're already on and doesn't swing as far on the opposite side.

Marvelous explanation! Thank you very much professor!

I smiled way too much when he was playing with the swings.

I love Professor Bowley's videos, he's so much fun! :-) Eagerly awaiting more sixty symbols videos - wish they were more frequent! About the swing - I thought that moving your feet outward caused some force like when you throw a ball, but your feet are attached to you and so they pull on you, outwards, a little bit, making you swing higher... Something like that.

Finally! Make more sixty symbols videos, please Brady!

Glad to see Professor Bowley again, I was worried we wouldn't get any more videos with him since he retired.

Great explanation. Thanks prof bowley

What about swings with rigid supports instead of chains?

Look at that passion! WOW! for such an old professor playing on a swing with such passion! This is what physics can do to people

Fantastic video

I've often wondered how swings operate. This is amazing!!!

But professor, this same technique with the body and legs in a sitting position works with a swing with rigid bars too! I spent my childhood on such swings. in your explanation you say that you should shorten the pendulum at the mid point, but wen you swing you make changes only on the end points. Surely your interpretation of the dynamics of the swing should be wrong! I think the reason this works is not the changing length but that this motion changes the height of your center of mass. So in the back end point you put your body back, but your seat is tilted, so your center of mass is going actually higher in respect of the ground. Then in the front end position, your center of mass is really below the seat, so you tilt forward and effectively bringing the center of mass higher than the end point, You are pumping more energy in the swing system by adding a little bit of potential energy on the high points. Try it out on a rigid bars swing, you'll sea it's more clear what's going on. With the chain swing you basically have 2 connected pendulums and you know how unpredictable are those.

A great video. Thank you

Great video. "Parametric resonance." I'm totally gonna own the playground now! Now I /know/ I'm not the only one who would've liked to stop the Carlsberg (how do you say it in Britain) "lorry" at 5:00 and carry off a quick pint, eh?! Well, if I won the lottery, I would come to the UK and redo my undergrad experience at the University of Nottingham...gosh it seems like such a fun place to learn! Thank heaven for KZfaq and Brady to give me the next best!

This was great, thank you!

This method works (mostly) because of the angular momentum added when changing the body angle. The one that shortens the pendulum length requires standing on the swing (as in the extra footage).

Awesome video guys stuff like this is why I always love physics class its so fun to learn how the universe works even if its as simple as a swing

There's something missing in this conjecture. My grandfather built me a swing with rigid bars many years ago, and I could swing past the horitontal point more easily than on swings with chains, using the same sitting and rocking technique shown in the main video.

I thought Professor Bowley retired. So happy to see him again! :D

I'm not sure if this is the only explanation. It is also possible to explain the swinging via the conservance of angular momentum: When being at the highest point, you rotate your upper body and legs. This angular momentum is transferred to the swing itself and lifts you up a little more. When being on the other end, you create the angular momentum in the other direction and lift yourself up a little more. Would be interesting to check it on a swing with rigid bars...

This video is hysterical! :D

More professor Bowley. He is a legend!

I bet people driving by were wondering "Why is that man videoing an old guy trying to swing??"

This is awesome

Roger always gets to do the more physical/strenuous experiments. hilarious and impressive at the same time. cheers to the Emeritus! :)

I always thought it was the leg swinging which made you go faster. This has been enlightening!

Finally an answer to the question I was asking myself again and again. There was no good explanation on youtube so far.

If you are also swinging your legs forward, you're obviously also adding energy from your muscles. You swing your legs and then they suddenly stop when straight. That energy goes toward lifting you up, just like when you jump. So, you reduce the weight while going upward, but then it stays while going downward. That has to add a lot to the overall movement.

That's awesome. You got to love learning the science of seemingly mundane everyday things.

I thought he had retired? It's nice to see him again, a great teacher.

You've just inspired a new inquiry lab for my physics students this fall...

Props to the Professor (?) for laboring for science!

I spent my entire childhood trying to figure this out... I never could.... thankyou

the length of the pendulum determines its period or speed. in the center of the swing, bringing the center of mass closer to the pivot point, you effectively make the pendulum shorter so it moves faster. but at the extremes of the swing you effectively make the pendulum longer and slow it down. why that amplifies the effect rather than cancelling it out interests me.

In addition to the bending of the chain by leaning backwards, the rearward lean shift the centre of mass further rearwards and forms an additional moment triangle.

Professor Bowley may think he's 'old'. But he's got the enthusiasm and curiosity of a 12-year-old. In that regard, he is actually very young.

THOSE SLOW MOTION SHOTS WERE SICK

4:53 The most subtle product placement ever.

Hello! I think that rather the bending of the chain, it is the position one takes when swinging that closes and moves away the center of mass of the system to the pivot point: if bent backwards the center of mass is further away from the pivot point than if one sits in the direction of the chain.

Fascinating!! :D

Hi, when i was a kid, here in Poland we've got only rigid bars. And both methods works. Yes, standing works a bit better, and was a faster way to swing as hell, but sitting version still works. So i think, there is additional factor, wich allow me to swinging using both techniques on rigid bars device ;)

For the first time, you guys got it wrong. With the sitting swing, you only change position on the sides and remain still during the whole swing. On the other hand, with the lab experiment you pull mass up in the middle, and let it go down on the sides. The sitting swing works based on a totally different mechanism, than the lab experiment. I'm not sure how to explain it in English. However, when you stand on the swing, you can take advantage both mechanisms ;-)

In the pendulum you change the length of the rope. But in the swing I reckon the change in the center of mass's position changes the length of the rope thereby causing synchronization and amplifying the ampltitude of the oscillation.

The lifting and resting of ones legs also lends itself to the shifting of one's center of gravity upward and downward.

Circque du soleil uses this all the time and its incredible what heights they can reach

Er...two things: 1) That ain't how I remember it (remembering about, oh, 45 years ago or so): One had the distinct idea that it was pumping with legs, and laying out (which could change length of center of mass) that got a swing moving higher. 2) This is a good demonstration of the tendency toward "over-theorizing" in physics. The video would have been MUCH more interesting with some visits to playgrounds -- and experimental cooperation with youthful, show-off swingers. But...theoretical physicists don't really like experiments... I would like to see some enthusiastic kids trying a) to rise high as fast as they could, b) rise high as fast as they could, while being sure NOT to bend the chains. Then we might find out something about how people REALLY use physics to swing.

The slow motion really was a nice touch.

Epic!

Actually there is another explanation for this swing video (not contradictory to the video, just different). Straightening of the legs when seated adds momentum to the swing in the direction of its motion, so net momentum is increased making the swing swing further. Standing up when the swing is at the bottom increases the potential energy of the swing from 0 to some positive number, so this extra potential energy is added to the potential energy converted from swings kinetic energy increasing total energy.

I knew the comments on this vid would be a riot, youtube you do not dissapoint

Conservation of angular momentum maybe? I always wondered how that worked and this video seemed a really nice point to fit in it... Really surprised that it isn't (unless I'm wrong and it has nothing to do with angular momentum)

"Oh dear, it's getting a bit too violent for me." XD :3

I don't think that this is the main mechanism that keeps the swing going. You are rotating your body from legs forward, torso back, to legs back, torso forward and back again. A torque is required to do this, which you apply with your arms. Of course you apply an opposite torque to the swing as you do this. Given that as your body goes back your legs come up, I can't see that there is much change in the position of the centre of gravity.

I want a go!

When I was a kid I had to research how a swing worked before I could do it. Same with skateboarding tricks. This was in the early 90's before looking stuff up was as easy as google is now.

Also worth noting that shortening the string when the swing speed is at maximum moves the mass closer to the rotation point.... the mass is travelling at speed X over distance Y. Distance is still the same, but it is now closer to the centre of rotation, and Y subtends a larger arc, so the swing rate increases.. Conservation of angular momentum?

Is there any relationship between the shortening / speeding up seen in this video and the shortening / speeding up of planets in orbit? i.e.- is swing motion also described by calculus? Don't hate me if I'm wrong as I'm not overly educated in the classical sense - just asking a question!

Parametric resonance: This is how some fly fishermen get very long casts. It's called a double-haul. Check it out. Learn the Double Haul fly cast with John Duncan from Telluride Outside.wmv

lol "It's getting a little too violent for me". Classic.

But how about swings with rigid bars?

Great stuff but I don't know about anyone else but I could do with a bit more Prof Ed Copeland and the kind of physics he talks about - he thinks about the world in ways that just blow my mind!

5:00 That calls for a Carlsberg! Cheers :)

You have the wrong link associated with clicking the "Slow Motion" clip, it send you to the Extra Footage video. The links in the description work, but not the link in the image.

Funny enough, the people at the Santiago de Compostela cathedral knew about this many centuries ago. They did not have swings (not in the way seen in the video at least) and it was not exactly for fun (but for masking the smell of too many people, mostly pilgrims inside the building, which were even allowed to sleep there back in the Middle Ages...), and it's quite sure they didn't know about centripetal/centrifugal forces the way we do today... but there you have the "botafumeiro", which you can still watch live a dozen of times a year. Just a quick search and you'll know what I mean.

So by bending the chains your essentially shortening the distance between the pivot and the center mass and that allows for gravity to accelerate you downward longer than if you didnt bend the chains which is then converted into forward momentum via the pivot?

this solves my question that i had for swing sine i was a child... thank you...

From what I can see, the change in the center of gravity has a much larger effect than the shortening of the effective chain-length. He goes from an upright sitting position to almost laying down on his seat periodically, that's bound to have a much larger effect on his swing.

How to solve this? A child's swing has natural frequency of 0.90Hz a) What is the separation between possible energy values (in joules)? b) If the swing reaches its a vertical height of 45cm above its lowest point and has mass of 20kg (including the child), what is the value of the quantum number n? c) what is the fractional charge in energy between levels whose quantum numbers are n (as just calculated) and n + 1? Would quantization be measurable in this case?

I'm too old for this!

I would say that the 'bending of the string' on a swing is a minor component of how the extra energy is added to the system. I would recon that the weight (in)balance is a much larger factor. I also feel that stretching out your legs is only done because it feels good to the human - it creates balance in the position you sit in. Not stretching your legs on the down-swing would gather more weight closer to the center and therefor add a bit more speed. But I could be wrong of course...

This felt like an epiphany, I really gotta go out and try a swing some time soon xD

Anyone else notice the Carlsberg beer truck drive by at 5:00 and fancied a pint?

The professor is correct however his wording can confuse. The swinger resets the pendulem to the longer length (length being determined by the position of the pendulem center of gravity) at the ends of the arc when centripetal force is tending towards zero. The swinger engages in work raising the center of gravity (effectively shortening the pendulem) when the centripetal force is at its maximun (near the bottom of the arc). As in a gyroscope, work expressed against the direction of the centripetal force will result in an acceleration at a 90° angle to the centripetal force. The bend in the swing chain indicates the raising of the center of gravity, but the raising of the center of gravity by the work of the swinger will occur whether the swing is suspended by a chain or a bar.

When you throw your feet back/forwards at the highest points, doesn´t that also have an effect? Intertia is probably playing a role here (when throwing your feet back/forward, I think you can gain a few centimeters of height, because your´re investing energy to change your center of mass)

"This video is brought to you by Carlsberg"

i just had a dejavu about this video, it feels like i watched it yesterday but infact i've never seen or heard anything related to swing before. This is the first time i'm watching this video. WTH??? LoLL

Watch at 2:44 and 5:10. He contradicts himself. Of course it works if you shorten the distance at the extremities. If you do work at the extremities by pulling yourself up, this energy gets transferred into kinetic energy.

Hello I would like to ask a question , is it possible to destroy a black hole ?

Swinging in a swing works by moving your own CG of mass forward and backward from the center of the pivot point, else it wouldn't work in the event of rigid bar swings, you are lengthening AND more importantly moving the CG of mass by leaning forward and backward.Sixty symbols typically nail it, but they missed with this one.

Physics is fun!

Isn't is centripetal force not centrifugal force? As the tension is always toward the centre of rotation?

My whole life has been building up to this moment

Yes thank you 🙏 watched video ✅

So why is it when you flip around the motion (leaning forward when going forward and backward when going backward) you slow down? You're still shortening the length of the pendulum which would then accelerate. Anybody?

This reminds me of when ever I go fishing with my friends and my hook goes over a branch. I do that same motion of pulling on the string to get the hook over the branch without having to cut my fishing string.

I think just moving your legs is enough. I never remember pulling on the strings/chains of a swing. As long as it moves your centre of mass up or down it should work, right?

At the start he reminded me of Stevie from Malcolm in the Middle - but overall great video.

I'm not saying he's wrong, but he obviously doesn't have the whole story. I think a bigger piece of the puzzle is simply moving the centre of mass off axis, thereby moving the resting point of the swing. This is pretty clear when you start swinging from a stationary position.

Really want to go to the park now