How Swings Work - Sixty Symbols
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- Опубликовано: 28 сен 2024
- Swings, pendulums, parametric resonance and all that.
More at: • Swing Physics (extra f...
And slow motion at: • Swing Slow Motion
Featuring Professor Roger Bowley.
Want to dig even deeper - Professor Bowley recommends reading Classical Mechanics by Leonard Susskind and George Hrabovsky - bit.ly/classica...
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This project features scientists from The University of Nottingham
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Sixty Symbols videos by Brady Haran
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"there, there, there, there.....oh dear, it's getting a bit too violent for me."
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.
Exactly. I'd argue that the effects shortening of pendulum length are insignificant compared to energy from moving your centre of mass by moving your legs and torso up and down. Best exemplified in standing rigid swings where all of energy comes from squatting down and standing up at the right time.
seems like got some centrifugal force during the lean back.. maybe this will add extra force...
For those of you asking about swings with rigid bars rather than flexible chains, see the "extra footage" here: ruclips.net/video/eY-SWHMCakY/видео.html
Well, I remember that I used the same technique on a swing with rigid bars as here in the one with chains(without standing up like in the extra footage). Can you explain what's the deal there?
I just wanted to ask the same thing!
I think when you stretch your legs you are also leaning back, and that lowers your center of mass because your belly button is level with the swing. But I am still not sure when you are stretched out (longer pendulum) and when you are sitting straight (shorter pendulum) to make it work. Also, again, maybe it has to do with something other than long/short pendulum, for example, maybe you are moving your center of mass back or forward in comparison to the swing seat.
Having worked as a professional tree Man , the times when I would have to take down large trees , with little to no margin for error , I would set my pull line at different strategic points , depending on the lean , angles , direction of the wind , in addition to taking into consideration all the branches and their weight . If I could do a large tree without climbing , these calculations saved me a lot of difficult and dangerous work , besides time . I've always wondered what types of math I was instinctively using to figure all of these factors out so quickly .
Thanks !!!
Keren Duchan
I agree, I'd say that added perpendicular distance causes a torque that amplifies the swing height.
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.
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.
What about swings with rigid supports instead of chains?
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.
I must agree with this man's analysis. Rigid bar swings do work and i do believe shifting your center of mass (slightly higher) is the cause of the incremental increase in energy each time as you can only raise your center of mass (relative to the seat) abit at a time.
He's a physicist and your not. I think he knows what your talking about. A
i guess the english people havent seen ones like ours, пред блока :D
he said it from the start. The distance is not the rope it self, its the distance from the pivot to the center of the mass that is swinging. Meaning if you have twisted metal pipes going left and right it still doesnt matter if you can change the position of the weights (meaning you).
@@deliciousbutter6077 replying to a 7-year-old post with "ur mom"
Glad to see Professor Bowley again, I was worried we wouldn't get any more videos with him since he retired.
I'm so glad to see Professor Bowley is still making videos!
***** Oh boy, I'm not. Can't stand the guy and think he's the very worst of all the professors. In fact, I find every single other one of them excellent except for him.
When he announced he was retiring I thought "Thank fuck for that", but the old bastard won't piss off.
I smiled way too much when he was playing with the swings.
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 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).
4:53 The most subtle product placement ever.
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.
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)
I thought similarly. as the speed of "rotation" is fastest with the swing or pendulum perpendicular to the horizon, and that's the point where you'd move the center of mass toward the pivot point, that should increase the speed.
the next thing I wonder about is how the effect is amplified rather than cancelled out? if an ice skater starts spinning with their arms and legs out and the spinning increases speed when they bring them in, the speed decreases again if they spread their arms and legs back out.
of course energy is added to the pendulum/swing system by an external force moving the center of mass toward and away from the pivot point, but what describes how that energy magnifies the amplitude of the swing?
perhaps moving the center of mass away from the pivot point at the far extremes of the swing doesn't act subtractively like it would for the ice skater because the system is temporarily "at rest". and/or perhaps that movement at that point increases the potential energy for the center of mass.
That's awesome. You got to love learning the science of seemingly mundane everyday things.
first. :)
I thought Professor Bowley retired. So happy to see him again! :D
The lifting and resting of ones legs also lends itself to the shifting of one's center of gravity upward and downward.
Props to the Professor (?) for laboring for science!
I always thought it was the leg swinging which made you go faster. This has been enlightening!
I thought he had retired? It's nice to see him again, a great teacher.
THOSE SLOW MOTION SHOTS WERE SICK
I bet people driving by were wondering "Why is that man videoing an old guy trying to swing??"
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.
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.
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?
I've often wondered how swings operate. This is amazing!!!
Finally an answer to the question I was asking myself again and again. There was no good explanation on youtube so far.
Roger always gets to do the more physical/strenuous experiments. hilarious and impressive at the same time. cheers to the Emeritus! :)
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.
Anyone else notice the Carlsberg beer truck drive by at 5:00 and fancied a pint?
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.
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?
Fantastic video
Very interesting, as always! Keep up the good job, can't wait for the next video!
this solves my question that i had for swing sine i was a child... thank you...
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 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.
Great explanation. Thanks prof bowley
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?
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.
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)
Does your university have a swinging class?
Every fourth full moon that falls on a Thursday of year unless their are 49 or more parking spaces open at the primark within 60 miles.
Oh. So that's somewhat regularly then. Must be a swinging success.
Why should centrifugal force be present in order to do work on the system. The tension in the string exists even without motion due to the weight of the mass attached. So, why should you need to apply force only when the mass is at its maximum velocity? Something to think about...
A great video. Thank you
This video is hysterical! :D
"Oh dear, it's getting a bit too violent for me." XD :3
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.
Note that reseting pendulum length at the ends of the swing arc when centripetal force is near zero results in little to no change in the speed of the swinger, and is accomplished by the swinger with little to no effort (work).
My whole life has been building up to this moment
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
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!
Could we please have a video of just Mr Professor on the swing in slow-motion? ;D set to some heavy metal
5:00 That calls for a Carlsberg! Cheers :)
Can anyone explain to me how the shortening of the string equates to putting energy into the system?
Centrifugal force? Centripetal maybe?
But then surely by that explanation it wouldn't matter if you pulled on the chains and lent back when going backwards on the swing as it is still shortening of the rope? But that slows you down, why?
The shape of your triangle would extend the effective length of the pendulum so you have the opposite effect. You need to lean forward to move your centre of mass closer to the pivot.
Ah yes thank you
By shifting the position of the rope while you're at one end of the swing, you keep the rope at a higher angle longer, imparting a larger horizontal (useful) impulse onto yourself. When ever you go from leaning back to leaning forwards, your essentially continuing to naturally fall while you keep your hands up and in front of the swing where they can try to pull the swing set forwards, accelerating you back for and extended amount of time. Remember that the only forces acting on you are along the rope (tension) and vertical (gravity).
Really, it's easier to understand if you just imagine yourself having giant, really long arms, if you were holding onto a rope and swinging and you were at one end and wanted to get to the other end, you'd use your long arms to hold the rope out at a diagonal and pull really hard in order to force yourself to the other side.
because when you shorten it on that side you are adding the energy in the opposite direction to what the swing is now going- so fighting it and reducing the speed?
Still don't understand. How does the change of length actually cause motion?
What they sort of Glanced over was what kind of energy is in the pendulum/swing system. You have potentional gravitational which depends on your high of the ground (changing the length of the string to be shorter makes the mass higher so it has more energy) and at the bottom is has full kinetic energy resulting from converting the entire amount of potential energy (which is maximum at the tops). So by reducing the length of the wire, you give the system more energy to use, making it go faster at the bottom and higher at the edges. (potential energy due to gravity = Mass*g*height . Kinetic energy = 0.5*mass*Velocity squared). Hope this helps!
Froggeh92 So your basically adding potential energy that is then converted to kinetic energy?
Exactly. Or thats what i understand.
Think of it like this. You know the energy in the system needs to stay constant, right? So if you decrease the lenght the potential energy decreases because (Ep=mgh). So that means the kinetic energy needs to increase as you swing, the increase in velocity allows you to reach further in a shorter period of time.
Froggeh92 thanks guys, that really helps.
I'm too old for this!
This is awesome
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
Centrifugal force i fell is more like a force vector away from the center of the circle. Center-scaping force.
Brady, why only 240p? You're shooting with a C100, surely there must be something wrong with the upload file..
but you could do that even on a swing that is not hung on chains but on non-flexible pipes, i dont think this shortening effect does much there
This was great, thank you!
I stand on it the swing and lower myself/bend my knees near the extremes. It is more effective, but also more dangerous. Now I know why
At the start he reminded me of Stevie from Malcolm in the Middle - but overall great video.
It's cool to learn how they work, those things always make me dizzy though hehe :-)
Physics is fun!
Is it centripetal force or centrifugal force?
I knew the comments on this vid would be a riot, youtube you do not dissapoint
What about swings that aren't held on chain, but on two metal poles? Swinging on them surely works, but you obviously can't shorten the length of the pendulum by pulling on the pole.
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.
This is important science, this.
I'm just waiting for the music remix of 1.26 - 1.46. I know the internet won't disappoint ;)
That beginning bit made me laugh waaay too hard
Circque du soleil uses this all the time and its incredible what heights they can reach
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.
"This video is brought to you by Carlsberg"
There's no science like field science!
Fascinating!! :D
This is a beautiful manifestation of the triangle inequality. (:
How do we know how to do this?
Agreed that the physics work as described but only to a small degree as I can still swing with ridgid poles instead of chains
So it is completely impossible to swing without holding on to the chains with your hands :o I never knew that that was the thing that sets everything in motion.
I was going to ask about rigid bars and then I saw the extra footage lol =P
5:00 Carlsberg don't do lectures on the motion of swings, but if they did ...
You're never too old to be a swinger.
So centrifugal force does exist?
Your University should give your physics department a grant for a larger swing set for ummm... research..yes...research :D
I still want to try swing in swing made of solid "chains".
Yes thank you 🙏 watched video ✅
How does that explain rigid swings, where no chain is used, but rigid bars instead.
If you were to repeat the first experiment in a zero gravity environment, the pendulum would go around in a circle. What would be the effect of shortening the string?
You would accelerate.
Since you don't have a lowest point any longer, nothing.
5:03
Shameless Carlsberg product placement!
am I wrong for challenging the professor, but there is no such thing as centrifugal force, isn't it actually centripetal force? where the extremities are actually accelerating toward the centre of rotation?
or am I just not very good at physics? hahaha! probably the latter
Ok thank you got it
Why am I able to feed energy without any external force? Anybody?
Best video starting ever!!! Jajajajajajaja
That calls for a Carlsberg