What If Swings Had Springs Instead Of Ropes: Autoparametric Resonance

You can also discuss this video on Reddit: stvmld.com/gm9_zcuh The sponsor is Wren: Offset your carbon footprint with Wren and we'll plant 10 extra trees for the first 100 people: wren.co/start/stevemould

I design ships and they can actually experience a form of parametric resonance called parametric roll. The ship’s stability is a function of its waterplane area. Waves can affect this, by changing how much of the ship is in the water at the ends. You can think of this as a torsional spring, with a variable spring constant. If the wave encounter frequency is at or near the ship’s roll frequency, the ship will begin to roll very violently, even in relatively small seas. This effect often causes container ships to lose containers over the side. They deal with this by slowing the ship down, which changes the frequency the ship encounters the waves at.

This is actually how continuous Foucault pendulum demonstrations are typically powered in museums, since you need to keep inputting power to keep the oscillation going without pulling the bob in any particular direction or influencing the rotation of its plane of oscillation.

"The size of spring was starting to get into dangerous territory, like garage door spring" As a garage door tech I appreciate that comment. Working on your own door is statically as dangerous as working on your roof. I've known plenty of other techs and home owner with ER trips and a few that passed from being careless.

As a fisherman I know this phenomena all to well (parametric resonance). Any time I throw my bait over a branch or something I use this method to swing it free.

"You're just shoving the thing, repeatedly." -Steve Mould, describing the gentle act of pushing a child on a swing, 2022

Eh, here I thought we are going to have a new Mould Effect, but instead it already has a boring name as Autoparametric Resonance

Steve's dedication is just amazing! He's spent years to raise his latest physics teaching prop.

6:38 I discovered this as a child and was able to get to get as high as the bar of any swing with almost no effort in as little time as possible. Imagine the heart attacks my parents got each time they'd arrive at the park and see their 10yo (with Moderate Haemophilia) standing on a 3m-high swing going higher than the bar. The issue with your form from what I can tell is that your legs are still bent while you're travelling upward, so you're unintentionally pumping into the swing. Whenever I stand on a swing, I'll only slightly bend my legs and make sure my legs are fully straightened at the same moment I reached the bottom of the arc. I'm not sure if this is accurate scientifically (but it makes sense theoretically) but I found that it was the easiest way to go super high super quickly

"If swings had springs" sounds like a relative of "if wishes were fishes"

Swings on springs would indeed be autoparamedic.

It’s amazing how many things get discovered by pure chance from the exact right combination of things. Like cutting a grape in half (but leaving it connected by a little bit of skin)and microwaving it, turns out it refracts st exactly the length of the wave of a microwave and starts to glow white hot.

I used to have this bungie rope swing when I was little. I always used to wonder why It would bounce around all weird when I tried to swing normally. I guess this is why!

This video reminds me that, back in school, we were asked to do an experiment to fin out what parameters affect the period of the pendulum. I made the (what seemed reasonable at the time) hypothesis that the mass would affect it. So I set up my experiment, did lots of testing and, of course, had a negative result. Undeterred I kept testing, being very thorough. I then got told off, maybe I should try something else. I didn't get good marks for that experiment. Which I maintain is very unfair. The point of science is not have the answers before you test, but to hypothesis and then try to prove or disprove! My hypothesis may have been wrong, but my approach was, I believe, entirely correct. Everyone else in the class tested length. Statistically speaking I think the majority of them must have had prior knowledge of the answer before starting.

A toy infinite pendulum that constantly makes a really small timed pull to keep the pendulum seemly going forever seems like a good idea Would be really cool to have one in a desk

I'm glad Steve mentioned the double pendulum that is loosely coupled. I run into a similar thing carrying my water bottle (it has a string tied to the top, making it a mass at a short distance) and lunch kit (a larger mass at a longer length). I wind up swinging my arm slightly, causing both the water bottle and lunch kit to oscillate rhythmically like a loosely coupled pendulum. Turns out the masses and lengths are such that my water bottle moves counter to my lunch kit and I can feel the resonance build up if I don't slow my arm down.

I freaking love this channel! Steve you are such a talented and goofy guy, as an artist and audio engineer I really love these especially!

Whenever someone brings up resonance, I immediately think of orbits, and as soon as you said you have to put energy in when it is moving the fastest I thought "just like it being more efficient to burn at periapsis to expand/lower the orbit than any other point". Anyway, amazing video, and now I want to find other more unusual examples of autoparametric resonance :)

I don't know why but watching the pendulum gain amplitude from the resonant tugging is very satisfying

I have a toy kinetic double pendulum on my desk. Its powered by AAA batteries to continue motion, but the changes of phase reminded me of the spring pendulum. I love how you use other examples to get a different perspective!