[DEMONSTRATION] - Coupled Oscillators

so this beating phenomenon that you just just saw and heard here is actually similar to a subject that is concerned with a lot of different types of oscillations it's when you have more than one oscillator and they influence each other they're not just freely oscillating we call those coupled oscillators and here's a very simple system of coupled oscillators here's a pendulum everybody see this you see the notes of a string there the line okay here's another pendulum right and what's the relationship between those two frequencies they're the same as by symmetry this frequency is going to be this friggin so I'm going to start the energy off in this pendulum so this because of the knot that's here they're coupled they influence each other so this motion is going to drive that and because it has the same frequency watch what happens I start the energy off in that one it starts the other one moving and right now there's been complete energy transfer over here and now the roles are reversed now this one's going to drive that one and it just goes back and forth now you can't make this at home it's way too complicated right you can make this at home right and what an advantage of making things is then you start to you start to learn more you start to think what if the frequency of this is not the same as the frequency of that what do you think is gonna happen now we can't demonstrate that we'd have to rebuild it right no okay I just changed the apparatus what did I do this is a shorter pendulum so the frequency is faster it is greater right so now watch what happens when I start the energy off in this one carefully watch this it transferred some of the energy now it's coming back did it transfer all the energy now only in this resonant situation do we get that complete energy transfer now this just looks like one oscillator it's just going to go up and down sorry this just looks like a single oscillator doesn't look like it's really coupled to anything not all that interesting but look what happens when I change the mass watch what happens I start this mode off whoa who did that well this has this can oscillate longitudinally oscillate like this there's also a pendulum over here there's also a twisting moment and somehow there's a there's a resonant situation here this mode is pumping energy and into this mode this is a lot more complicated than these other ones it turns out but it's important because this has actually happened to ships what you just saw there under certain conditions of ship being hit by waves bounces up and down and under certain conditions there has to be a resonant condition it conclude this energy can go into this rocking image and there's one report that it apparently caused a ship to capsize that's an old report people aren't sure about it but there's a recent one in the 1990s where it caused a ship to go back and forth roughly 50 degrees plus or minus and it caused extensive damage all of a sudden after that were always all these conferences one was even here on understanding it and it's all you just saw the effect the basic physics is right here okay now here's another mass on a spring I don't know if everybody can see this I'm gonna my am I going to destroy anything okay everybody see this okay this actually has a name it's named after the inventor Wilberforce a couple hundred years ago early 1800s why does it have why is it named after somebody it's just a mass on a spring right well it's been carefully constructed you can see these adjustments down here such that this frequency is the same as the twisting frequency and they're coupled because have you ever taken a spring and stretched it what does it want to do it wants to unwind when it compresses spring it wants to whine so these are their coupled oscillators here watch what happens I'm going to start the energy off in the longitudinal mode okay just lift it up here let it go and you can see it's now driving the torsional or twisting mode and because it's a resonant situation what's going to happen we should get complete energy transfer and it's happening right about right about there almost complete and now it's gonna go back so this is a very dramatic demonstration that's why we've got a name here it's been popular with students and other people for 200 years but I want to point something out to you it's essentially the same physics as this the one here this one it's just a lot more dramatic because it's converting I think the longitudinal one of the twisting but it's the same idea same idea

Channel: NPS Physics

Views: 16,295

Rating: 4.9679999 out of 5

Keywords: Coupled Oscillators, pendulum, physics, physics demonstration, bruce denardo, Naval Postgraduate School (College/University), coupled oscillator, Oscillation (Literature Subject)

Id: ljaQr6YOVnk

Length: 5min 39sec (339 seconds)

Published: Mon May 04 2015