 Let's talk about oscillators for a moment. Now an oscillator is just something that can oscillate and lots of things can oscillate in fact nearly everything we meet can oscillate if organized quickly here are just three things I've found that people had left around my room and if I tap them You can hear that they make quite clear distinct sounds and that clear single frequency that they're giving off is Low in that case and high in that case and it's wearing off after a while And the fact that's wearing off means it's losing energy to its environment and that's called damping and so this thing here Gives off some sound and then it's lost its oscillation and so it's damped if I had the desk The desk is highly damped and it has a very broad spectrum of frequency So that didn't sound like it had a very clear frequency at all But it had a very broad spectrum and it was very strongly damped Alternatively you might have something like a tuning fork a tuning fork is very specifically designed to have low damping so that it keeps its note for a long time So it has a beautifully clear frequency We're just designed to have and it also has very little damping to its environment and so you can use that to Check the notes of other things and you also have other kinds of oscillations like a pendulum Which can oscillate for a while and it'll eventually get damped as well in this case largely because it's losing energy Because I'm not holding it too well with my arm and so it's losing energy to my arm Now it's no accident that the things that we saw were very highly damped Tended to have less clear frequency. So the clearer better frequency you could hear the less damped it was That's easy to understand if you look at the wave for a very clear frequency Remember as we go along in time a very clear frequency looks like a sine wave and If you have something that's really highly damped Then it doesn't look like a sine wave And certainly not obvious But you can make any kind of waveform out of a bunch of sine waves We need lots of different frequency sine waves in order to make something looks damped compared to something looks exactly like a single frequency like a single sine wave So for some purposes you definitely want to build something with very low damping So they get a lovely long pure sound and this tuning fork because it's got low damping Let's us have a nice frequency with which we can set other frequencies But sometimes you want to build something very deliberately with high damping And that's because the coupling of energy between an oscillator and the environment can go both ways for example take a swing So if you've got a swing if you push this at one frequency That's not the correct frequency for the swing. So it's natural oscillation frequency Might be particularly slower than this and it doesn't matter if I push it really quite hard If I'm pushing at the wrong frequency, but if I look okay, that's the frequency it has naturally and if I tap it With that frequency I get very big oscillations very fast So I couple energy from my environment to an oscillator much much better as at the particular Natural frequency of that oscillator and that phenomenon is called resonance and that frequency is the resonant frequency