Okay, this video is about standing waves and resonance. We've got a very simple setup. This is an old speaker, to which we've attached a bit of a rod, a heavy weight, a piece of elastic string and something to generate a signal. Now if I pop the signal on, you can see that the speaker is going up and down and at the moment I've got it working so that this end is acting like a bit of an anti-node, the note about here, the note on the other end is about there and we've got just half a wavelength. If it's slightly off its resonant frequency, so I'll turn it slightly down, maybe I'll turn it slightly up, then you don't get the wave forming nicely in the middle, it's all a bit messy. If you get onto the next frequency, or another resonant frequency, you just have to get it perfect, so it's very fiddly, but now you can see that we've got one, two, three, four, five, six, seven half wavelengths. So we've found a higher resonant frequency with seven half wavelengths. Resonance is where if you put in a little bit of energy, if you're at the right frequency, the amplitude increases. If you're at the wrong frequency and I'll just turn it off again, the amplitude doesn't give you the right frequency, you don't get the standing waves forming. Standing waves occur when you have a pulse that's sent down the string, reflects off the end and comes back and the wavelength is just at the right length so that half a wavelength, multiples will fit into the length of your string. So this is one way of demonstrating resonance.