In the first week, we will talk about the relation between vibration and waves. As you can see using this demonstration, when I oxalate this with this frequency you will see the vibration of a string with a larger or long wave. But if I oxalate this with a different frequency, you will see the vibration with a different wavelength. That means the vibration and waves are very much related. And also if I oxalate this with this frequency, the force I am feeling over here with respect to velocity over here would be very much depend on the frequency and wavelength as we can see over there. The reason why we are using this kind of rather simple example in the force story is because this is mathematically simple and easy to convey the fundamental concept that is related with the vibration and waves. Which is one of them would be impedance. Developing the fundamental understanding using this rather mathematically simple and conceptually simple example, we will go to the acoustic wave propagation problem, as you can see in this rather simple example. This pipe, of course, when I generate acoustic wave over here, the wave will propagate, and then coming back because of discontinuity over here. And this physical phenomena would be very analogous with what you saw on the string. So based on the understanding of the string, you can understand the way preparation in this simple one dimensional acoustic wave preparation. Those things will be what you learned in this first week. Thank you.