 Hi, I'm Zor. Welcome to Unisor Education. We continue talking about units of measurements adapted for C, System International, and today we will talk about units used in describing waves. It's very simple concepts. You basically know everything when I was talking about all the properties of waves and that was really a complicated kind of part of the course. Now, this is simple because there are only a few and very, again, very simple measures of the waves. I will be talking only about transverse waves and only about uniform waves, which means they are exactly the same in space and in time. Now, this lecture is part of the course called Physics 14 presented on Unisor.com. As usual, I suggest you to watch this lecture and all other lectures of the course from the website because all the lectures are organized in some kind of a logical sequence, there is a manual, sub-manual, etc. There are exercises, there are problems solved, there are exams and there are certain functionalities of the website, which would help, let's say, supervisors or parents, if they want to supervise students, they can actually do it. So, there is a special functionality. Not necessarily you should use it, obviously, you can just go by yourself through the course without any problems. The site is completely free, there are no advertisements, even signing, not really mandatory, unless, again, you are involved in some kind of functionality related to supervisory studying. Okay, so what kind of units of measurements are used in waves? Okay, very simple. First of all, we are talking about frequency. Now, what is frequency? If you have the wave, so it goes like this, and one particular part of this wave, which basically you can have from peak to peak or from trough to trough, which is actually repeatable. So, this is just one oscillation, basically, from top down and then to top, or from down to top and down again. So, this is one oscillation. So, the frequency is basically how many oscillations this particular wave has per unit of time. Well, number of oscillation is just a number, which means it doesn't have any kind of unit of measurement, it's a number, and the time has the unit of measurement second. So, how many oscillations per second? Well, it can be one oscillation, 10 oscillations, 2500 oscillations, or it can be half of oscillation. So, basically, some number and the unit of measurements is one over second. So, if you have 10 of this, it means 10 oscillations per second. If you have 0.57, it means 0.57 oscillations per second. Per second, that's why second is in denominator. Now, this unit is called Hertz. Obviously, in honor of the scientist by the name Hertz. So, basically, the new units, which I would like basically to introduce right now, and it's not new because I was talking about this before. This is just a recap of all units. So, it's Hertz. Hertz is one over second. Well, that's it. Nothing to talk about. Now, the second unit, which characterizes the wave, is period. And the period, again, what I have to realize in the same picture, period is the time it takes for the wave to go from one peak to another. So, obviously, since it's time, it's measured in seconds. And if it's one second, it means the time from peak to peak when, let's say, it's a wave, it goes up and down, or it's an oscillation of a pendulum. It goes from left to right and back to left. That's one oscillation. So, how much time it takes? That's number of seconds. So, basically, it's not a new unit. It's the same second as a unit, but it just measures certain characteristic of wave, which I wanted to talk in. And it's called period. Now, obviously, if you have a frequency, let's say, using lowercase f, sometimes it's used Greek, new. And period, which is usually capital T, they are related. So, if the time from peak to peak is, let's say, T, then what's the frequency? Well, frequency is, obviously, 1 over T. Now, if it's one second divided by how many oscillations are per second, that gives you, obviously, time. So, they are reversed in each other. Okay, so that's the period. No new unit. It's just the same second. What else? In the gate, I'm wiping something, which I should not, again, the same wave. Now, what's the space distance between these two? Because you see if it's, for example, if it's water waves, let's say, an ocean, and there is basically a wave, and then these waves are at certain distance from each other. So, the distance from peak to peak, that's basically a wavelength, wavelength. Sometimes it's written as one word. Sometimes it's like two words. I prefer two. Now, wavelengths, since it's a length, there are meters actually in C, which are used for the length and for distance. So, basically, again, it's not a new unit of measurements. It's the same meter, but used to measure certain characteristics of a wave. So, it's a distance between peak and peak or between trough and trough. And the last one is wave speed. Wave speed is, now, as you saw on the surface of the water, when the waves are coming, the peak goes, basically, from one spot to another. So, there is certain speed at which the peak is moving. So, that's actually measured, again, in something which you know, meters per second. There is no other special units with this. But, anyway, it's, again, it's something which is used specifically for waves. That's the speed with which the peak or trough or any other particular point on the wave is moving in space. So, we have space-related measures, like wavelengths and speed, and we have time-related measures, like period and frequency. Well, basically, that's it about waves. Not too many different new units, just hurts. But, basically, again, the complexity of the waves is not in the measures, how we measure this thing. It's in all these relationship and equations which were introduced in the corresponding letters of the main part of the course. This, I consider, not to be the main part. It's just kind of a recap, only four units, just for reference kind of things. Well, that's it for this particular lecture. Thank you very much and good luck.