 Hi, sorry, I was just making some sound waves here with my guitar. You probably know me as Mr. Lyingdell, but I'm also lead singer and guitarist for the hit band Teacher Band. Teacher Band, of course, being the most amazing band you've ever heard of, made up entirely of teachers playing classic rock from the 80s. Sound is a great example of a wave, and we can start looking at some of the definitions and parts of a wave by taking a look at some sound waves. All right, let's take a look at a sweet sound wave coming out of my guitar amp, so we can learn about some of the different parts of a wave. First of all, you can see the wave is kind of broken into these crests and troughs. The crests are the part of the wave that are above the equilibrium line. And equilibrium is just like we had back when you're dealing with mass spring systems, where the wave would sort of start off. Troughs are the area that are below that equilibrium line. And if you're to take a ruler and measure the displacement from equilibrium, either up to a crest or down to a trough, that distance would be called amplitude. That's also a carryover from the simple harmonic motion section of the unit. In order to get one full wave, you need to have a crest and a trough, a full crest and trough together. And that could look like this, or that could look like this. Either of those are one full wave. If you're to take your ruler and measure horizontally the length of one wave, a full crest and trough, which you'd get is wavelength. Wavelength goes by the Greek symbol lambda. It's kind of that funny looking squiggly symbol there. If you took out your stopwatch and you timed how long and seconds it took to make a single wave, one crest and trough, that time would be called the period. And if you counted how many full waves fit into one second of time, that measurement is called frequency. Period and frequency were also in the first part of the unit, and they were related by the formula frequency equals one over period, or period equals one over frequency. All right, it's dusk. I'm at the park. We're going to see if we can catch a few waves out in the wild. I hear they're nocturnal. See if we can get some video. We've all seen the familiar ripple pattern when you throw a pebble into a pond, but if you stop and look really carefully, you can see the crests and troughs, especially when you first look at where the pebble hits the water. You can see the areas of the water that are above and below the surface of the water. As the waves spread outwards from the point source, you start to see repeating patterns of troughs and crests. If you stop the pattern and measure the distance between any two consecutive crests or any two consecutive troughs, then you get wavelength. If you start it going again and you count just how many crests and troughs together pass every second, then you've got frequency. We've looked at sound waves. We've looked at water waves. Now we're going to go take a look at some waves on a spring. On this spring, we can see the coils move up and down as the wave goes. But on this spring, the coils move side to side as the wave moves down the spring. This means there's two categories of waves, the transverse wave, where the particle movement is perpendicular to the direction of propagation. And propagation is just a fancy word for wave movement. And a longitudinal wave. In a longitudinal wave, the particle movement is parallel or in the same direction as the direction of the wave, the direction of propagation. Here's an animation of a transverse wave. You can see the wave looks like it's sort of moving horizontally, but if you take a look at the particles, they're vibrating vertically. So this is a situation where the particle movement and the direction of wave propagation is perpendicular. In this longitudinal wave, the wave still looks like it's moving horizontally, but the particles are also moving horizontally. This is what makes a longitudinal wave when the particle movement and the direction of propagation are parallel. Longitudinal waves don't have crests and troughs. They have areas where the particles are closer together, called compressions, and areas where they're further apart, more spread out, called rarefactions. Oh, and in case you're wondering why we're talking about waves when we're doing a unit on simple harmonic motion, take a look at that particle in the spring. It's acting just like a mass on a spring would. Waves are examples of simple harmonic motion. You can also see transverse waves on a string, like these guitar strings. I hope you've enjoyed this intro to waves. For more information, check out my website, lbindustries.ca.