Wave Properties
Physics
Okay, this is the next video in our wave unit and it is about wave properties or how mister bread the bread. Belle shreds on jingle bells. If you don't understand the reference, it's because you weren't here during Christmas and you're not in a learning community. But whatever. So the objectives of this unit is that by the end you are responsible for being able to do all of these things, which means if there's a quiz, you should be able to do all these things on that quiz. And that would be defined and apply the terms longitudinal transverse mechanical pulse periodic compression, rarefaction, amplitude, wavelength, crest, and trough. I know there's a lot of words. And then calculate the velocity of a wave, and then understand the main source of wave energy. So question what do the ocean, the sound of a whale, and a lighthouse having common? In the answer is, they are all example of waves. In a wave is anything that causes a disturbance and is tied to emotion. So a wave is just the motion of a disturbance.
So for example, if you are looking out on a Lake and you see little water droplets are like a pond and something splashes in the pond, that's a disturbance. And that creates a motion of disturbance that ripples throughout the Lake and that's what a wave is. So anything that causes a disturbance is can be a type of wave or anything that causes something that fluctuates is considered a wave. And so there are many, many types of waves, and we're going to talk about really like three different kind of classifications and each of these classifications have two types. So the first and really all of these kind of have questions. So the first kind of classification is medium. And so does the wave require a medium to travel through. And so like water would be an example of a medium or air would be an example of a medium, just something for it to actually physically travel through. If the answer is yes, then we call that a mechanical wave. So for example, this guy doing his little fancy exercises using these ropes by making waves in the ropes, it requires the rope, so it's a mechanical wave. If it doesn't require matter as a medium, then it's electromagnetic because light is electromagnetic, and it doesn't require matter. It can go straight through empty space or a vacuum. It doesn't have to have air present like sound and other mechanical waves do.
The second classification would be how does this disturbance occur? Because remember a wave is just a disturbance. So if the disturbance or motion is parallel to the direction of the movement of the wave, then we call that longitudinal because think of like the word longitude is like a parallel line that wraps around the earth. So if it's parallel to your motion, we call that a longitudinal wave. And so an example would be sound and slinkies. Think of like a slinky if you like little compressions through it, they will travel along the direction of the slinky that's parallel to its motion, like it's moving this way and it is vibrating like this as it goes down the slinky, okay? The other option is that it's perpendicular to motion and all simple harmonic motion falls under this category. And that would be called transverse. And so it's because it's moving up and down while it's moving sideways. So that's perpendicular to its motion. So it moves in you end up getting sine waves with transverse. And so an examples would be ropes, water waves, like if you go to the beach, light is a transverse wave, and yeah, sine waves. Anything that's going to make this pattern is considered transverse.
So the third type or third category is so so far we have mechanical and electromagnetic longitudinal transverse. And so our third category is how long does this disturbance occur? And really what is going on? If the disturbance only occurs once, like you threw a rock in a pond. That's called a pulse wave. Where you just have one little single pulse travel through. So this guy creates a small pulse in a rope attached to a wall. And so it's not occurring over and over. It just occurs once. The other option is that it is regularly or periodically occurring. And so we call it a periodic wave. So like in class, if something is happening over and over and over, think of a lot of pulses, many pulses create a periodic wave pattern. And again, it looks like a side. Okay? So now we're going to need to fill in some vocab into these kinds of waves. And we're going to use this vocab for the next two units. So it's really important that you understand what each of these terms means. So first of all, this is called a trough.
A trough is either for like putting plants in or often used for feeding animals, but it's like a bowl, like a long bowl that you put food in, okay? This is called a hillcrest. Notice like the top of a hill is called the crest of a hill. And so this little cow is grazing on the crest of a hill. So when people first started talking about waves, they called the top of a hill, the crest, and they called the bottom of a hill, a trough, because this looks like a bowl, and this looks like a hill. So the crest and the trough, and then the distance between two crests or really two places on any two places on the same wave. So like here and here, or the crested crest, trough to another trough is called the wavelength. And it's literally just the length of the wave. And we use this little funky letter if you play half life, then you recognize this, but it's called a lambda, kind of like a little lamb, grazes on top of the crisp. Of a hill, it's called a lambda. Okay? And then our last word is that if this is our equilibrium line, where it's going up and down, kind of like the spring, then these two heights would be considered amplitude. So the distance from equilibrium to the highest or the lowest point is the amplitude of a wave.
For longitudinal waves, we have a kind of different terminology. So first of all, this is a animated file showing you kind of what a longitudinal wave looks like. Maybe like over a plane instead of just in a slinky. But notice that you have these lines compressing and it travels through this compression, travels through in perpendicular to the direction that it's actually moving. Sorry, parallel. Longitudinal is parallel. But it's not like waving up and down, like a sine wave. It's just kind of like compressing and moving in the same direction. And so this is often with sound. And so sound basically causes these areas of really compressed air. And this kind of like waves and travels from the speaker to your ear. And next unit that we do is sound. And so we will talk about this in much greater detail in a second. But if this is your slinky longitudinal wave, then the wavelength is, again, from a one compression to another, and so basically, instead of having crests and troughs, now you have compressions, which are areas of high concentration, and then you have rare factions, which are areas of very low concentration. And the way I always remember this is because during a rare faction, it is very rare.
You don't see very many slinky coils together because they're rare. And so rare faction is when it's not very clumped, compression is when it's really clumped in a wavelength is from one compression to another, or one rarefaction to another rare faction. And longitudinal waves are almost always caused by compression. And then amplitude is the amount of compression. How squish it is. So instead of like height being amplitude, amplitude for a longitudinal wave is how dense is this compression right here. Okay. And so for a wave, is really easy to find velocity, because if you think about it, velocity is distance over time. And so the distance that a wave travels is technically wavelength, and the time it takes to travel would be one period of a wave. So you have lambda divided by capital T, think of period, okay? And so if frequency is one over period and I have a one over period here, then the velocity of a wave is the wavelength times the frequency. And velocity is in meters per second, wavelength is a meters, frequency is in hertz, but remember it also is like one over seconds. So meters times one over his meters per second.
That all works and matches. And lastly, for the energy of a wave, waves, primarily transfer energy. If you think about it, like the sun is an example of light waves and they carry a lot of energy. And if you don't believe me, the other waves don't carry energy, just go to mission beach in San Diego and spend an afternoon getting pummeled into the sand by these ten foot waves and you will definitely remember that waves have a lot of energy. Or you can just think of all the tsunamis that displaced millions of people from their homes. So waves do carry an incredibly high amount of energy. And this wave energy is based on amplitude. If you think about a tsunami versus a small beach wave, the difference is that a tsunami has a huge amplitude, a huge height to its wave and that carries a lot of energy. In fact, the energy is proportional.
That's what this little guy means, this weird half infinity. Energy is proportional to the square of the amplitude. So if you double the amplitude, the energy goes up by four, like four times greater. So that's why tsunamis are so devastating because they carry a lot of energy. Okay? And then if you think of a guitar amplifier, the word amplifier comes from the fact that you are increasing amplitude, which obviously is going to give you more energy. So the answer to the question, how can mister bell shred on his guitar and play jingle bells for fundraisers is because that he can increase the amplitude of his soundwaves using an amplifier. So there you go. And that is the end of this video, and we will talk about this more in class.