Types of Waves

by Patrick Ford
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Hey, guys, in this video, we're gonna talk about types of waves. Alright. It turns out that you can divide waves into two broad categories called trans verse waves and longitudinal waves. So we want to know what makes a wave trans verse and what makes a wave longitudinal. So let's get to it. Remember that a wave is a moving oscillation. Okay, It's a moving disturbance in that disturbance is oscillate. Torrey. Okay, that means that a wave has toe have two directions that are important. An oscillation direction. Okay, what way do those oscillations go? Do they go up and down? Do they go forward and backwards? Do they go side to side? And it has to have a motion direction motion we will often refer to as propagation. Okay, so I will use those words interchangeably. Now, as I said, the two broad categories of waves that we can dump everything into our trans verse waves and longitudinal waves. And the difference between the two is the relationship between the oscillation direction and the propagation direction. Okay. And transverse waves. Oscillation is perpendicular to motion or toe oscillation. Okay. For longitudinal waves, the oscillation is parallel to the motion or to the propagation. Trans verse waves are very, very easy to draw. Imagine having a string anchored at a wall and you can hold on to the freedom of the string and you just whip it up and down. You're producing these pulses that are all traveling along the length of the string, so they're traveling horizontally and the vertical position of the string is going up and down, up and down. So there's an oscillation in the vertical position off the string that's along the Y axis. It's vertical, so it's propagating on the X axis horizontally and oscillating along the Y axis vertically. So this is clearly a trans verse wave, the oscillation directions perpendicular to the propagation direction. Now, let's take a very common example of a longitudinal wave. We have a spring anchor to a wall where you could grab the free end of the spring. But instead of whipping it up and down, you push it back and forth. What that's gonna cause is this gonna cause traveling clumps of compression along the spring. So you're gonna get areas where the spring is stacked up really, really, really close to one another. this area of compression, and then you have areas of the spring where it's spaced very, very far apart. It's stretched, okay? And this is technically called rare faction, and you get oscillating compression and rare faction compression and rare faction along the propagation direction. Okay, so this oscillates back and forth along the same direction that the waves are moving. This is why this is a longitudinal wave. Okay, Now both types of waves have to carry energy because all waves carry energy long. I'm sorry. Trans verse waves can carry energy of multiple types. They can carry a whole bunch of different types of energy. And it really depends on the type of wave that it is a wave on a string, which, as I showed above, is it. Trans verse wave carries mainly kinetic energy due to the motion of the string, but it also carries some potential energy because the string actually stretches when you whip it, you have to increase the length to allow for these hills and valleys, so there's some compressed. There's some potential energy due to the stretching of that string. Water waves carry a ton of kinetic energy. Ah, tsunami Can be 100 ft tall. All that water has a lot of mass, and it's moving very, very quickly. Maybe 100 kilometers an hour. Okay, so that carries a ton of kinetic energy Light on its own carries something called electromagnetic energy. But light is not something we're gonna cover here. It's something you're gonna cover much later on in physics. Okay. Now, longitudinal waves mainly carry energy in the form off potential energy due to compression. Okay, The most common type of longitudinal wave is a compression wave in some sort of elastic medium. So if you look at the spring springs air clearly elastic, right, they can stretch their return to the original configuration. They can compress their return to the original configuration. So the energy is carried by the potential energy due to these compressions which are collapsing it into a smaller sorry distance that it should be and rare factions which are stretching it to a larger length than it should be. Both of those give it potential energy. So there's a lot of potential energy in this wave. Sound carries energy on its own two. But sound is actually just a type of compression wave in an elastic medium. Gasses, liquids and solids, which are all media that sound can propagated. All have elastic properties. And, as we'll see later on, sound is just a compression in this a lot. And these elastic media All right, guys. So we have Remember, guys, we're focusing on periodic waves, waves that have repeating cycles and periodic waves. Regardless of whether they're trans verse or longitudinal, obey the same equations. Okay, they have the same characteristics that you could describe. You can talk about amplitude, wave length periods, speed frequency all the same characteristics, and they obey the same speed relationship. Lambda F. Okay, very important to remember that regardless of whether it's a longitudinal wave or a trans verse wave, they obey the same relationship. All right, let's do a quick example. Can longitudinal waves propagate in a fluid? What about trans verse waves? Absolutely. Longitudinal waves can propagate in a fluid because, as you're compressing the fluid, the fluid wants to not be compressed. It wants to return to its original size. Okay, fluids are very, very resistant to compression, so they can propagate compression waves very easily like sound Alright, Now the problem is can they be? Trans verse waves? No trans verse waves do not propagate very, very well in liquids at all. The reason is, is that if you think about the actual molecules inside of the wave, sorry inside of the fluid. When you give it some sort of lift, right, you want those molecules to start going up and start going down right like a wave while it propagates in this direction. But the problem is that centrally to the wave is oscillation. So as this water molecule goes up, it has to come back down. But there's no elasticity. There's nothing to bring it back. Okay, this is different than a wave on a string. When you whip a wave on a string, the wave stretches to allow part of it to go up, and that's stretching stores potential energy that snaps it back down. But there's nothing holding those waterway those water molecules in place, so longitudinal waves propagate very, very well in fluids, right? I chose to talk about the liquid here, but it's saying for a gas, and they propagate very poorly in trans verse waves. Alright, guys, that wraps up our discussion on the types of waves. Thanks for watching. Okay,