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Learn the toughest concepts covered in Physics with step-by-step video tutorials and practice problems by world-class tutors

11. Momentum & Impulse

Types of Collisions


Overview of Collision Types

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Hey guys, so remember that we said that interactions between objects can fall under either collisions or push away problems, but there's actually three types of collisions that you're going to have to be able to identify. So I'm gonna go over sort of a conceptual overview of these types of collisions and we'll talk about them in more detail later on. So let's go ahead and talk and take a look here. The to sort of basic categories are elastic and inelastic and an elastic break down to two different categories. That's why we say that there's three types. So what's common about all collisions is that momentum is going to be conserved in all collisions. We're always gonna be able to use conservation of momentum. If you start out with 10 momentum, you have to keep the same 10 throughout these problems, no matter what type it is, The difference really comes in when you when you start to take a look at the energy. So what really separates these two sort of types is whether energy is conserved or not, an elastic collision is going to conserve energy. So if you calculate 20 jewels of mechanical energy initial, you're gonna end up with 20 jewels of mechanical energy. Final, that's sort of the defining characteristic about them. So what happens is momentum and energy could conserve, but the objects don't stick to each other and we'll talk about that with means in just a second here, an inelastic collision is going to conserve momentum but it's not going to conserve mechanical energy. So you're always gonna lose some mechanical energy here. So the setup is that you have these objects that are sort of crashing towards each other, you're gonna conserve momentum. But when you calculate the mechanical energy, there's always gonna be some loss. Just making up numbers here here you have 20 here, you have 10. So there has been some mechanical energy that's lost their. So this is sort of like a general an elastic collision. So you have momentum conservation, not mechanical energy conservation and the objects don't stick to each other. Basically, these two things are sort of going slower and after the collision. Alright, so an important subtype of these type of an elastic collisions is what's called a completely or perfectly inelastic collision. The setup is a little bit different here, but basically you have one object that's going to hit another one and those things are going to stick together and they're gonna move together as a system. So the defining characteristic here is that objects move at the same velocity after they collide they move together like this. Now this is really just a subtype. It's still in an elastic collision. So you still have some mechanical energy loss. So what happens is you have momentum conservation, you do not have mechanical energy conservation. But what's defining about these is that objects are gonna stick together? All right, so that's sort of like a general review of these types of problems. Now students I always get confused between elastic collision versus a totally an elastic collision versus a general and an elastic collision. So what I always like to do or sort of visualize is a bouncy ball that's sort of going up a sort that's hitting the floor. And we want to take a look at the energy of that bouncy ball. If it's a completely elastic collision, we know that mechanical energy is can be conserved. So if we drop this ball from one m, it's going to fall down to the floor and it's gonna rebound upwards and it's gonna rebound to the same height because there's no energy loss. So the ball returns to the same height. An inelastic collision always loses some mechanical energy. So if the ball falls down to the floor, the ball has to return to a lower height. It could be 0.1 m, it could be 0.5 m, it could be 0.9999 But if you ever have some energy loss, that's always going to be an inelastic collision, no matter how close it is to zero or one or something like that. Right? So completely inelastic collision is going to be something like the ball is going to fall to the floor and it's just gonna get stuck there. These two things are going to have to fuse together um or stick to each other. Right? That's what sort of defining characteristic about them. So, these terms are often kind of confusing, completely elastic or completely an elastic or something like that. So what I would like to do is I kind of like to envision like a like a spectrum of how elastic the problem is. And the best way to tell which type it is is to look first if it's completely in elastic. So if it's completely in Alaska, you're gonna be looking for objects are sticking to each other and if it's not one of those types of problems, if they don't stick to each other, you're gonna go to the other side of the spectrum. You're gonna figure out if the object if the problem is completely elastic. And to do that, you're gonna look at the mechanical energy. If you can calculate the mechanical energy and you figure out that it's conserved, then it's completely elastic. If it's not one of these two problems, if it's not completely an elastic, if it's not completely elastic, then it sort of falls into this sort of partially in elastic. So this is gonna be like partially in elastic here. And whether, you know, it's whether it's like almost elastic or whether it's almost an elastic, it doesn't matter because it's still just gonna fall under sort of this general sort of partially in elastic category here. So this is gonna happen every time you have some mechanical energy loss. Alright, so hopefully that makes sense, guys, let me know if you have any questions.