welcome to Unit three, where we will be discussing forces and Newton's laws in particular. Now, if you've ever taken a physics class before, you probably remember the word forces. Forces are what we use to talk about accelerations or their rather what causes accelerations. So in the previous sections in the previous units, we've been talking about one dimensional and two dimensional Kinnah Matics, where we had variables like position and velocity and acceleration also are independent variable time. But we didn't talk about what causes thes motions to occur, except for a little bit when we talked about free fall and projectile motion and how gravity was causing an acceleration. Well, the truth is, what gravity is is it is a force, it is, is something that causes an acceleration. Now, not every force will cause an acceleration as we'll find out. But principally speaking, when we talk about accelerations, they're all caused by forces. Now there's many different types of forces. If we think about a box sitting on the floor, we may try to push it with a force, or if we were to attach a rope to it, we might pull it with a force we might sit on it and apply a force. It experiences a force from the ground pushing it up. It may expect experience, a frictional force resisting the direction that it's sliding. There's many different types of forces that we can think about, and all of them can be modeled with fairly simple mathematics. At least the forces that we're going to consider here will be modeled by simple mathematics. There are more complicated forces, but for the ones that we consider working on a box in a macroscopic system like this, they're fairly simple forces. Now we will continue to largely ignore air resistance, which is something that we have done so far with our Kinnah Matics. Simply because, as I said, we didn't have the tools to deal with it. Well, it turns out that we do have some tools that can begin to work with air resistance, but their tools that are insufficient to answer very many questions because air resistance is generally governed by a differential equation, which is mathematics that many of you may not have taken yet. Um, and as such, I will. I will show you a resistance, and we'll talk about extreme scenarios and what it can tell us and how it might affect motion. But we will not do a lot of technical solving using a resistance, and this is very common for introductory physics courses. None of them really cover air resistance in depth, Um, also will use simple models for things like friction that are generally true most of the time, but under specific situations may not be true. So remember that what we're doing here is we're applying simple mathematical models. But the thing you really want to look at is how we do the analysis. Because even if you decide to go farther on and and look at more complex physics courses, the techniques we use for analyzing these systems will be applicable than to, um so we're going to spend the next few videos talking about Newton's laws and what they are and what they mean and how they influence what we're going to talk about. And then we'll move on to our next unit, which will be all about dynamics, that is, to think about systems that are moving in response to forces

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## Video Transcript

welcome to Unit three, where we will be discussing forces and Newton's laws in particular. Now, if you've ever taken a physics class before, you probably remember the word forces. Forces are what we use to talk about accelerations or their rather what causes accelerations. So in the previous sections in the previous units, we've been talking about one dimensional and two dimensional Kinnah Matics, where we had variables like position and velocity and acceleration also are independent variable time. But we didn't talk about what causes thes motions to occur, except for a little bit when we talked about free fall and projectile motion and how gravity was causing an acceleration. Well, the truth is, what gravity is is it is a force, it is, is something that causes an acceleration. Now, not every force will cause an acceleration as we'll find out. But principally speaking, when we talk about accelerations, they're all caused by forces. Now there's many different types of forces. If we think about a box sitting on the floor, we may try to push it with a force, or if we were to attach a rope to it, we might pull it with a force we might sit on it and apply a force. It experiences a force from the ground pushing it up. It may expect experience, a frictional force resisting the direction that it's sliding. There's many different types of forces that we can think about, and all of them can be modeled with fairly simple mathematics. At least the forces that we're going to consider here will be modeled by simple mathematics. There are more complicated forces, but for the ones that we consider working on a box in a macroscopic system like this, they're fairly simple forces. Now we will continue to largely ignore air resistance, which is something that we have done so far with our Kinnah Matics. Simply because, as I said, we didn't have the tools to deal with it. Well, it turns out that we do have some tools that can begin to work with air resistance, but their tools that are insufficient to answer very many questions because air resistance is generally governed by a differential equation, which is mathematics that many of you may not have taken yet. Um, and as such, I will. I will show you a resistance, and we'll talk about extreme scenarios and what it can tell us and how it might affect motion. But we will not do a lot of technical solving using a resistance, and this is very common for introductory physics courses. None of them really cover air resistance in depth, Um, also will use simple models for things like friction that are generally true most of the time, but under specific situations may not be true. So remember that what we're doing here is we're applying simple mathematical models. But the thing you really want to look at is how we do the analysis. Because even if you decide to go farther on and and look at more complex physics courses, the techniques we use for analyzing these systems will be applicable than to, um so we're going to spend the next few videos talking about Newton's laws and what they are and what they mean and how they influence what we're going to talk about. And then we'll move on to our next unit, which will be all about dynamics, that is, to think about systems that are moving in response to forces

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