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Introduction to Units & the SI System

Patrick Ford
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Hey, guys, welcome to physics. My name is Patrick. I want to be your instructor for this first video. We're just gonna talk about briefly units and the S I system of units. Let's check it out. So, guys, what's physics all really about? Well, physics is the study of natural phenomena. That's the definition. You'll senior textbook. But really, it's just a bunch of measurements and a lot of equations. I like to think about physics as a math class with rules or math with storyline. For example, if you take a ball and you drop it towards the ground, it falls to the ground because of gravity. That's a rule. There's also a math equation to describe how fast and how far it falls. And so before we get to the equations, which will see plenty of in the in the future, I want to talk about measurements and units because in nature we measure physical quantities. So things like mass length and time, all the stuff that I have in this table down here that we'll get to in just a second, and the thing about these measurements or physical quantities is that when you measure something you have to have a number and a unit in order for it to make sense. For example, let's say you measure the mass of a box, need a number and a unit to describe it. If you just said that that Mass was 10 10 by itself doesn't actually mean anything. It could be 10 kg or £10 or 10 ounces. So if you have just 10 that doesn't mean anything. But if you measure it to be 10 kg now, that's a number and a unit. And that measurement does make sense now. So kilograms ah, lot of these units will have their shorthand notations. We're going to see a bunch of those things later on in the future. So we're going to see a lot of units in physics. And so, in order for your equations toe work, but you have to remember, is that all the units inside of that equation must be compatible with each other. So the way I like to think about that is they have to speak the same language. And so groups of compatible units that speak the same language or work together form what's called a system of equations and in physics, the big one is gonna be the S I system which stands for in French, the System international. So it's just backwards. So this is the S I system. We've already been supposed to kilograms, which is K G and meters M seconds is s and Newton is n There are other systems that will see the imperial system is an example where we're using pound, feet, inches, seconds things like that. But the main way that we use in physics is the S I system. So physics equations In order for them toe work, they all the units must be compatible with each other. Here's a quick example. One of the most powerful equations you'll see in physics is gonna be force equals mass times acceleration or F equals m A. So if we replaced all these variables with their units, we can see that a newton is equal to a kilogram times acceleration. I'm just gonna give this to you. Acceleration is in units of meters per second squared. So notice how all of these units here Newton's kilograms, meters and seconds all belong to the S I unit system. Whereas if I said a Newton equals a pound times a meter per second squared. This is actually incompatible, whereas this first equation is compatible. So this is actually incorrect. And you're gonna get a wrong answer if you start mixing and matching things from different systems. So make sure that all your equations and all the units speak the same language and are compatible. Alright, guys, that's really all there is to it for this one. Let's move on to the next video.