 Welcome to physics. In this lesson we are going to define what physics is and let you know why it is so important to study. First of all take a look at this cartoon, a classic. And in this cartoon it's showing a fundamental component of physics and that's gravity in the motion unit. Now it also kind of answers the question why do I need to know this? Well just think about it gravity and I would like to say just about every physics principle is really part of your everyday life. Now in order to set the stage for the study of physics, physics what that is, study of matter and energy and motion and forces and how they all interrelate, I thought we would take a look at some key historical figures. So who we have here is Archimedes. Archimedes was a philosopher way long ago, that's a D, and around 300 BCE which is before the common error. In Archimedes he broke motion down into two types. He said well motion can either be violent motion as a result of forces, pushes, pulls or motion could be natural and that would be things like rocks falling or as this picture depicts smoke rising. Well now we're going to jump quite a bit of years and go to our next scientist and that was Copernicus. So Copernicus lived around 1500 and he was very controversial at the time and the reason being is described or shown here in this model. And this is the Helio centric model that he came up with. Helio meaning sun, centric meaning center so sun centered. Now at the time the geocentric model was widely believed. Geocentric meaning earth centered. Geo is earth, earth centered. But Copernicus said the heliocentric model was the valid model that our planets revolve around the sun and the sun is the center of our solar system. Now about 100 years later we have Galileo and Galileo did support Copernicus's heliocentric model. Galileo was around 1600. Galileo also went on to say that forces were only needed to keep an object moving if there was things like friction or air resistance. And what he is famous for, since he was from Pisa, Italy, was dropping cannonballs off the Leaning Tower Pisa. Well if we look here at this picture, I'm not quite sure those are cannonballs. They look like large boulders here but he did drop different size objects from the Leaning Tower Pisa and noted that they hit the ground at the same time. Regardless of their mass they still hit the ground at the same time. Well Galileo really did pave the way for Isaac Newton. Now Isaac Newton interestingly enough he was born in 1642, the same year that Galileo died. And what he's probably best known for Isaac Newton are his three laws of motion and we'll spend a lot of time on those. And also his findings on gravity and gravitation. Well we've probably all heard the story. A young Isaac Newton is sitting beneath an apple tree contemplating the mysterious universe suddenly boink an apple hits him on the head. Aha he shouts or perhaps Eureka. Oh wait a minute that's Archimedes. Oh well in a flash he understands that the very same force that brought the apple crashing to the ground also keeps the moon falling toward the earth, the earth falling toward the sun, gravity. These famous scientists have all set the groundwork for our study of physics. The study of matter and energy and forces in motion how they all interrelate and we are going to begin our study with motion. This interesting sign has Galileo and Newton written all over it. It's showing objects, cow, rocks all falling at the same rate regardless of mass. Now don't worry no cows at all were injured in the making of this video. Now let's consider that poor cow falling off the cliff. He was accelerating and there's different ways to show motion, acceleration, velocities and such and those are by graphs. Graphing is very important in physics and here are showing two types of graphs that we're going to see. A distance time graph and a velocity time graph. Well let's look over here first at the distance time graph and go through each step and see what the graph means. All right let's say we're in a car and we are increasing our distance but the slope is constant so that means steady speed or constant speed going up. And now if we have a horizontal slope on a distance time graph that means we might be stopped. Maybe we stopped to get gas. As we're leaving the gas station we might accelerate out so change our slope here and then we have to put on the brake and decelerate as we come to a stop light. So this graph can show a whole series of motions for a car that I just described. Let's go over here next door. This is a velocity time graph. It also can show quite a bit. Now this blue line here is representing constant acceleration and how I know that is because the velocity is increasing. Stepping on the gas, velocity increasing, showing acceleration. This red line here is also showing acceleration but it's not quite as great as the blue line because the slope is not as steep. Horizontal line on a velocity time graph means constant velocity the cruise control is on and then a negative slope shows deceleration or negative acceleration. So we will use lots of graphing in physics because there are great measure and way to show the motion that's happening. Let's look at one more graph and this is a distance time graph or it's often called position time and position and distance are the same and it really can show what is going on. Now this slope is a uniform slope. Uniform slope it's not changing so it's a constant slope and it says here that slope equals velocity. Well how do we really know that? A line famous for saying that units tell the story so let's look at that. A slope on any graph is rise divided by run and so the rise here the unit is miles so we have miles divided by the run is hours so the slope gives you a miles per hour and that is a velocity or a speed. Now down below here we have simple equations that are basic building blocks in physics you probably have seen these in algebra. Velocity is distance x often stands for distance over time so in this case it's showing 140 miles divided by 2 is 70 miles per hour. Position is velocity times time or we also probably heard that as distances rate times time and it's showing that and it's showing that you how you get how many miles will travel. Now one thing if I could be real picky on this is I'm also a big believer in titling a graph and you typically title a graph whatever's on the y versus whatever's on the x so this graph could be titled position versus time and then anyone looking at this graph could know right away it's a position time graph distance time graph and know what's going to be about so we are going to really use graphing as tools to understand motion and how it works. Well as we end this lesson we really went through a nice historical approach to the introduction to physics a little bit on getting into motion and we're going to center on that in the next lesson and I thought I would leave you with a simulation to do that simulations that stands for physics education technologies are from the University of Colorado Boulder and there's one here that I will post called the moving man and it's a great way to review motion very simple distance time graph velocity time graph and looking at how they change as a man is moving along and it's really quite interesting and a lot of fun too we will be using these quite a bit and I do hope you enjoy it remember my mantra physics is fun I'm like alliteration a lot so physics is fun and I do hope you believe that as well