01 - Introduction to Physics, Part 1 (Force, Motion & Energy) - Online Physics Course

hello welcome to the physics 1 course unit 1 this lesson I'm gonna title it introduction to physics so what I want to do in this lesson really is spend the next 15 20 25 minutes however long it takes to give you number 1 a motivation for why you even should care about learning physics I mean some of you may have to learn it but why should you care to learn it but secondly and what we're mostly gonna be doing here is giving an overview a broad overview of almost every topic in physics which seems to be an insurmountable task but we're gonna take kind of a tour of the main concepts and the main ideas in physics to give you kind of a roadmap of what we're gonna learn in this entire class alright so at the end of this lesson you should know not only why you should care but you should also understand some basic ideas about what is physics what do we care about and why do we learn it and what main topics are inside of the the class that we call physics so the first thing is physics is all around you it's one of the sciences the sciences that you can walk outside get bathed in sunlight drive down the road in a car whatever and you are experiencing physics and almost everything you do things like light hitting you on the skin heat radiation from the Sun electricity magnetism radio waves motion the work that that is done by the car from the gasoline and the engine pushing the car all of that stuff is physics so one of the main reasons why you really should care about learning it is because literally everything you do every second of the day is impacted by physics but I personally want to convey to you the big picture of why you should learn physics and why why maybe you should take an interest in it and that is because for hundreds of years really thousands of years humans have been trying to understand the world we live in we don't have all the answers even even in this physics class we don't have all the answers but we have amassed a great deal of knowledge about how things work so I want you to kind of think about two or three hundred years ago when there was really no electricity and you're in your lab or in your house and your was candles burning and you were just struggling as some person and through 200 years ago did you understand what magnetism was or to understand what a chemical reaction was that's more in the realm of chemistry but you know chemistry and physics are like peanut butter and jelly or if you were trying to understand what heat really was and how what work really was and what energy really was and you spent your whole life trying to understand those things and scribbling down equations and going down one dead-end and coming back to try to try a new path right so you would for lack of a better word you would do almost anything back then to understand what you now have the opportunity to understand because of all of those people that came before you and devoted their lives to try to figure this stuff out one example would be Isaac Newton I know you've heard of Isaac Newton we're gonna talk about Isaac Newton for a long time in this class well you know that he has is his famous laws of motion what you may or may not know is is Newton is the guy that invented something we call calculus today which is an advanced branch of math right so this is a person that was trying to solve a problem and instead of just giving up because he didn't know how to solve the problem he invented the entire concept of calculus the thing that everybody learns takes many years to learn he invented that himself for the purpose of solving a problem he was working on right but even Newton as smart as the man was as brilliant as the man was would probably do almost anything in his day to have the knowledge that you have today because of everything that Newton did and everybody that came after him contributing to this knowledge he probably would just dream that you could watch a video or take a class or solve some problems and learn all of this stuff in all of these topics that I talked about magnetism heat you know and then the more modern things like relativity and quantum mechanics so what are my expectations in this class what do we want to get out of it I want you to be able to solve problems I'm definitely going to lecture and I'm going to tell you the concepts concepts are probably the most important thing but equally important with that or maybe even more important than that in my opinion is to be able to solve a problem like you can understand the concept behind something but if you can't get your pencil out and you can't solve a problem then you really don't understand anything really in my opinion so this this whole class is going to be problem-based we're going to lecture we're gonna get concepts on ideas but we're gonna put pencil to paper and we're going to solve problems so my advice to you is to keep in the back of your mind everyone these concepts are easy to understand I can explain every concept in physics to probably a third grader as a basic overview but solving problems tends to give students a lot of prop a lot of problems because their math skills might be okay their concepts they might understand the concept but putting the two together reading a word problem figuring out what is important in the problem writing down whatever equation you're trying to use and applying it correctly and is is very hard and the reason it's hard is because it takes practice just like you know running a marathon takes practice or learning how to you know play basketball or football takes practice solving physics problems really just takes a lot of practice but once you do it you will definitely get better at it so my advice is as we solve our problems here please watch me solve it make sure you understand it but then pause the lesson and get your own paper out and solve it yourself even if you've just seen me solve it just a minute ago you going through the motions of solving the problems is definitely gonna help you and the final thing I want to get to before we get into the overview of physics is that anybody can learn this stuff anybody okay the only thing required is the willingness to learn and some basic math skills and when I say basic I mean you're gonna have to know some basic algebra which I will review along the way for the most part but you'll need to know some basic algebra some basic trigonometry we'll talk about angles and triangles I'll try to review as much as I can but you really should have some basic skills in those areas and ultimately you need to be able to put in the effort to solve problems yourself even after you've seen me solve them the final thing I want to talk about before we get into the overview is that we don't have all the answers we're gonna present all of this stuff as if humanity has figured everything out but I want you to know that we haven't figured it all out I'm telling you right now people are doing research in advanced physics trying to figure out what masses you know this marker has some mass right we say it has mass you all have an idea about what masses but people are doing research today trying to figure out what really is mass right why is it harder to push something that has a lot of mass why does that happen how does the universe know to kind of resist your pushing whenever it's a big heavy ball or a boulder and I can push something that has less massaman we take those things for granted but the physical mechanisms that underlie all of the stuff in reality is not trivial it's not something we all know the answers to so as you learn on this stuff learn it but keep in mind that as you kind of get older and you study more there's always going to be more stuff to learn and more stuff to contribute all right physics in general can be broken up I'm going to break it up into three main things there there's physics typically you take physics one and then there's physics - and that's physics three right so what do we cover in physics one I'm gonna expand on this stuff you know over the next several minutes but in sensually physics one or all of the concepts associated with motion motion force and energy now everybody watching this has some idea of what motion is things that move right and what a force is when you push on something right and energy might have an idea of energy but that's usually a little bit sketchy or people aren't quite sure what energy is but we know it has something to do with motion or with doing something that kind of thing and that's typically true but the idea here is we're gonna drill down into these areas and we are going to a hundred and ten percent go into every one of these topics and define them to understand what we mean in physics by force motion and energy so that when we solve our problems we know what we're doing with each of our equations with each concept now typically after you finish all of this up which is quite a bit of material we're gonna get into more detail about that second you talk about physics - and these are arbitrary definitions but typically in physics - you learn about a big word that scares a lot of people it's called thermo what do you think thermo means it's like a thermos it means heat right or temperature thermo dynamics woops I can't spell dynamics dynamics right thermodynamics and waves so when the broadest sense physics - is going to be about dynamics means changing thermo means heat or temperature so it's all about things that are changing temperature changing heat and also what kind of work can we get out of that so you think about a car engine you combust gasoline in the piston right or in the piston chamber that explosion releases heat and it pushes that piston so the concept of heat which is coming from that explosion right and the concept of the piston moving which is doing work which is doing work able to push the car those are interrelated things so thermodynamics is all about heat energy how do we transfer that into work that we can do in the environment how can we build a machine that somehow uses heat energy and get it to do some work and there's a lot of details there that we'll get to that's what it basically is and we talk about waves you know we have waterways we have sound waves we have energy that we can transmit via a wave you know if I get a jump rope and I kind of oscillate it I can send energy down the rope to impact a wall or whatever it's tied to so we're gonna talk quite a bit about waves and then we break up the class into physics three physics threes actually my favorite part physics but I like them all but physics three is my favorite part and that is electricity and magnetism so electricity and magnetism there's some other topics in here now when I say electricity we are gonna learn a little bit about electric circuits you know batteries circuits voltages you know current electric current things like that we're gonna talk about that but really the the main part of electricity and magnetism we're gonna learn about magnets we're gonna learn about the magnetic field that surrounds a magnet we're gonna learn about the electric field that surrounds an electric charge like an electron or a proton or some other charge particle so we have this thing called electricity electric fields and magnetic fields and they're kind of like peanut butter and jelly they're not exactly the same thing but they're definitely related and the equations that govern both are very similar to one another so really in modern physics we've unified electricity and magnetism into one thing called electromagnetism and it turns out if you take an electric field on a magnetic field and you oscillate them so that they're kind of a combined oscillation what you end up getting is an electromagnetic wave so it's a wave that travels that has an electric component and a magnetic component and it travels and guess what that is that's light so I have lights here they're hitting me they're bouncing off of me they're going into the camera those are all electric magnetic fields that are oscillating hitting me and bouncing off so we're gonna talk about the wave aspect of light after we talk about electric fields and magnetic fields right and then this is kind of you could call it physics for but I'm gonna call it modern physics which is something you typically see also modern physics and this is actually one of my favorite parts also because I just find it mind-blowing the first part of this typically is relativity I'm sure you've probably heard about this and I know that you also probably heard about something called quantum mechanics what is all this about relativity deals with the fact that's just mind-blowing but the fact that clocks you know things that we think are constant tick tick tick tick of a clock time is not constant for all people when they're moving near the speed of light so if I if I have one clock stationary and one clock stationary next to it they're ticking and synchrony right and then I take one of those other clocks and i zoom him off near the speed of light when that clock is traveling near the speed of light time doesn't flow the same for that clock or that person in the spaceship it flows differently though in other words the reason it's called relativity is because things happen differently to different people or different experiments depending on how you're moving how fast you're moving now we don't notice clock's ticking differently because we're not traveling anywhere near the speed of light we're traveling at a snail's pace but that's the way the universe works everything's relative including the ticking of clocks and then we have the idea of quantum mechanics which we're going to get into a whole lot of detail later but quantum mechanics is all about the fact that I told you electromagnetism was a wave right but we also have figured out in the 20th century that it it does behave like a wave light does behave like a wave but it also kind of behaves like a particle like a like an object instead of it has characteristics of wave but it also has characteristics of being a little particle so is it a particle or is it a wave it turns out it's both we don't have a word for it but real photons real electrons real protons real tiny particles of anything have wave-like characteristics and they also have particle like characteristics so it kind of messes with your mind because it doesn't make sense but it is the way the world works because we have over a hundred years of experiments showing that both of these things relativity and quantum mechanics are both as far as we can tell absolutely true now what we want to do is jump a little bit more detail we're gonna get in the entire course into so much detail solving tons of problems but I want to give you a road map to show you a little bit more about these topics and we're gonna get in and get a nice overview of that so when we talk about motion first thing we're gonna actually talk about in physics are the equations the equations of motion and to simplify it further we're gonna actually talk about motion only along one direction one dimension we call it so we're not going up and down we're only going left and right because it makes things simpler first so you'll see 1d motion you'll see have 2d motion when you have like a like a throwing the ball up in the air and also horizontally and then of course we have 3d motion which is the real world you know when things can move left right up down backwards and forwards but really the equations are all very similar so we start out by talking about what happens in one direction only one that the object can only move basically backwards or forwards and I'll tell you this thing called equations of motion scares a lot of people but you already know a simple equation of motion and that is what what do you know about velocity I know we haven't really talked about velocity in this class we're gonna talk a whole lot about velocity but you already know that in a car when you're driving it's it's miles per hour right or kilometers per hour right so the velocity that you're traveling is the distance over the time how far did you go how long did it take you divide those numbers you get something call a velocity now if you remember a little bit of algebra this is a fraction so I can actually get rid of the time on the bottom by multiplying left and right hand side of the equation by time so on the left hand side I can get velocity multiplied by time and on the right hand side that will be just distance which is left over now if you don't totally understand how I got there this is just a little bit of algebra I multiply the right-hand side by time which cancels time to time leaving distance I multiply the left-hand side by the same thing time so I have velocity times time this equation makes sense also because when you think about it if I know that I'm traveling down the road at 45 whoops 45 miles per hour we don't typically use miles in physics we're gonna learn about meters and all that but if we're going a speed or a velocity of 45 miles an hour and I'm traveling down the road for two hours how far did I go think about it I'm going 45 miles every hour and I'm multiplying by the two hours because you know every hour I go another 45 miles so that should be clear that this is 90 miles that I've traveled this thing here distance is equal to velocity times time that's just a very simple equation of motion so don't let these words confuse you or scare you equations of motion and sounds really difficult but you already have experience with basic equations of motion you know that the distance you go is going to be how fast you go in times how long you're traveling at that speed how's the time involved so what we're gonna do is we go on is we'll just have more complicated cases we're gonna figure out well what's gonna happen when I have gravity involved from dropping something what's gonna happen if I throw something what's gonna happen if I have friction right then the equations of motion are a little more complicated but it's the basic same idea so for instance in 2d motion in 2d motion I might actually throw something like a baseball or something I might throw something up here at like 39 meters per second so I'm using the same thing it's a velocity but it's meters instead of miles meters per second so you all know that if I take a ball and I throw it at an angle right so let's say I'm throwing it at some angle here I'm gonna call that angle theta that's just a variable that's talking about the angle or I can just take out the variable itself and just say well I'm tossing it 25 degrees from the ground right what's this thing gonna do I mean you all know that if I do that it's gonna continue up it's gonna hit some maximum and then it's gonna come down and it's gonna hit the ground again so the question is if I throw a ball at 39 meters per second at a certain angle what do I want to know typically I want to know how high did it go that's what I want to know how high did it go and I want to know generally how far did it go and I'm not gonna write it on the board but I also probably want to know how long was it in the air so that's called projectile motion or 2d motion and it's just gonna be basically an equation of equations of motion applied to that situation right now what we're gonna actually do to solve these kinds of problems is we're going to take this 39 meters per second I'm gonna blow it up for you down here if I throw something at an angle of 39 meters per second right and I'm throwing it at some angle relative to the ground 25 degrees let's say right here it actually is kind of complicated to deal with 39 meters per second at an angle right at all at once so what we typically do is we actually break a 39 meters per second at that angle we break it up into two parts we break it up into how fast is it going horizontally right the horizontal part of the motion and how fast is it going up and down the up and down the vertical part of the motion so I might have as a result of this I might have a vertical part see it kind of comes over to where the tips of the tip of the arrow is so this is going to be a vertical part of that motion and this is going to be a horizontal part of the motion so what I'll do is I'll apply the equations of motion which we'll learn later to the up and down motion by itself and then to the horizontal motion by itself because anytime you throw anything if you throw it steep if you throw it shallow you can always break the motion into horizontal motion and vertical motion so it's easier to solve these problems by solving the horizontal parts separate from the vertical part so we're gonna learn about that in this concept here splitting it up like that that's called a vector and we're going to learn about vectors in great detail because they're gonna be one of the big tools that we use in our tool bag to solve problems now the next thing we learn in physics typically is the concept of energy and I know that most everybody here has an idea of energy but we're going to talk just to just a brief minute about energy so the best way I can describe energy is or at least one type of energy is a rollercoaster so here's a rollercoaster a very high hill and then comes down to the bottom and then a little bit like this and then maybe it just kind of does something like this so there's a Kharak cling cling cling cling cling gets to the top very very very high right at the very top of this very high mountain right we say that it has a high potential energy high potential energy I don't have room to write out potential energy but the reason it has potential energy at the top is because we're in a gravity field so if you bake something very high off the ground if you were to drop it it has a high potential to to accelerate down to the ground and to hit the ground right so to do to do something they hit the ground they have to do some impart some energy into the ground so we say has a high potential energy here so what happens is the roller-coaster goes to the very bottom and all of that potential energy you have because you're accelerating when you get to the very bottom here when the roller-coaster starts to round the bottom down there we say that we have a high kinetic energy so we're going to learn a lot about potential energy and kinetic energy kinetic energy is how fast you're moving it's the energy of motion so you know when you get to the bottom of the hit of the of the trough here in the roller coaster going fastest up here you're going slow so you have very low potential energy here I mean it's our high potential energy here and it's all converted into kinetic energy and then here over at this part what do you have when you have medium potential energy because you are a little higher off the ground but not as high as here and you have medium kinetic energy because you're not going quite as fast as you were down here you bleed off some of the speed so one of the big big big big big big big things we're gonna do in physics is we're gonna talk about the total energy of a system and the total energy of a system of that moves like this any way you the potential energy plus the kinetic energy and the total energy of the system actually doesn't change because whatever I start the system out up here at the top is how much energy I have it's just all in potential energy form so at the very top of the hill I have a very high potential energy that's what the up arrow means and I have a very low kinetic energy up at the top here but then when I get to the bottom here I have a very low potential energy because I'm basically a ground level and I have a very high kinetic energy because I'm going really fast so you see what's happening every time the potential energy gets high my kinetic energy must get low and every time the potential energy gets low the kinetic energy must be high so it's like a trade-off I'm basically it's like two cups of water I'm pouring the water in here now the energy is over in the potential energy cup then I pour some of the water back in over here now the energy is all in this cup and if I pour half in half I have half of my energy in the potential energy Cup and then the kinetic energy cut that's basically here so the trade-off between potential and kinetic energy can be used to solve tons of problems and we're gonna spend many many hours solving lots of problems involving potential energy and kinetic energy okay it's one of the big central core topics of physics then we're going to talk about the concept that I know you've heard about Newton's laws whoops let me go to spell Newton correct Newton's laws Newton's laws of motion so what Newton's law says basically is well there's a few laws of motion we'll talk about all of them but the big fame the one that we're gonna use to solve tons of problems is F is equal to Ma so this is the force on something is equal to the mass times the acceleration what this thing says in layman's terms is that if I push something with a force like if I push something then it every has mass obviously because it's made of matter if I push something then it must accelerate that's all it says it's common sense you know this stuff I mean physics seems really difficult but you know this you know that if you push something it's going to accelerate if I have a bowling ball and I'm forcing it I'm using my hand to him part of force then it's going to leave my hand in motion and as I push it from rest it's going to have to accelerate which means it's gonna speed up from some non moving velocity up to some speed right so this F equals MA I'm going to be used to solve a great-great-great too many problems and then after we talk about Newton's laws for a while and solve tons of different types of problems we're going to talk about Newton's law of gravitation which is a really big deal obviously because we live on earth and there's gravity here what does this mean though if we have a planet we're gonna call it earth and we have a moon here we call M so the earth has some mass we call it m1 and the moon has some mass and we call it m2 what Newton figured out is there's a force that exists between any two pieces of matter it exists between you and your pencil it exists between a lamp and television it exists between the Earth and the moon any two pieces of matter pull on each other with some force of gravity and that force if the distance between these two things we call our that force of gravity is equal to some constant number G which we'll talk about it's called the gravitational constant time mats one times mass 2 through multiplying all the masses together times G this number and on the bottom it's the distance between them but squared so you might hear this called the inverse square law or something like this so if the Earth's mass gets bigger m1 then the force is bigger if the moon's mass gets bigger the force is bigger but if we increase the distance between them like if we stretch out the earth and moon even bigger than since it's in the bottom we're dividing by a bigger number so the force actually goes down as we make things get farther and farther apart so this is called the universal law of gravitation now we all actually know now that Einstein 100 couple hundred years later released and invented his theory of gravitation and his theory of gravitation is actually more correct than this one but still this is a really good starting point to understand gravity and we're gonna solve lots of problems using Newton form of gravity because it's a whole lot simpler than Einstein's theory of gravity which is beyond the scope of this class but just keep in mind that you know this was accepted fact for 250 years or so and now we know that it's not quite right in some cysts in some instances and in the early 1900's Einstein published a theory which totally reinvented how we look at gravity completely but you might ask yourself if if I push on something it's gonna accelerate then if there's a force between the Earth and the moon here shouldn't the moon come crashing in to the earth shouldn't it come crashing into the earth well of course it should absolutely and that's the famous thing you know Einstein Newton sitting sitting under the tree and watching the Apple fall and having it who knows if it's true or not that's the story right he realized that the earth is pulling on the Apple and the Apple falls down he realized maybe the earth is pulling on the moon with the same force well then why is the moon not crashing down like the Apple that's the real question but he thought well maybe it's possible that gravity is extending all the way to the moon and pulling on that and the answer to the question is it is pulling on the moon and if the moon were not moving it would crash into the earth however the moon is actually moving it's moving sideways with some very high velocity V so it's going around and around and around it is being pulled in but it's going so fast in that horizontal direction for lack of a better word tint that it's called the tangental direction then it never really hits the ground and you think how is that possible well I have a little prop here it's not a great prop but it's a little prop so this is like this is like the moon here on the end of my little wire well if I take this guy and start spinning it around what happens here well you see it's going round and round and round around just like the moon is but what am I doing with my hand in the center look carefully I am actually pulling on this thing so what I do is when you start it off you have to give you have to start swinging it right like I'm swinging and then I get it to go around once and then I go it go twice and then I then once it's going horizontal like this I'm pulling on it I'm pulling it straight into my hand but it never hits my hand because I've given it a very fast speed horizontally like this and that's basically the exact same thing happening with the moon if the moon weren't moving at all if it just stopped then it would accelerate straight down and hit the earth but only because it's moving so fast horizontally can we escape that okay now we talked about gravitation right Newton's law of gravity and then after we talk about gravity we talk about collisions collisions and physics and what do I mean about it could by collision I'm saying what happens when you smash two things into each other like let's say I have some mass M sub one and I have another mass over here M sub two I don't know what the masses are but this could be five and this could be 25 or something could be different right and then this thing is going this direction at some velocity v1 it could be like 100 meters per second or something and this guy's going in the opposite direction v2 and it's a different velocity so different masses and different velocities they smash into each other well what's gonna happen when they bounce off what is the velocity of this guy gonna be when it bounces off what's the velocity of the other one gonna be and which direction are they gonna go and what if I don't smash them head-on what if I smash them at an angle so that they fly off at an angle you know like billiards or a pool table so all of this stuff has to do with collisions which involves the concept of momentum so we're gonna learn how to calculate the momentum of this ball and the momentum of this mall and we're gonna use a law of momentum to figure out what's going to happen after the collision so that's basically wrapping up what we generally talk about in what we call physics one now I told you physics two was what we call thermodynamics and waves thermodynamics and waves and so what we're gonna do is talk about that briefly next

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Keywords: introduction to physics, intro to physics, physics, physics 101, online physics course, force, motion, energy, kinetic energy, potential energy, momentum, physics 1, physics 2, physics 3, college physics, physics lecture, introduction, ap physics, newtons laws, physics tutor, physics tutorial, tutorial, science, newton, gravity, college, introduction to physics 101, physics basics, online physics, physics course, high school physics, learn physics

Id: i_CijGuk7fw

Length: 30min 40sec (1840 seconds)

Published: Tue Aug 28 2018