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Current time:0:00Total duration:10:57

Video transcript

let's talk about one of the most fundamental ideas in science and that is the notion of energy and energy definitely has some meaning in our everyday life if we kind of imagine things that are moving or hot or bright as being energetic but what I want to talk about in this video is a more formal definition of in a more scientific definition and the most typical one that's often given is the ability to do work ability to do and I'm going to put work in quotes because the notion of work here isn't the everyday notion of work where you go to your job and you work 9:00 to 5:00 and you get paid work in a physics context is a little bit it's not completely unrelated to our everyday notion of work but I'll give you an example just to get a better idea of it so let's say that you have some object here and you were to apply a force you were to apply a force in that direction and the magnitude of that force let's say it's 10 Newtons and if the if the units Newtons and force isn't too familiar to you don't worry too much but you can also review it on those videos on Khan Academy but you apply a force to the right on this object and by doing that you're able to move the object you're able to displace the object in the same direction as that force so you're able to displace it let's say 10 10 meters so after you've done it the object the object is right over here so when you do this you apply a force and you're displacing and that's causing the object to be displaced in the direction of that force you would say that work has been performed and the amount of work that has been performed would be 10 Newton's times 10 meters and so 10 times 10 it would be equal to 100 and then the units are Newton meters of work 100 Newton meters because you're multiplying Newton's times meters of Newton meters of work and newton meters that has been defined as the Joule which is the unit of work and also the unit of energy so this is the same thing as 100 I could write it out joules 100 joules or we can just abbreviate it with a J so 100 joules of work has been performed here by moving this we've done we've taken so we've done something here and this is considered to be work 100 joules of work if we move this twice as far then it would be 200 joules of work and so energy is the ability to do this type of work now let's look at let's look at these pictures here which are depicting different forms of energy and let's see if we can identify the forms of energy and then think about how they can relate to actually doing work so if we look at the fire here there's some may be obvious forms of energy we have some thermal energy it's fires are definitely hot so thermal energy but we should think about what is thermal energy fundamentally a systems temperature is really about the average kinetic energy of its molecules so thermal energy is really about the energy of movement it's really about all these little molecules here because of the combustion reaction going on they're getting excited and they have higher kinetic energy and so the temperature goes up their average kinetic energy goes up so thermal energy is really a form of energy due to movement and the general term for energy due to movement is kinetic energy so thermal energy is really a form of kinetic kinetic kinetic energy you also have light being emitted that has energy as well we call that radiant energy so that light being emitted that's the reason why we can see this fire radiant radiant energy now you might say okay maybe that's all of the energy in the system but I'll say no there's another form of energy and actually even in this picture that's probably where most of the energy is and that's potential energy so where is the potential energy well it's it's sitting in the bonds of the fuel over here so these are either chips of wood or charcoal of some kind but these are formed by carbon-carbon bonds so you have these carbon-carbon bonds and they could be bonded to other carbons or other other things and they're also going to be bound to some hydrogen's here and there so you're going to have you're going to have bonds like this that actually store energy in them they have the potential to be released if you're able to break these bonds those electrons are going to get into a low energy state or they might bond with other things and in the process they're going to release energy that's going to be radiant energy and thermal / kinetic energy so how does this happen how do these bonds how do these bonds actually get broken well that's our good old friend the combustion reaction that's our good old friend the combustion reaction where you take some you take some oxygen you take some heat or we could say some energy so it takes a little energy to get started that's why you might have to light this with a with a match to begin with so oxygen plus energy plus energy and then you could say plus these carbon carbon bonds and we could say plus you know whatever it is these fuels which are made out of carbon or either charcoal or wood so plus all right I'll do it like this I'll draw some carbon-carbon bond right over here that's going to combust and I'll do this in a color so that is that is going to really having trouble changing colors this is going to combust combust and it's going to release it's going to release water because these the fuel has hydrogen's in it it's going to release carbon dioxide and it's going to release a lot more energy I'll do that in caps it's going to release a lot more energy and that energy we see we give in the form of the kinetic energy of the molecules and the radiant energy being emitted now you might say okay I can buy that I have this potential energy here and this potential energy that's in the bonds of these of these between these atoms we call that chemical potential so we have chemical chemical potential energy potential potential energy is right over there but you might say okay I buy that the chemical energy is being converted to into the thermal energy and the radiant energy and this is actually an interesting point energy this is a law of conservation of energy energy cannot be created or destroyed it can only be converted from one form or another but you might be saying okay I can convert from one form to another but how can this actually do work in the way that I've even depicted here well the entire industrial revolution is all about trying to convert from one form of energy to another and also to do work so a steam engine is fundamentally based upon combustion heating up some steam and then that steam can expand and then it can push a piston to do all sorts of things including move a train combustion is what's going on in your car engines where the Pistons are expanding due to the due to the thermal energy and then that helps drive the drivetrain of the actual car so it can clearly do work so here we have some other examples this is lightning and so when you see the Lightning there's something clearly very kinetic is going on you have electrons you have electrons moving from the cloud from the cloud to the ground and you might say so this this right over here that is you could say that's kinetic energy kinetic kinetic energy you might say well how can I do work with that well that's what the whole electronics industry is all about that's what power lines are all about movement of electrons that's current and current can be used to do all sorts of amazing things you can actually have an electric motor is one way to actually do it so that's kinetic energy there there's clearly radiant energy going on we can see the lightning and that radiant energies do because the air gets ionized and gets heated and so there's also thermal energy as the electrons go down there's heat that is actually being generated now where did where did this energy come from it just doesn't come from anywhere well you have all this potential energy that starts that starts building up in these clouds as the water vapor rises and the mechanism isn't isn't fully understood of how this happens but because of energy from the Sun you have water vapor rising as the water vapor Rises through the clouds the the neg the bottom part of the cloud becomes more negative it becomes more electron rich and the top part of the cloud become more positive and so you have these electrons that really want to get down here and then the ground because the the air above the ground becomes more negative the ground starts to becoming more positive and so you can imagine these electrons more and more want to get down here but this air isn't a natural conductor but once the electric potential gets high enough these electrons find a way the air essentially get ionized is in the Tron's are able to find a path so while this is all building up you have this electrostatic potential building so this is electro static static you can't see that that well electro static potential and how this forms once again so it's an area that people are still there's some good theories out there about how this forms but it's not a hundred percent well-established and over here in this third old drawing of this person doing a handstand dive this is probably the most the most typical example of potential energy being converted into kinetic energy that you might find in a physics textbook over here at the top of the diving board this gentleman has potential energy by virtue of his position and over here it's very clearly has the potential to fall and it has a potential to turn it into kinetic energy and so once he falls over at this point most of his potential energy has been converted into kinetic energy so here it's potential here it's potential and here it is kinetic kinetic energy so the big takeaway is energy it cannot it's the ability to do work it cannot be created or destroyed but it can be converted from one form another and all of the forms at the end at their essence you can really think about them at in in two big buckets you can think about them as potential energy or kinetic energy or or or kinetic energy and as the last example you might say well how can this guy do work well you can imagine if there was some type of system here you system here where you know we'd create some machinery maybe there's a pulley right over here and then and then it's lifting a weight right over here well if he jumped on this you won't fall down as fast but then if as long as he's heavier than this weight it's going to pull this down and then this weight is going to go up so he has the potential to do work by virtue of his position there just isn't this pulley system there to to get that actual work done
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