8/12/2019 1 - 2 - Week 1 Video 2- What is Energy- And Why Do We Need It

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1 - 2 - week 1 video 2- what is energy- and why do we need it-.txt[MUSIC]In this video I'd like to introduce a fewbasic terms for defining energy.And, while we're going to spend some timetalking about a few of thesedefinitions in detail, though I promise itwill be very limited detail, what I reallywant you to take away from this video isthat in themost essential sense energy is simply thecapacity to do work.Now sometimes you're going to findliteraturethat refers to three different kinds ofenergy, I personally feelin a sense that conflates the definitionof energy with the term energy.So, instead what I like to keep sort ofseparate iswhat energy is and the kinds of work thatit can do.Energy can do mechanical work, it can dothermal work and it can do electricalwork.Mechanical work refers to displacement ofmass.So for instance, if you kick a soccer ballthen you areexerting some energy to move the ball fromone point to another.Displacement of mass requires applying aforce over some distance.And so if you recall some of your unitanalysis from, your elementary physicscourses, force can be further decomposedinto the product of mass and acceleration.So, the capacity to do work is the product

of massacceleration and the distance that you'regoing to move that mass.So for example, when the measure, the,let's saymost universal measure you'll hear used isa joule.A joule is defined as a newton meter.And a newton, if you recall, is akilogram, meter per second squared.So that's the amount of force applied overa meter is referred to as a joule.Thermal work I like to think of asdisplacement of atoms just because I thinkit'suseful to keep these concepts, straight ifyoucan think of them in some kind of parallelsense.So where as mechanical work is displacedat amass think, about thermal work as adisplacement of atoms.Displacement of atoms simply means you'resortof agitating and exciting atoms for, for

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1 - 2 - week 1 video 2- what is energy- and why do we need it-.txtinstanceif you are cooking, you're basicallytakingenergy to transform the object that you'recooking.You know atoms become agitated or movewhen heat is applied and the,measure, that we may all be familiar withfor heat is a calorie.A Calorie is defined as the energyrequired to increase thetemperature of a gram of water by onedegree Celsius, specificallyto increase the temperature of a gram ofwater from 3and a half degrees Celsius to 4 and halfdegrees Celsius.So, this, by the way is also known as asmall calorie which is only,is concept, is, is just a little bitdifferent from a food calorie.When we think about food calories we'rebasically thinking about 1,000 smallcalories, but a calorie is just a, measureof energythat is, doing thermal work.And it is equivalent to, just over 4Joules.So a joule is about a quarter of acalorie.[BLANK_AUDIO]And whereas mechanical work isdisplacement ofmass, and we think of thermal workas displacement of atoms, electrical workwecan think of as displacement of electrons.

When we apply a magnetic field to acircuit, we induce electrons to travelthrough that circuit.So that is the, the work being done toinduce those electrons to travel is, orto move is, is electrical, is the energyapplied to do electrical work.One joule is the amount of energy that caninducean amp through an ohm of resistance forone second.[BLANK_AUDIO]So you, as you read and, and work invarious fieldsin energy you're going to come across lotsof different terms.And all you have to do is, is keep in mindthat idea of, work being moving something.Moving either electrons or, or atoms to,thatrepresent heat or, that movementrepresents heat or mass.So you may, come across this term joulebut you'll alsocome across terms like horsepower-hour ortherms or calories or kilowatt-hours.

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1 - 2 - week 1 video 2- what is energy- and why do we need it-.txtAll of these are just referring to amountsof energy, but they're just implicitlyreferring to some specific type of workthat the energy is being used to do.But what I really want you, as Imentioned, to take away fromthis course, is the idea that energyrepresents the capacity to do work.So consider, for example, one of ourancestors.And if our ancestor was fortunate theywould come acrosssome objects like food, that they couldbasically consume to acquire some energy.In this case, in the form of calories.And, of course, if they're going tosurvive, they hopefully are going to findanopportunity to expend some effort, do somework, to acquire more of those calories.And that really is, is the cycle I wantyou thinking about.Now of course you can imagine in asituation ifthey're able to get more energy from theirconsumption of calories,then they need to expend in work toacquire replacement calories, thenthey're going to have extra energy to doother things.Maybe build a shelter.Maybe play with their children.Maybe create some kind of art.You know, so they'll be able to use thatenergy and consumption activities as wellas production activities.But I, I, I like to think about this in

this very most basic andessential sense, because it, itunderscores just what abasic need energy is for our every kind ofactivity we can think of.[MUSIC]

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