Program 20 - "Temperature and Heat"

MusicSilico: "We are back with Science 122, the Nature of Physical Science.This is the only telecourse with central heating and cooling.This is Program 20, Lesson 3.5, Temperature and Heat."Before we're done with this program we will have identifiedtemperature in both qualitative and quantitative terms as welearn how temperature is measured through the use of different temperature scales.Then we'll explore the relationshipbetween temperature and heat through the concepts of specific heat of substancesand the latent heat of phase transformations.We'll conclude with a brief study of heat transferand the physical aspects of heat and life processes.Here are the objectives for today's lesson.These objectives are also in the Study Guide at the beginning of the lesson.Before you begin to study the lesson, take a few minutesto read the objectives and the study questions for this lesson.Look for the key words and ideas as you read.Use the Study Guide and follow it as you watch the program.Be sure to read these objectivesin the Study Guide and refer to them as you study the lesson.Focussing on the learning objectives will help youto study and to understand the important concepts.Compare the objectives with the study questions for the lessonto be sure you have the concepts under control.

Fire is probably the oldest technology known to man.It's use certainly began long before history.In Greek legend it was Prometheus who stole firefrom the gods and gave it to men.It was a mistake for Prometheus to do this from the Greek perspective.There's more to the study of heat and temperature than just fire though.Fire is the obvious part of it, and, of course,fire was one of Aristotle's elements.But we are very sensitive as a species to changes in temperature.Now, you got to consider that earth has a very narrowtemperature range, and that life, in general, is extremelysensitive to small changes in temperature.In fact, the location of our planet and surfaces processes like thatatmosphere and the oceans keep the temperature relatively constant.

Now those of you who have been in really coldweather in glaciers and things like that may notconsider it constant, but when you consider therange of temperatures encounteredin the universe from nearly absolute zeroto temperatures of tens and millions of degreesin the centers of stars, the 50 or 60 degreetemperature range thatyou encounter on earth isreally quite small.Climatic changes, in other words, changes in this temperaturehave been a major factor in biological revolution,and no doubt, responsible for man's preoccupation with fire.I mean, let's face it, if all evolution had taken placein tropical climates where it was always warm, the ideaof discovering fire might not have been so important.We also know that climatically speaking very small changeshave very large effects, and we, as a species, are not reallyvery well adapted to temperature changes.In fact, of all the species on earth, at least mammals,we're probably less able to deal with wide rangesof temperatures than almost any other animal.

We have a special sensitivity to temperature, for instance.In fact, most people can walk into a room or from one roomto another where the temperature is only four or five degreesdifferent and feel a very radical temperature change.So, because of this, the control of temperature and the conceptof heat and fire and so forth has always been a majorpreoccupation in terms of making clothing, making fires, makingheat resistant dwellings and cooking and that sort of thing.The Greeks as scientists learned very littleabout the properties of heat and temperature.In fact, Aristotle had not much to say about it all except that heconsidered fire to be one of the basic elements.And heat and cold were basic qualities of matter, you may remember.

Our modern concept of temperature beginswith the invention of the thermometer by Galileo.His thermometer was an air thermometer which also,unfortunately, recorded changes in atmospheric pressure.And it wasn't really a very good thermometer.But the idea that you could attach a numeric relationship or attacha number to measure the subjective, qualitative thingwe call temperature, is a major breakthrough and it's not toosurprising that it would be Galileo who would make this breakthrough.It's not actually clear that Galileo invented the thermometer,but he's the first one to write about it.So what is temperature, anyway?Everybody knows what temperature is.Temperature is what you read off a thermometer.But what if you didn't have a thermometer?Would you still know what temperature is?This is our problem with temperature--is that it'sactually subject to our perceptions.It's a relative sort of thing.

Suppose, for example, that you put one hand in hotwater and one hand in cold water.And you leave them there for a few minutes until yousort of get used to it and then you take both handsand plunge them into lukewarm water.You think the lukewarm water will feel the same temperature?Of course not.The hand that was in the warm water will feel the lukewarmwater as cold, and the hand that was in the cold waterwill feel the lukewarm water is warm.I'm sure you've had the experience, also, of one of these cold wintermornings, although it doesn't get that cold here in Hawaii,there are these cold winter mornings, and you step outof a warm shower onto a cold tile floor.And you say, "That's cold."And so you immediately jump on to a rug orunto a bath mat which feels warm.Yet, if you were to take the temperature of the floorand the bath mat, you'd find them to be exactly the same temperature.So, why does the cold tile floor feel colder than the bath math,even though they're both the same temperature.Well in this case it has to do with the rate of heat lostfrom your body which is perceived by your brain as a difference in temperature.So, the point of all this is that if you're tryingto make a subjective or objective measurementof temperature, you can't rely simply on your senses.

People are very sensitive to temperature changes,and at one time what feels cold, might feel warm.I'm sure you've had the experience of suddenly walking into a roomand it feels cold, and a few minutes later, it feels warm.Your metabolism adjusts to things.So, what I want to do at this point is simply to define temperaturevery simply as a degree of hotness or coldness.This is not a very satisfactory definition, but it is a numericalanswer at least with a thermometer to the question of how hot is it?Everybody would agree that boiling water is warmer than ice,regardless of how hot or cold we think they might be.No two people would disagree on that fact.Even so, this is not a very satisfactory definition.But, like any kind of a good definite, a purelyquantitative definition begins with a measurement of some kind.Well now it's time to consider exactly how we come up with thisquantitative definition of temperature.In other words, measuring the temperature.Everybody knows how you measure the temperature, right?You measure the temperature with a thermometer.But, what is a thermometer anyway?Well, that's simple.

A thermometer is simply an instrument which usessome thermal property of matter.Of course, we don't know what a thermo propertyof matter is, but we'll get to that in a minute.A thermometer is designed so that we can measure a temperatureof something by observing some property which changes with temperature.That's what we mean by thermal property.But, we'll come back to that in a minute.One thermal property that we know of, that everybodyis aware of, I think, is that of thermal expansion.Almost all things, substances, that is, become larger when they get hot.They expand, they contract.

Now here in Hawaii we don't have to worry about this so much,but in colder climates, for example, when you build abridge, you have to consider that the bridge is going to expand afew inches from summer to winter.So you have to build in some sort of expansion mechanism.In roads, when you build roads, here in Hawaii again we don'thave much of a temperature change, but in places wherethe temperature changes from below zero in the wintertimeto a hundred degrees in the summertime, roads haveto have cracks in them, and sidewalks have to have cracksin them so that when the concrete expands, it doesn't buckle.OK, so with thermal expansion in mind as onepossible thermal property, now we can turnour attention to the principles of thermometers.

So the principles of thermometers are really very simple.It's based upon something that we all know about temperature,but we may have never rationalized or may have never thought about.That's simply that when you put two objects of differenttemperatures together, they will eventually reach a common degree of warmth.In other words, hot objects get colder, and cold objects getwarmer until the two objects come to the same temperature.We know this already.It never happens the other way, does it?Wouldn't you be surprised if you took a piece of ice outof the refrigerator and the ice got colder and the room got warmer?It simply doesn't happen that way, does it?Or if you put ice into your beverage and the beveragegets warmer and the ice gets colder.No, of course, it doesn't happen that way.So, the thermometer is based on that principle, and when you puta thermometer next to something, the thermometer gets warmerand the object gets a little bit colder, but the principleof using the thermometer is that it doesn't get very much colder,so that we don't change the temperature very much in the act of measuring it.So, one of the things you want to do for a thermometer is to usesomething which will reach an equilibrium temperaturewith the object that's being measured, but without drawingtoo much of the heat out of that object.So we can say it this way.

The thermometer measures the equilibrium temperatureof any object with which it is contact.OK.So the question then is, how do you actually measure this?This relies upon what we can call the thermal properties of matter.The thermal properties are very simple.It's a simple thing to describe.It's not always easy to understand.But the thermal property of matter is any property whichchanges in any kind of a regular way with temperature.Thermal expansion is one example.If you heat something up, its size changes and it expandsand the expansion is proportional to the temperature change.So we can use this as a thermometer.Other things that do this, the pressure of a gas, for example,as the gas gets warmer, its pressure increases.Or for that matter, if you put the gas into a container like aballoon where it can expand, its volume also increases.So, in principle you could use either pressure or volume of a gas.In practice this doesn't work very well because the pressureand volume of the gas are also sensitive to atmospheric pressure.So, if you happen to measure the temperature on a day when astorm's passing by, you'll get an inaccurate result.There are several other things.For example, the luminosity.

You've probably noticed that when you, if you have an electricstove, if you turn it on to medium, it glows with a dull red,and if you turn it on to high, it glows to bright red.Most of the time you can't see the glow on medium,but try this at home at night sometime.Turn all the lights off and turn the stove on to medium and you'llsee that it glows a really, really dull red, and as you turn thetemperature up, you find that it grows brighter and brighter and brighter.This can actually be used to measure temperature.How do you suppose, for example, that theymeasure the temperature of lava coming out of a volcano.Suppose somebody walks up there with a thermometer and sticks it in?Probably not.What they do is to look at it from a distance with ana thermometer called an optical pyrometer.Isn't that a nice name, an optical pyrometer?Which basically looks at the color of the lava or anything elseand matches it to a predetermined colorto determine the temperature.This, by the way, is the type of thermometer that you can nowbuy at Longs or other stores where you stick it in your earand it reads your temperature, your bodytemperature, almost instantaneously.

Another thermal property is electrical resistance.We don't know much about electricity as far as this coursegoes, but the electrical resistance of something changestemperature, and this can be used as a way of measuring.Digital thermometers and a temperature probe in yourmicrowave and things work like that.So all of these things are useful as temperature measurement,but what we want is something which isproportional and easily observed.Right?So some thermal property has to be something that we can seeand that we know is proportional before we can use it.So now we can see how these various thermal propertiesare used to make different kinds of thermometers.I already mentioned one type which is the luminositythermometer which measures the brightness or the color of something.And you may be aware of the fact that as things gethotter, they get brighter as well as change color.We'll pick that up a little bit later on in the program, too, when wetalk about radiation as a form of heat transfer.So, let's go look at some of these types of thermometers.I have a collection of thermometers here.The most common type is the liquid in glassthermometer which I can't get off the tabletop.There we go.And this is the type of thermometer you usually see.It's the common type that you use for an outdoorthermometer or a refrigerator thermometer.You'll notice that you don't see the liquid in here unless it turns to the right angle.This is because the liquid inside the glass is really not round.It's really a very thin ribbon.It's a thin ribbon, because in order for this to work,the expansion has to be such that it will move a fairlylarge amount with a small temperature change.

Now liquid doesn't expand much when it heats up, so that meansthat the volume of liquid inside the tube has to be a fairly smallfraction of the total volume of the liquid in the ball at the bottom.This is the liquid in glass.The typical liquid that's used in here is alcohol and water.There are limitations to this, of course, because a mixutureof alcohol and water freezes at a fairly low temperature.You notice this goes down to about to about minus 30 degrees,so below that the liquid will freeze and the thermometer can't be used.For that reason another type that's commonly used, the liquidin glass, is the mercury thermometer.This is a laboratory thermometer, and I don't think I can turn thisso you can actually see the mercury because themercury in here is a very, very thin strip.It does this because the thinner the ribbon of mercury is,the more precise and accurate the thermometer is.So this particular thermometer only goes to a very small range,actually, it goes between the freezing and boiling temperature of water.But it's fairly accurate.And again, you can see the mercury.You can't see the mercury on the ball at the end.

Another type of thermometer is the electrical thermometer.That's this one.This uses electrical resistance.This particular one is calibrated in degrees Fahrenheit.and basically this has an integrated circuit and a chipinside which reads the resistance of a piece of metal whichchanges, the thermal property changes, with the temperature.Another type is the bimetal thermometer.That's this one.This particular one uses a coil of wire rather than a straight,I should say a coil of bimetal strip, which I'll explain in a minute.And you can see here that if I heat this upin the bottom, that it just sort of spins around.If I can do this without burning my fingers.You see that it heats up, as you expect a good thermometer to do.OK.The other thing then is, we can look at a bimetal stripin linear form rather than the curved form.It looks something like this.This is a bimetal strip.It has two pieces of metal.It's hard to see exactly what it looks like,but I'll explain this on the ELMO in a minute.

What I want to do is show you how this works.Let me get my torch out here.Don't try this at home, if you have a torch.Doesn't everybody keep a torch around all the time?You know, I always keep one, just in case you need to burn something.There we go, light the torch up.So, watch what happens with the strip.As I put it into the fire, as it heats up, it bends.And you notice that it bends in the same directionregardless of which side I heated it on.In fact, whatever part of it I bend, right in frontof the heat, it bends in that direction.So, I can cool this off.I just happen to have some water here.I can cool this off by quenching it in the water, and you'll see thatit will quench in the water and as soon as it comesout of the water, it will straighten up again.OK.Notice how when the water cools it, when it comes out, it straightens up again.So, what I'd like to do now is go to the ELMOand describe to you how this bimetal strip works.

So let me turn the torch off, and let's go over to the ELMO.I hope the torch goes out pretty soon.OK, here we go.So, here's the way a bimetal strip works.It actually works on the idea of thermal expansion.And if I draw this exaggerated to scale,a bimetal strip works something like this.Two pieces of metal of different types.One piece of metal might be copper, the other piece might be zinc.So, I'll color this a different color just so we can see thatthere's two different kinds of metal.So what happens is that the two pieces of metal havedifferent thermal expansions.What that means is that for a given temperature change thetwo pieces of metal expand at different rates.So, what happens to something like this if the two piecesexpand, those that get longer, but one gets longer than the other?Well, the only thing that can happen is that it bends like this.Why does it bend?Well, it's the only way you can keep two things attachedand still keep them together, if one is longer than the other.

I think you can see from this that the length of the top red piece,the distance from here along here is longer than the distance along here.So the greater the difference in the rate of expansion,the more the thing bends, and also, the greaterthe change in temperature, the more it bends.And, of course, when you cool it off so that it comes backto room temperature again the two things come back to the same length.These are very useful, not only in the thermometer that I showedyou, which, by the way, has a bimetal strip that's coiled likethis, so that when it expands it uncoils and just simply have aneedle attached to the end of this so that as it coils and uncoils the needle moves.But the most use of this kind of thing is in thermostats.

You know what a thermostat is, don't you?Thermo means temperature, stat means stable or not changing.So a thermostat works something like this.You have a bimetal strip and you have one end of the bimetalstrip connected to an electrical circuit.And you have the other side of the electrical circuit connectedto two switches, to two wires up at the top.So, when the temperature gets warm, the bimetal strip bendsand when it gets to a certain temperature it bends hereand turns off a switch which in turn, turns off the heater.OK.And as the room cools down then, the bimetal strip comes back to here.And if it gets too cold, it will bend this way and eventually itwill contact this switch and turn the heater back on.So you can adjust the thermostat by several different ways.Either by changing the distance between these polesor by various other ways, usually the bimetal strip is actually of this type.But, not only can you run a heater this way, but you can run an air conditioner.For example, when the room gets too hot over here, you can havethis switch run an air conditioner.And when it gets too cold over here, you can have it turnon the heater so you can keep the temperaturewithin the range of these two bimetal strips.Very convenient, very ingenious device, if you think about it.

It's time now to look at different ways of measuring temperaturein the form of different temperature scales.But before we do that I have to clean up my mess here a little bit.Let me get rid of some of this stuff.You know it gets so messy when you do all this kind of stuff.Let's see, I don't want to break that one so, it goesthere...and I'll clean up this stuff.I just...get a little water here.There!Now we're ready.Temperature scales.

The first measurement of temperature,the quantitative measurement was made in 1708.This was by Olan Roemer.You may remember his name, if you've been paying attention.He's also the first person to make the first accurate measurementof the speed of light, back in 1675.Roemer's idea comes into play here because he gave the ideaabout how to do this to a man named Fahrenheit.You've probably heard that name before.Unfortunately, Fahrenheit got this concept, but he missed the details.The idea is that in order to make any kindof a temperature scale, it requires two "fixed" points.The two "fixed" points determine the scale in the same way thattwo points determine a line in geometry.Several things can be used.The most common is to use the ice point and the steam point.This is a particular way that you can set this up.So here you have a mixture of pure ice and distilled water.It's pure ice because if there is impurities in the ice,or impurities in the distilled water, then it freezesand melts at a different temperature.So, this is what we call the ice point.To mark the steam point you would put the thermometer inside aclosed container above the boiling water, so that you're measuringthe temperature of the steam as it comes off.So here you have boiling water.The instrument is called a boiler.There's steam in the empty space, and, of course, you have to allowthe steam to escape so that it doesn't blow up,and then the steam point can be marked.

I'll come back and show you more specifically whathappens with this in a couple of minutes.So, what we want to look at is the Fahrenheit scale now.The Fahrenheit temperature scale was done by a man namedFahrenheit who used two different things for his "fixed" points.Instead of using a mixture of ice and water for one pointand a mixture of, the steam point for another, he used the coldestmixture he could make in the laboratory, and that wasa mixture of ice and ammonium chloride.Now, some of you probably don't know this because we don'thave snow on the roads here in Hawaii, but do you knowthat when they want to melt the show and ice off a road they put salt on the road.Does anybody know why you do this?It might be a good topic for research if you wantto write about this a little bit.The reason they do it is that a mixture of salt and ice meltsat a lower temperature than simply pure ice.So, Roemer, Fahrenheit, I'm sorry, found the coldestmixture he could attain in the laboratory which wasa mixture of ammonium chloride and ice.By the way, those of you who've ever made ice cream with anice cream maker, you know that around the bucket of ice cream you put salt and ice.That's because it keeps it at a constant temperature which islower than the normal point of ice.What Fahrenheit did was to use this as the coldestpoint which he called zero degrees.And he used his body temperature for the other point.

Now there are several different stories here.One was that his body temperature was a little high that day,and he had a fever, but he called this 100 degrees.Another story says that he used an inaccurate thermometer.That he didn't mark the point very well, and so he was off by a little bit.And yet a third story says that after it was realized what thenormal body temperature was, that the scale was changed.I don't know which one of these is actually true, but he did use theammonium chloride mixture for the low pointand the body temperature for the high point.On this scale, the ice point, the melting temperature of pure iceis 32 degrees and the boiling temperature of water turns out to be 212 degrees.It's pretty obvious, I think, that this is kind of an awkward scale.One of the reasons, by the way, that Fahrenheit did this isbecause he was concerned that in Germany in the wintertimethe temperature drops below the freezing temperature of ice,and, the ice point that he wanted there to be not negative numbers.

People don't like negative numbers.So, he didn't like below zero.It turns out, of course, that it works that it does getbelow zero, anyway, so, anyway, the point didn't work very well.Because of this awkwardness of the number of degreesbetween 32 and 212, which if you're good in arithmetic,180 degrees on the Fahrenheit scale between the freezingand the boiling of water, the Celsius scale is often used in science instead.The Celsius scale is actually based upon the ice point and the steam point.The way this works is very simple.You stick the thermometer into the ice water and you simplymake a mark on the thermometer where it comes to.Then you take the same thermometer and you stick itinto the steam and you mark that point, and you simply call thelow point zero degrees and you call the high point 100 degrees.And, of course, to make the rest of the scale you simply mark offthe scale into 100 equal marks, 100 degrees.A degree here simply means a size of a mark.We used to call this the centigrade scale.But now we call it the Celsius scale in honor of Celsius.There is one interesting point here.That when Celsius first did this, he marked this point, the steampoint, zero, and marked the ice point, 100.Nobody knows exactly why he did this.But he was corrected, and it's kind of interestingbecause what difference does it make really?I mean we're so used to thinking about a large number being hotand a low number being cold, but it really doesn't make any difference.Except that it's coincidentally as we'll see in a later program thefact that we consider that heat is the presence of somethingand coldness is the absence of something.So, we say that when something has a highertemperature it has more heat.So, using a large number to represent a higher temperatureactually turns out to be a better way to do it.

The Celsius scale is also used in a slightly different waywith the Kelvin scale or the absolute scale.We'll consider this in more detail as we move along through ourconcepts of heat and temperature, but the Kelvin scale is basicallya temperature that's based upon absolute zero.Where the zero on the Kelvin scale represents the coldesttemperature that anything can get.I don't want to get into how that's arrived at now.But rather than having an ice point, it's absolute zero,absolutely as cold as you can get.The size of the degree in the Kelvin temperature scale isthe same size as the Celsius degree in such a way thatabsolute zero is minus 273 on the Celsius scale which means,of course, that zero in the Celsius scale is plus 273 Kelvins.So, don't get confused by this, but keep it in the back of your mindand we'll come back to this later on when we get into absolutetemperature and entropy and thermal dynamics and the gaslaws and all that kind of fun stuff.OK.Although the Celsius and the Kelvin scales are easyto compare, the Fahrenheit and Celsius scales are not easy to compare.So, let's go look at the comparison between these two scales.

I want to show you this, not because you need necessarilyto be able to do the conversions, but you probably seen before theconversion between Fahrenheit and Celsius.It's 9/5 C plus 32.What I want to do is to integrate this with our conceptof the graph and the slope of a line and that sort of thing,so we can see where this comes from.What I've got here on the graph is Fahrenheit temperatureon the vertical axis versus Celsius temperature on the horizontal axis.And what I've done is to put the steam point on both axes here.So this is 212 degrees Fahrenheit, it's 100 degrees Celsius.And at the same time put the ice point which is 32 degreesFahrenheit and zero degrees Celsius.When you draw a line that connects the two of themthe line represents a conversion factor.So, if I wanted to use the line, for example, to find out what 100degrees Fahrenheit equals on the Celsius scale, I could come overhere to the graph and go down here and find that it's equal to about38 degrees or 39 degrees, or something to that effect.But that's not the point.

The point is to look at this graph.You will notice, by the way, I put one extra point on here.This is the point where the two temperatures are the same.So if you're talking about minus 40, it's both Fahrenheitand Celsius, and there's no conversion factor at all.And if you want to try a little mathematical exercise,try putting "C" equals minus 40 in this equation and see if "F"doesn't also come out to be minus 40.But this is the neat thing.When we look the this is a mathematical entity,the graph, we can see this line has a slope.The slope is the vertical divided by the horizontal, the rise over the run.You may remember this from a previous lesson.The slope then we can evaluate to be the rise of 180 degreesbecause on the Fahrenheit scale there's 180 degrees,between freezing and boiling, 212 minus 32.On the Celsius scale, there is 100 degrees between freezing and boiling.That represents the run or the horizontal part of the slope.So, the slope or the line is 180 divided by 100 whichis 9/5, and that 9/5 appears down here.The vertical intercept of this line, this is the placewhere the line intercepts the vertical axis.Notice that even though I've drawn the graph axis overhere, the zero point on this graph is here.This is zero degree Celsius.This is zero degree Fahrenheit, so that originof the graph, mathematically speaking is here,and you'll notice that the line crosses that axis at 32 degrees.So what does all this mean?Well, the slope is 9/5, the vertical intercept is 32.

In general the equation of a line is that the vertical axis is equalto the slope times the horizontal axis plus the intercept.So we can see here that the equation of the line actuallygives you the conversion between Fahrenheit and Celsius.You can also work backward from this, by the way, to find theconversion between Celsius and Fahrenheit.But let's be honest, folks, the United Statesis the only country that uses Fahrenheit, so whoeverhas to convert from Celsius to Fahrenheit?One thing that might not be clear, although if we thinkabout it, it becomes clearer, that temperature and heatare related but very distinct concepts.We can think of it this way.Adding or removing heat causes a change in temperature.If you add heat to something, it's temperature increases.If you take heat away from something, it's temperature decreases.In fact, this is true as long as no change of state is involved.For example, there's no melting takes place or no freezing takes place.We can also think of it in terms of measuring temperature wherewe said before that if you put a hot thing and a cold thingtogether the hot thing gets cooler and the cold thing gets hotter.So, at this point we can simply say that what happens is thatheat flows from the hot object to the cold object.

We haven't defined what heat is, yet.But I think we can see that, for example, temperature changeis proportional to the amount of mass for a given substance.Here we see two containers of water.And it's pretty obvious, I think, that if the two hotplates are identical, that if you have twice as muchwater in one beaker than in the other, that thetemperature change is going to be twice as greatin the same amount of time, assuming the two hot plates are equal.Notice it's the concept of temperature change.The one kilogram of water goes from 10 degreesCelsius to 70 degrees Celsius.The total temperature change is 60 degrees, 70 minus 10.The two kilograms of water in the same amount of time undergoesa similar temperature change, but it goes only, changes only 30degrees, from 10 degrees Celsius to 40 degrees Celsius.So, one kilogram of water changes its temperature by 60 degrees,two kilograms of water changes the temperature by 30 degreeswith the same amount of heat added.

I think you can also see that a large stovetop burner or aburner on high, for example, will heat the same amountof water faster than one on low.You can also see, I think, that we can say that fivekilograms of water has five times the capacityto absorb heat as one kilogram of water does.And here's one final way to think of this.A tub of water can melt more ice than a glassof water at the same temperature.Now it's time to consider what we often call specific heat.Specific heat refers to the term that it's specific bothfor a material and for a particular amount of a material.Basically what we're talking about is something that mightbetter be described as thermal capacity,or more specifically, thermal capacity per unit mass.Basically the specific heat of a substance is the amountof heat required to change the temperature of one kilogramof a substance by one degree Celsius.

You may often hear this also stated as the amount of heatrequired to change the temperature of one gram.But since the kilogram is the standard unit, we generally say it that way.Let me say it again.Specific heat is the amount of heat required to change thetemperature of one kilogram of material by one degree Celsius.So, keep in mind, now, the changes in temperatureinvolve heat transfer from hot to cold.And what this really does, the concept of specific heat,is to create a quantitative relationship between heat and temperature.Quantitative relationship.

Now keep in mind the difference betweenqualitative and quantitative,When we just say that heat, a loss of heat, causes a lossin temperature, that's a qualitative relationship.So now we want to be able to say how much heat causes how muchof a change of temperature, but in a specific substance.This is the first time anywhere in the course that we've seen theproperties of a particular substance coming into play.Keep in mind that Galileo and Newton and all these otherthings, conservation and momentum, conservationof energy said nothing at all about one substance being different from another.In fact, in those considerations all things were exactly the sameunder the freefall, under the expect of forces and so forth.So, we're beginning now to see that we do haveto consider the nature of a particular substance.

So, what we can see is that each substance actuallyhas a different specific heat capacity.In fact, a substance like alcohol will change its temperaturemuch less than an equal substance, an equal amount of a substance, like water.I think we have a graphic.Let's see what we can see here.Here we see a similar picture to what we saw before, but thistime we have one kilogram of water on one hot plateand we have one kilogram of ethyl alcohol on another hot plate.And what we see is that, once again, we're assuming that thehot plates have a constant output of heat, and we're lookingat the change in temperature over a given time period.So we start off with one kilogram of water at 10 degrees Celsius,one kilogram of ethyl alcohol also at 10 degrees Celsius.And after a certain amount of time is past,we see that the water has gained 30 degrees,Celsius degrees, while the alcohol has gained 52 degrees.So, for an equal amount of material, one kilogram,the alcohol has almost doubled the amountof temperature change of the water.So what we're seeing here is a different thermal capacity.In other words, it's a different capacityto absorb heat without changing its temperature.We can think of this another way.That if you have a piece of hot iron, for example, and put thisinto water, the iron will lose more temperaturethan the water gains per unit mass.In other words one kilogram of iron put into one kilogramof water, the iron will lose more temperature than the watergains, even though the amount of heat that it loses will beexactly the same as the water gains.

Now, if this is a little confusing, it's OK.I sort of want you to think about this and we'll come back to thisin the next program when we try to understand specific heatand temperature and that sort of things in slightly different terms.So, for now we can note that for water, which is a fairlystandard substance, the specific heat is onekilocalorie per kilogram per degree Celsius.In fact, this defines the concept of a Calorie.One kilocalorie per kilogram per Celsius degree.That means that if water changes its temperature by one degreeCelsius, it takes one kilocalorie of heat to do that.Now, we use the word, kilocalorie, here.When you talk about food and kilocalories and Calories,like if you go eat a Mcdonald's hamburger it's about like 4000 Calories.No, I'm sorry, it's about 1500 Calories.Those Calories are kilocalories.So what we're saying here is that there's enough energy containedin a Mcdonald's hamburger to raise the temperature of 1500kilograms of water by one degree Celsius.That sort of gives you the idea that we, as people, are veryinefficient users of energy, if we had to use that much energy.OK, we also can see that one reason why we use wateras a standard is simply because water is a very commonsubstance and it's easily purified as opposed to other substances.The interesting this is that water has the highestspecific heat of all common materials.

There's only one known substance that has a higher specific heatthan water, and that is liquid ammonia, and I don't meanthe kind of ammonia you buy at the store.I mean pure liquid ammonia.The stuff you buy at the store is ammonia dissolved in water.So, if we look at the specific heats of some of thesesubstances, we can see how much higher water is than all of them.It's not just a little bit higher, it's quite a bit higher.Aluminum, for example, has a specific heat of almost athousand, 901 joules per kilogram per degree Celsius.Oh, I've done a unit switching thing on you here.Well, that's OK.We're going to come back in the next program and lookat the relationship between joules, which is a unitof mechanical energy and Calories which is a unit of heat energy,so this is a way of getting you to see how these two things are related.But, look at this, aluminum has 901 joules per kilogram perdegree Celsius; where water 4190.In other words, almost five times the specific heat of aluminum.Even a substance like iron which we normally think of as being,as retaining heat very well, has a relatively low specific heat.

Now if you look at iron versus aluminum, you see thataluminum has a specific heat almost twice as great as iron.Now if you've ever cooked with an aluminum skillet, you might say,"Well, you know the aluminum skillet loses heat a lot faster than the iron."Part of the reason for this apparent discrepancy is the factthat iron is much more dense than aluminum, so one kilogramof iron takes up a lot smaller space.Another way to say this is an aluminum skillet and an ironskillet are the same size, the aluminum skillet weighs onlyabout half as much, so that the effect of the specific heat is really lost.You also notice here that of the other substances listed, ice,which is actually another form of water,has a different specific heat than liquid water.It's only about half that of liquid water.And steam, which is another form of water, has a specific heatabout the same of ice, but still only about half that of water.So, in the next program we'll consider why it is that iceand steam and water behave as different substances when westudy the concept of specific heat in a little more detail.

Now it's time to consider a change of state.Silico: "Why are we moving to another state, I like it here in "how vhy hee."Not that kind of change of state, I mean the change of a physical state.Well, wait a minute.That doesn't help either.Let's just go to the graphic and see what we mean by this.What we mean by physical state is a phase of matter or a state of matter.In other words, solid, liquid or gas.I think everybody understands this.That water has three separate phases although we don'tusually see the gaseous state of water because it's invisible.But we certainly know this transition from solid to liquid.In one direction it's called melting, the other direction it's called fusion.On the other hand, you can go from liquid to a gas, but the process is called evaporation.You can go from a gas back to a liquid.This process is called condensation.Less well known is the transition from a solidstate to the gaseous state directly.This is called sublimation, whether it goes frontwards or backwards.I think you probably are aware of this kind of change.I'm sure everybody's seen dry ice before.Why do you call it dry ice?Because it has no liquid state.What happens is that it goes directly from the solid to the gaseous state.

Now these kinds of changes occur at certain temperaturefor a given pressure for different substances.We can look, for example, at carbon dioxide.And we can see how this works.Now every substance would have a similar relationship.What we see here is a line which separates the solid statefrom the vapor state and in the middle we have a liquid state.A point where these three lines join is called the triple point.If we look at typical conditions for carbon dioxide here on earth,we see that one atmosphere of pressure, that's standardatmospheric pressure, and typical temperatures,that the gaseous state simply doesn't exist.For example, here at one atmosphere we look and yousee that the carbon dioxide goes from a solid state directlyinto the vapor state without ever passing through the liquid state.In fact, to get a liquid carbon dioxide you haveto have pressures up above 10 atmospheres.Ten atmospheres isn't very much pressure.A similar thing exists for all substances.Water has a triple point somewhere near its freezingtemperature at very low pressures.The reason we consider these changes of stateis because changes of state involve heat.This type of heat is called latent heat.

The word latent simply means hidden.It's hidden because it's not used for a change in temperature.That's kind of hard to understand, but basically we can look at it this way.When something goes from a solid to a liquid, heat is absorbed.When something goes from a liquid to a gas, heat is absorbed.We all know this.When you get out of the water at the beachand the wind's blowing, you feel cold.What's happening is water is evaporating from your skinturning into a gas, and requires heat to do so, and the heatcomes from the only place around, which draws the heat from your body.But when I say that temperature change is notinvolved, I mean something a little bit different.And I think to see what I mean by that we have to go to the ELMO.

Let's get an imaginary situation here.It's imaginary for our purposes but can actually done.And what we want to do is to put a piece of ice, a block of ice, inside a container.And we're going to seal off the container with an escape valveon it so that we can turn this into steam a little later on.OK, so we're putting this inside the container.And let's start the ice at already frozenwith a thermometerinto it.And to indicate this I'm just going to do this and stick a little,a "T" over here to indicate that we're measuring the temperature of the ice.And let's start the ice off at minus 10 degrees Celsius.In other words about 10 degrees below its melting temperature.Let's look at a graph of what the temperature looks likeinside this container as time passes.So, here we're going to start the ice off at minus 10 degrees Celsius.

Now what we want to do is to add heat to the container,and we can do this in a slow enough way so that the icecomes to the same temperature throughout.So the ice is going to warm up and be approximately the sametemperature all the way through.So, here's what we would see happening.As soon as we start heating, we'd find that the temperature beginsto increase and the ice warms up.

Now I know it's hard to think of ice as warming up, but there'ssome ice that is colder than others.But at zero degrees Celsius, something interesting begins to happen.You know what happens there, of course, right?Water begins to appear as the ice melts.So, the ice transforms itself into water,but what happens after that is very strange indeed.What happens is that as long as there's both ice and waterpresent in the container, the temperature does not change.In other words, the temperature of the ice now is at zero degreeCelsius, and as time passes, the temperature of the ice remainsconstant at zero degrees Celsius, as does the water.In fact, what we would find is that we have a mixture of iceand water both at zero degrees Celsius.In fact, you can think of it this way.The ice can get no warmer than zero degrees Celsius,and the water can get no colder than zero degrees Celsius.So, as long as both of them are present, no heat can beexchanged between them because their temperatures are fixed.So, the temperature remains constant until the time whenthe last bit of ice disappears at which time the water nowbegins to heat, but the water heats at a slower rate.Because it has a higher specific heat than the ice.And you can see in a general way here.If we're looking at temperature versus heat, that the slopeof this line actually represents the specific heat of the ice.

The relationship between heat and temperature.The faster something heats up, the lower its specific heat.So, here we see that the ice, the slope of this line, is less thanthe slope of this line, so that in a given amount of time, the waterchanges temperature by a lesser amount.This would continue on the same scale here.This line would be broken, but this would continue until thetemperature reaches 100 degrees Celsius,at which point the water begins to boil.At 100 degrees Celsius as the water begins to boil,something else strange happens now.The water can get no hotter than 100 degrees Celsius while it's boiling.So the temperature will stay constant until the water boilsaway, at which point, when the last drop of water disappears,then the temperature of the steam inside now begins to increasein temperature again, but at a different rate from the water.In fact, we saw before that the specific heat of steamis about the same as that of water.So, you probably know this.Maybe you don't.That turning up the heat on boiling water doesn't increase its temperature.All it does is make it boil away faster.It makes the bubbles appear faster, but doesn't really help.It doesn't really increase the boiling rater.

We can now look at a general principle here.We see that there are certain points here where things happen.These points represent the change of state, and, in fact, at thistime there's only ice present in the container.I'm going to zoom in on this is a little bit, just so wecan see the writing a little bit better.At this point, during this time, there's ice and water present,and as long as both phases or both states are present,no temperature change takes place.The heat that's involved here is latent heat.In other words, this amount of heat.Notice here that heat is absorbed by the ice as it melts withouta corresponding change in temperature.For water this amounts to about 80 kilocalories per kilogram.You notice that 80 kilocalories per kilogram is almost as much heatas it takes to raise the water from its freezing point to its melting point.This is 100 degrees, so this distance represents only 100kilocalories per kilogram because the specific heat of water isone kilocalorie per kilogram, so you have 100 degrees, so 100 kilocalories.During this state, of course, liquid water is the only phase present.And once the water starts to boil, you have during thisstate, now both water and steam.And, of course, some of the steam is present in bubbles, and someof it escapes, but we have a closed container up here.Once the water starts to boil, we now have water and steam.

You notice that whenever there are two phases present at the sametime, or states present at the same time, then no furthertemperature change occurs until both phases are missing.So, it turns out that this number is huge.In other words, the latent heat of evaporationof water is about 540 kilocalories per kilogram.This is a tremendous amount of heat that it takes to evaporate water.And I want to point out at this time that this tremendousamount of heat necessary to evaporate water stays with the water vapor.So that when the water recondenses someplace else, it gives back that heat.If you've ever been burned by steam, you probably recognizethat it's much worse to be burned by steam than by water.On the other hand, we can look at this on a largerphysical scale and recognize that this latent heatof condensation being given back is the power behind a hurricane.The water evaporates from the surface, absorbs a tremendousamount of heat, and as it condenses in the upperatmosphere, it gives off that heat which causes the air to risemore, which causes more water to condense, which causes moreheat, which causes more rising,which causes more cooling,which causes more condensationand so simply you have a verypowerful engine driven by this latent heat of water.We have said that heat will flow from hot objects to cold objectsuntil an equilibrium temperature is reached.But we said nothing about how the heat does this.

Now the textbooks cover this material fairly well so I'm onlygoing to review it very briefly for you and encourage you to goto the textbook and actually look at the pictures and look at theways in which this heat transfer takes place.The idea here is that the temperature of something willremain constant as long as there's no net gain or loss of heat.It's when heat flows into something or flows outof something that its temperature changes.Now in reality, in the real world, time, at any given time, heat isalways flowing into and out of something.For example, I'm radiating heat away at the moment.The effectiveness of the various methods of heat transferdepends upon the materials, the situation, the differencein temperature, and other very complicated things that we don't want to get into.I might mention, by the way, that our friend, Isaac Newton, wasone of the first people to consider the concept of heat transfer.And, in fact, Newton came up with what he called,the law of cooling, which is still our basic wayof understanding this process of heat transfer today.So, there are actually three sensible processes and one unsensible process.I love the word, sensible, there.The unsensible process is latent heat.It's unsensible because you don't sense it.You don't notice the heat in a latent heat process.The sensible processes are of three types.There's convection, conduction and radiation.Now, keep in mind, that in reality all of theseprocesses take place all at once.Latent heat doesn't take place, of course, unless there is changeof state involved, but all of the other processes take place all the time.

Convection is simply a movement of a warm fluid to a colder place.If you heat water from the bottom, the water expands and risesleaving a empty space in the bottom, so cold water comesto fill it and eventually sets up a cycle, a convection cycle,where hot water is heated at the bottom, rises to the top,replaced by cold water which rises to the top, and so forth.The convection I have to point out is onlyapplicable in fluids which includes liquids and gases.The second type of heat transfer that we're familiar with, thesensible heat transfer, is conduction.Everybody knows what conduction is.I'm sure at sometime in your life you must have stuck a forkinto the hibachi when you're cooking and find that the endof the fork gets hot even though its not near the fire.Or you've put a spoon into a cup of coffee and find thatthe spoon gets hot on the end.The conduction is transferred, is a transferof heat through the substance by atomic collisions.Oh, I used that word, atomic.Well, we'll come back and learn about atomiccollisions a little bit later on.

The third type of heat transfer is radiation.Radiation is a type of electromagnetic interferenceswhich is emitted from all objects above absolute zero.The book goes into some detail about this.And all I want to note is here is something I, to come backto something I already talked about a little while ago in this program.Which is that the hotter an object becomes, the more radiation it gives off.And also, the hotter an object becomes,the different color of radiation it gives off.This is important and useful because, for example,we can look at the spectrum of the sun and figure outwhat the surface temperature of the sun is.In the same way that we can look at the surface of a lava flowand figure out what the surface, what the lava temperature is.We can use this for many different applications.For example, we've discovered that there are differentcategories of stars based upon their color and their surface temperature.There are blue stars and red stars as we mentioned in an earlier program.I want to conclude this program todaywith a little foray into the biological area.Not that we're really going to study biology.You have to take biology course to do that,but I do want to consider the impact of heat on life.

Heat is produced by combustion of food in body tissues.This is very much like combustion of fire.It's just that it's slowed down a bit and regulated by enzymes.And again, if you want to study enzymes, you need to go take a biology course.The idea is temperature control.The rate of energy usage is controlled somehow by thesebiological processes, and most organisms, ourselves included,rely upon environmental factors for temperature control.And most organisms, including ourselves, have very littletolerances for temperature changes.As you're probably aware most of us here in Hawaii, anyway,put on a sweater if it drops below 75 degrees, and we complainabout the heat, if it goes much over 85.So we have a very low tolerance for temperature.The aquatic life, for example, relies upon the heat of the water.And these animals being cold blooded actually slow down in the winter.And many animals, fish, for example, in ponds that freezein the wintertime, go to the bottom where the water doesn't freeze.The important point here is that the body heat in mammals whichbuilds up due to the combustion of food has to be dissipated,otherwise, the body temperature would increase.How is it dissipated?Well, of course, it's dissipated by the methods of heat transfer.On one hand there's conduction.

We conduct heat directly to the air.On the other hand, it's convection.We know we get colder when the wind blows.On the other hand, there's radiation.We radiate heat away.You can feel this sometimes when you're very hot, if you hold yourhand up to your face, you can feel the heat coming off your face.Latent heat plays a role as well, more so than the others.In fact, latent heat is a very effective method of heat transfer.Perspiration evaporates and cools us off.Other mammals, like dogs, (oha, oha, oha) they pant,lose heat from their tongue.Cats lick themselves, the water evaporates.So, all of these are very important methods in heat transferand heat control in organisms of all types.Here we are at the end of another program.Time for the summary and conclusions.

In this program we've sort of taken a different tack.We've started now to look at different substances.We've seen a definition of temperature,how to measure temperature; different temperature scales.In fact, this program really serves as an introduction or atransition, if you like, into the concept of matter, which willbe the subject of the next two programs.The most important thing we've talked about today, I think,is the concept of specific heat and latent heat.Because we need to answer the question eventually,"Why does matter behave this way?"Why do things have different specific heats and why dothings have different latent heats?The other things, the difference between heat and temperaturewe'll come back to in a later lesson when we getinto the idea of atoms and molecules and all that sort of thing.So, we'll come back to that later on.As far as the heat and life goes, you might want to read in thetextbook about this, but this is kind of an important thing.And when you go to a biology class later on, you can take this with you.Well, I don't really have that much more to say about this program.So remember, when it comes to science, get physical.Silico: "Is it cold in here?Or is it just me?"Of course, you're cold.You're cold hardware, you're silicon.What did you expect?The only time you ever get warm is when electricity flowsthrough you, and you probably get heated up....Music