So, under slow compression, a gas will increase in temperature, and under slow expansion it will decrease in temperature. We now return to our drop of water and look in another direction. Suppose that we decrease the temperature of our drop of water.
Suppose that the jiggling of the molecules of the atoms in the water is steadily decreasing. We know that there are forces of attraction between the atoms, so that after a while they will not be able to jiggle so well.
What will happen at very low temperatures is indicated in Fig. This particular schematic diagram of ice is wrong because it is in two dimensions, but it is right qualitatively. The interesting point is that the material has a definite place for every atom, and you can easily appreciate that if somehow or other we were to hold all the atoms at one end of the drop in a certain arrangement, each atom in a certain place, then because of the structure of interconnections, which is rigid, the other end miles away at our magnified scale will have a definite location.
So if we hold a needle of ice at one end, the other end resists our pushing it aside, unlike the case of water, in which the structure is broken down because of the increased jiggling so that the atoms all move around in different ways. The difference between solids and liquids is, then, that in a solid the atoms are arranged in some kind of an array, called a crystalline array, and they do not have a random position at long distances; the position of the atoms on one side of the crystal is determined by that of other atoms millions of atoms away on the other side of the crystal.
Figure is an invented arrangement for ice, and although it contains many of the correct features of ice, it is not the true arrangement. One of the correct features is that there is a part of the symmetry that is hexagonal. So there is a symmetry in the ice which accounts for the six-sided appearance of snowflakes.
Another thing we can see from Fig. When the organization breaks down, these holes can be occupied by molecules. Most simple substances, with the exception of water and type metal, expand upon melting, because the atoms are closely packed in the solid crystal and upon melting need more room to jiggle around, but an open structure collapses, as in the case of water. If we wish, we can change the amount of heat.
What is the heat in the case of ice? The atoms are not standing still. They are jiggling and vibrating. We call this melting. As we decrease the temperature, the vibration decreases and decreases until, at absolute zero, there is a minimum amount of vibration that the atoms can have, but not zero.
This minimum amount of motion that atoms can have is not enough to melt a substance, with one exception: helium. Helium merely decreases the atomic motions as much as it can, but even at absolute zero there is still enough motion to keep it from freezing. Helium, even at absolute zero, does not freeze, unless the pressure is made so great as to make the atoms squash together. If we increase the pressure, we can make it solidify. Atomic processes So much for the description of solids, liquids, and gases from the atomic point of view.
However, the atomic hypothesis also describes processes, and so we shall now look at a number of processes from an atomic standpoint.
The first process that we shall look at is associated with the surface of the water. What happens at the surface of the water? We shall now make the picture more complicated— and more realistic—by imagining that the surface is in air.
Figure shows the surface of water in air. We see the water molecules as before, forming a body of liquid water, but now we also see the surface of the water. Above the surface we find a number of things: First of all there are water molecules, as in steam. This is water vapor, which is always found above liquid water. There is an equilibrium between the steam vapor and the water which will be described later.
In addition we find some other molecules—here two oxygen atoms stuck together by themselves, forming an oxygen molecule, there two nitrogen atoms also stuck together to make a nitrogen molecule. Air consists almost entirely of nitrogen, oxygen, some water vapor, and lesser amounts of carbon dioxide, argon, and other things. So above the water surface is the air, a gas, containing some water vapor. Now what is happening in this picture?
The molecules in the water are always jiggling around. From time to time, one on the surface happens to be hit a little harder than usual, and gets knocked away.
It is hard to see that happening in the picture because it is a still picture. But we can imagine that one molecule near the surface has just been hit and is flying out, or perhaps another one has been hit and is flying out. Thus, molecule by molecule, the water disappears—it evaporates. But if we close the vessel above, after a while we shall find a large number of molecules of water amongst the air molecules.
From time to time, one of these vapor molecules comes flying down to the water and gets stuck again. So we see that what looks like a dead, uninteresting thing—a glass of water with a cover, that has been sitting there for perhaps twenty years—really contains a dynamic and interesting phenomenon which is going on all the time.
To our eyes, our crude eyes, nothing is changing, but if we could see it a billion times magnified, we would see that from its own point of view it is always changing: molecules are leaving the surface, molecules are coming back. Figure Why do we see no change? Because just as many molecules are leaving as are coming back! Therefore there are more going out than coming in, and the water evaporates. Hence, if you wish to evaporate water turn on the fan!
Here is something else: Which molecules leave? When a molecule leaves it is due to an accidental, extra accumulation of a little bit more than ordinary energy, which it needs if it is to break away from the attractions of its neighbors.
Therefore, since those that leave have more energy than the average, the ones that are left have less average motion than they had before.
So the liquid gradually cools if it evaporates. Of course, when a molecule of vapor comes from the air to the water below there is a sudden great attraction as the molecule approaches the surface. This speeds up the incoming molecule and results in generation of heat. So when they leave they take away heat; when they come back they generate heat. Of course when there is no net evaporation the result is nothing—the water is not changing temperature. If we blow on the water so as to maintain a continuous preponderance in the number evaporating, then the water is cooled.
Hence, blow on soup to cool it! Of course you should realize that the processes just described are more complicated than we have indicated. Thus the air dissolves in the water; oxygen and nitrogen molecules will work their way into the water and the water will contain air. If we suddenly take the air away from the vessel, then the air molecules will leave more rapidly than they come in, and in doing so will make bubbles. This is very bad for divers, as you may know.
Now we go on to another process. In Fig. If we put a crystal of salt in the water, what will happen? Strictly speaking, the crystal is not made of atoms, but of what we call ions. An ion is an atom which either has a few extra electrons or has lost a few electrons. In a salt crystal we find chlorine ions chlorine atoms with an extra electron and sodium ions sodium atoms with one electron missing. The ions all stick together by electrical attraction in the solid salt, but when we put them in the water we find, because of the attractions of the negative oxygen and positive hydrogen for the ions, that some of the ions jiggle loose.
Notice, for example, that the hydrogen ends of the water molecules are more likely to be near the chlorine ion, while near the sodium ion we are more likely to find the oxygen end, because the sodium is positive and the oxygen end of the water is negative, and they attract electrically.
Can we tell from this picture whether the salt is dissolving in water or crystallizing out of water? Of course we cannot tell, because while some of the atoms are leaving the crystal other atoms are rejoining it. The process is a dynamic one, just as in the case of evaporation, and it depends on whether there is more or less salt in the water than the amount needed for equilibrium. By equilibrium we mean that situation in which the rate at which atoms are leaving just matches the rate at which they are coming back.
If there is almost no salt in the water, more atoms leave than return, and the salt dissolves. Figure Figure In passing, we mention that the concept of a molecule of a substance is only approximate and exists only for a certain class of substances.
It is clear in the case of water that the three atoms are actually stuck together. It is not so clear in the case of sodium chloride in the solid. There is just an arrangement of sodium and chlorine ions in a cubic pattern. It turns out to be very difficult, in general, to predict which way it is going to go, whether more or less of the solid will dissolve. Most substances dissolve more, but some substances dissolve less, as the temperature increases.
Chemical reactions In all of the processes which have been described so far, the atoms and the ions have not changed partners, but of course there are circumstances in which the atoms do change combinations, forming new molecules. This is illustrated in Fig. A process in which the rearrangement of the atomic partners occurs is what we call a chemical reaction. The other processes so far described are called physical processes, but there is no sharp distinction between the two.
Nature does not care what we call it, she just keeps on doing it. This figure is supposed to represent carbon burning in oxygen. In the case of oxygen, two oxygen atoms stick together very strongly. Why do not three or even four stick together? That is one of the very peculiar characteristics of such atomic processes. Atoms are very special: they like certain particular partners, certain particular directions, and so on.
It is the job of physics to analyze why each one wants what it wants. At any rate, two oxygen atoms form, saturated and happy, a molecule. Figure The carbon atoms are supposed to be in a solid crystal which could be graphite or diamond1. It is given the chemical name CO. But carbon attracts oxygen much more than oxygen attracts oxygen or carbon attracts carbon.
Therefore in this process the oxygen may arrive with only a little energy, but the oxygen and carbon will snap together with a tremendous vengeance and commotion, and everything near them will pick up the energy. A large amount of motion energy, kinetic energy, is thus generated. This of course is burning; we are getting heat from the combination of oxygen and carbon. The heat is ordinarily in the form of the molecular motion of the hot gas, but in certain circumstances it can be so enormous that it generates light.
That is how one gets flames. In addition, the carbon monoxide is not quite satisfied. One oxygen atom could attach itself to the CO and ultimately form a molecule, composed of one carbon and two oxygens, which is designated CO2 and called carbon dioxide.
If we burn the carbon with very little oxygen in a very rapid reaction for example, in an automobile engine, where the explosion is so fast that there is not time for it to make carbon dioxide a considerable amount of carbon monoxide is formed.
In many such rearrangements, a very large amount of energy is released, forming explosions, flames, etc. Chemists have studied these arrangements of the atoms, and found that every substance is some type of arrangement of atoms. To illustrate this idea, let us consider another example. It is some kind of molecule, or arrangement of atoms, that has worked its way into our noses.
First of all, how did it work its way in? That is rather easy. If the smell is some kind of molecule in the air, jiggling around and being knocked every which way, it might have accidentally worked its way into the nose. Certainly it has no particular desire to get into our nose.
It is merely one helpless part of a jostling crowd of molecules, and in its aimless wanderings this particular chunk of matter happens to find itself in the nose. Now chemists can take special molecules like the odor of violets, and analyze them and tell us the exact arrangement of the atoms in space.
We know that the carbon dioxide molecule is straight and symmetrical: O—C—O. That can be determined easily, too, by physical methods. However, even for the vastly more complicated arrangements of atoms that there are in chemistry, one can, by a long, remarkable process of detective work, find the arrangements of the atoms.
Figure is a picture of the air in the neighborhood of a violet; again we find nitrogen and oxygen in the air, and water vapor. Why is there water vapor? Because the violet is wet. All plants transpire. It is a much more complicated arrangement than that of carbon dioxide; in fact, it is an enormously complicated arrangement.
Unfortunately, we cannot picture all that is really known about it chemically, because the precise arrangement of all the atoms is actually known in three dimensions, while our picture is in only two dimensions. All of the angles and distances are known. So a chemical formula is merely a picture of such a molecule. Figure How does the chemist find what the arrangement is?
He mixes bottles full of stuff together, and if it turns red, it tells him that it consists of one hydrogen and two carbons tied on here; if it turns blue, on the other hand, that is not the way it is at all. This is one of the most fantastic pieces of detective work that has ever been done—organic chemistry. To discover the arrangement of the atoms in these enormously complicated arrays the chemist looks at what happens when he mixes two different substances together.
The physicist could never quite believe that the chemist knew what he was talking about when he described the arrangement of the atoms. For about twenty years it has been possible, in some cases, to look at such molecules not quite as complicated as this one, but some which contain parts of it by a physical method, and it has been possible to locate every atom, not by looking at colors, but by measuring where they are. And lo and behold!
It turns out, in fact, that in the odor of violets there are three slightly different molecules, which differ only in the arrangement of the hydrogen atoms. One problem of chemistry is to name a substance, so that we will know what it is. Find a name for this shape! Not only must the name tell the shape, but it must also tell that here is an oxygen atom, there a hydrogen—exactly what and where each atom is.
So we can appreciate that the chemical names must be complex in order to be complete. You see that the name of this thing in the more complete form that will tell you the structure of it is 4- 2, 2, 3, 6 tetramethylcyclohexenyl butenone, and that tells you that this is the arrangement.
We can appreciate the difficulties that the chemists have, and also appreciate the reason for such long names.
It is not that they wish to be obscure, but they have an extremely difficult problem in trying to describe the molecules in words! How do we know that there are atoms? By one of the tricks mentioned earlier: we make the hypothesis that there are atoms, and one after the other results come out the way we predict, as they ought to if things are made of atoms. There is also somewhat more direct evidence, a good example of which is the following: The atoms are so small that you cannot see them with a light microscope—in fact, not even with an electron microscope.
With a light microscope you can only see things which are much bigger. Now if the atoms are always in motion, say in water, and we put a big ball of something in the water, a ball much bigger than the atoms, the ball will jiggle around—much as in a push ball game, where a great big ball is pushed around by a lot of people.
The people are pushing in various directions, and the ball moves around the field in an irregular fashion. Therefore, if we look at very tiny particles colloids in water through an excellent microscope, we see a perpetual jiggling of the particles, which is the result of the bombardment of the atoms. This is called the Brownian motion. We can see further evidence for atoms in the structure of crystals. Everything is made of atoms. That is the key hypothesis. The most important hypothesis in all of biology, for example, is that everything that animals do, atoms do.
In other words, there is nothing that living things do that cannot be understood from the point of view that they are made of atoms acting according to the laws of physics. This was not known from the beginning: it took some experimenting and theorizing to suggest this hypothesis, but now it is accepted, and it is the most useful theory for producing new ideas in the field of biology. If a piece of steel or a piece of salt, consisting of atoms one next to the other, can have such interesting properties; if water—which is nothing but these little blobs, mile upon mile of the same thing over the earth—can form waves and foam, and make rushing noises and strange patterns as it runs over cement; if all of this, all the life of a stream of water, can be nothing but a pile of atoms, how much more is possible?
If instead of arranging the atoms in some definite pattern, again and again repeated, on and on, or even forming little lumps of complexity like the odor of violets, we make an arrangement which is always different from place to place, with different kinds of atoms arranged in many ways, continually changing, not repeating, how much more marvelously is it possible that this thing might behave?
When we say we are a pile of atoms, we do not mean we are merely a pile of atoms, because a pile of atoms which is not repeated from one to the other might well have the possibilities which you see before you in the mirror.
We shall not discuss the history of how we know that all these ideas are true; you will learn these details in due time. The things with which we concern ourselves in science appear in myriad forms, and with a multitude of attributes. For example, if we stand on the shore and look at the sea, we see the water, the waves breaking, the foam, the sloshing motion of the water, the sound, the air, the winds and the clouds, the sun and the blue sky, and light; there is sand and there are rocks of various hardness and permanence, color and texture.
There are animals and seaweed, hunger and disease, and the observer on the beach; there may be even happiness and thought. Any other spot in nature has a similar variety of things and influences. It is always as complicated as that, no matter where it is.
Curiosity demands that we ask questions, that we try to put things together and try to understand this multitude of aspects as perhaps resulting from the action of a relatively small number of elemental things and forces acting in an infinite variety of combinations. For example: Is the sand other than the rocks? That is, is the sand perhaps nothing but a great number of very tiny stones?
Is the moon a great rock? If we understood rocks, would we also understand the sand and the moon? Is the wind a sloshing of the air analogous to the sloshing motion of the water in the sea? What common features do different movements have? What is common to different kinds of sound?
How many different colors are there? And so on. In this way we try gradually to analyze all things, to put together things which at first sight look different, with the hope that we may be able to reduce the number of different things and thereby understand them better.
A few hundred years ago, a method was devised to find partial answers to such questions. Observation, reason, and experiment make up what we call the scientific method.
We shall have to limit ourselves to a bare description of our basic view of what is sometimes called fundamental physics, or fundamental ideas which have arisen from the application of the scientific method. We do not know what the rules of the game are; all we are allowed to do is to watch the playing. Of course, if we watch long enough, we may eventually catch on to a few of the rules.
The rules of the game are what we mean by fundamental physics. Even if we knew every rule, however, we might not be able to understand why a particular move is made in the game, merely because it is too complicated and our minds are limited. If you play chess you must know that it is easy to learn all the rules, and yet it is often very hard to select the best move or to understand why a player moves as he does. So it is in nature, only much more so; but we may be able at least to find all the rules.
Actually, we do not have all the rules now. Every once in a while something like castling is going on that we still do not understand. Aside from not knowing all of the rules, what we really can explain in terms of those rules is very limited, because almost all situations are so enormously complicated that we cannot follow the plays of the game using the rules, much less tell what is going to happen next.
We must, therefore, limit ourselves to the more basic question of the rules of the game. There are, roughly speaking, three ways. First, there may be situations where nature has arranged, or we arrange nature, to be simple and to have so few parts that we can predict exactly what will happen, and thus we can check how our rules work. In one corner of the board there may be only a few chess pieces at work, and that we can figure out exactly.
A second good way to check rules is in terms of less specific rules derived from them. For example, the rule on the move of a bishop on a chessboard is that it moves only on the diagonal. One can deduce, no matter how many moves may be made, that a certain bishop will always be on a red square.
Of course it will be, for a long time, until all of a sudden we find that it is on a black square what happened, of course, is that in the meantime it was captured, another pawn crossed for queening, and it turned into a bishop on a black square. That is the way it is in physics. For a long time we will have a rule that works excellently in an overall way, even when we cannot follow the details, and then sometime we may discover a new rule.
From the point of view of basic physics, the most interesting phenomena are of course in the new places, the places where the rules do not work—not the places where they do work!
That is the way in which we discover new rules. The third way to tell whether our ideas are right is relatively crude but probably the most powerful of them all. That is, by rough approximation. While we may not be able to tell why Alekhine moves this particular piece, perhaps we can roughly understand that he is gathering his pieces around the king to protect it, more or less, since that is the sensible thing to do in the circumstances.
In the same way, we can often understand nature, more or less, without being able to see what every little piece is doing, in terms of our understanding of the game.
At first the phenomena of nature were roughly divided into classes, like heat, electricity, mechanics, magnetism, properties of substances, chemical phenomena, light or optics, x-rays, nuclear physics, gravitation, meson phenomena, etc.
However, the aim is to see complete nature as different aspects of one set of phenomena. That is the problem in basic theoretical physics today—to find the laws behind experiment; to amalgamate these classes. Historically, we have always been able to amalgamate them, but as time goes on new things are found. We were amalgamating very well, when all of a sudden x-rays were found. Then we amalgamated some more, and mesons were found.
Therefore, at any stage of the game, it always looks rather messy. A great deal is amalgamated, but there are always many wires or threads hanging out in all directions. That is the situation today, which we shall try to describe. Some historic examples of amalgamation are the following. First, take heat and mechanics. When atoms are in motion, the more motion, the more heat the system contains, and so heat and all temperature effects can be represented by the laws of mechanics.
Another tremendous amalgamation was the discovery of the relation between electricity, magnetism, and light, which were found to be different aspects of the same thing, which we call today the electromagnetic field. Another amalgamation is the unification of chemical phenomena, the various properties of various substances, and the behavior of atomic particles, which is in the quantum mechanics of chemistry.
The question is, of course, is it going to be possible to amalgamate everything, and merely discover that this world represents different aspects of one thing? Nobody knows. Whether there are a finite number of pieces, and whether there is even a border to the puzzle, are of course unknown. It will never be known until we finish the picture, if ever. What we wish to do here is to see to what extent this amalgamation process has gone on, and what the situation is at present, in understanding basic phenomena in terms of the smallest set of principles.
To express it in a simple manner, what are things made of and how few elements are there? Physics before It is a little difficult to begin at once with the present view, so we shall first see how things looked in about and then take a few things out of that picture. The elements on the stage are particles, for example the atoms, which have some properties.
First, the property of inertia: if a particle is moving it keeps on going in the same direction unless forces act upon it. The second element, then, is forces, which were then thought to be of two varieties: First, an enormously complicated, detailed kind of interaction force which held the various atoms in different combinations in a complicated way, which determined whether salt would dissolve faster or slower when we raise the temperature.
The other force that was known was a long-range interaction—a smooth and quiet attraction—which varied inversely as the square of the distance, and was called gravitation. This law was known and was very simple.
Why things remain in motion when they are moving, or why there is a law of gravitation, was, of course, not known. A description of nature is what we are concerned with here. From this point of view, then, a gas, and indeed all matter, is a myriad of moving particles. Thus many of the things we saw while standing at the seashore can immediately be connected.
First the pressure: this comes from the collisions of the atoms with the walls or whatever; the drift of the atoms, if they are all moving in one direction on the average, is wind; the random internal motions are the heat.
There are waves of excess density, where too many particles have collected, and so as they rush off they push up piles of particles farther out, and so on. This wave of excess density is sound.
It is a tremendous achievement to be able to understand so much. Some of these things were described in the previous chapter. What kinds of particles are there? There were considered to be 92 at that time: 92 different kinds of atoms were ultimately discovered. They had different names associated with their chemical properties. The next part of the problem was, what are the short-range forces? Why does carbon attract one oxygen or perhaps two oxygens, but not three oxygens?
What is the machinery of interaction between atoms? Is it gravitation? The answer is no. Gravity is entirely too weak. But imagine a force analogous to gravity, varying inversely with the square of the distance, but enormously more powerful and having one difference. Then what do we have? Suppose we have another charge some distance away. Would it feel any attraction? It would feel practically none, because if the first two are equal in size, the attraction for the one and the repulsion for the other balance out.
Therefore there is very little force at any appreciable distance. On the other hand, if we get very close with the extra charge, attraction arises, because the repulsion of likes and attraction of unlikes will tend to bring unlikes closer together and push likes farther apart. Then the repulsion will be less than the attraction.
This is the reason why the atoms, which are constituted out of plus and minus electric charges, feel very little force when they are separated by appreciable distance aside from gravity. The ultimate basis of an interaction between the atoms is electrical. Since this force is so enormous, all the plusses and all minuses will normally come together in as intimate a combination as they can. All things, even ourselves, are made of fine-grained, enormously strongly interacting plus and minus parts, all neatly balanced out.
Once in a while, by accident, we may rub off a few minuses or a few plusses usually it is easier to rub off minuses , and in those circumstances we find the force of electricity unbalanced, and we can then see the effects of these electrical attractions.
To give an idea of how much stronger electricity is than gravitation, consider two grains of sand, a millimeter across, thirty meters apart. If the force between them were not balanced, if everything attracted everything else instead of likes repelling, so that there were no cancellations, how much force would there be? There would be a force of three million tons between the two! You see, there is very, very little excess or deficit of the number of negative or positive charges necessary to produce appreciable electrical effects.
This is, of course, the reason why you cannot see the difference between an electrically charged and an uncharged thing—so few particles are involved that they hardly make a difference in the weight or size of an object.
With this picture the atoms were easier to understand. Now we go a little ahead in our story to remark that in the nucleus itself there were found two kinds of particles, protons and neutrons, almost of the same weight and very heavy. The protons are electrically charged and the neutrons are neutral.
If we have an atom with six protons inside its nucleus, and this is surrounded by six electrons the negative particles in the ordinary world of matter are all electrons, and these are very light compared with the protons and neutrons which make nuclei , this would be atom number six in the chemical table, and it is called carbon. Atom number eight is called oxygen, etc. So the chemical properties of a substance depend only on a number, the number of electrons.
The whole list of elements of the chemists really could have been called 1, 2, 3, 4, 5, etc. It is better to have names and symbols for these things, rather than to call everything by number. More was discovered about the electrical force. Six Easy Pieces by Richard P. Feynman - free mobi epub ebooks download.
I saw this book on San Francisco bookshelves, went through the phase of admiring Feynman, and finally decided to read his. It's nearly free of mathematics. It's probably illegal to use these sites but the probability of being caught is infinitesimal. Washington Square Press, , pp. Public works for water and power development and energy research appropriation bill, This set couples a book containing the six easiest chapters from Richard P.
This is my second time reading "Six Easy Pieces. If not, well, this book does hold it's own. The book was published in multiple languages including English, consists of pages and is available in Paperback format. Six Easy Pieces-Richard Feyman 2. In these classic lessons, Feynman introduces the general reader to the following topics: atoms, basic physics, energy, gravitation, quantum mechanics, and the relationship of physics to other topics. Filled with wonderful examples and clever illustrations, Six Easy Pieces is the ideal introduction to the fundamentals of physics by one of the most admired and accessible physicists of modern times.
For non-scientific readers eager to experience Richard Feynman's individual brand of science, this book and collection of audio CDs, featuring the Cited by: From Six Easy Pieces. Easy," she said, and then the phone rang. Or maybe it was the other way around.
Maybe the phone rang, and then Bonnie called my name. Bright sun shone in the window, and the skies were clear as far as I could see. There was a beautiful woman of the Caribbean lying next to : Washington Square Press.
0コメント