1. INTRODUCTION TO PHYSICS
What makes economic similar to other science subject like physics? Views How is cytosponge related to the science of Physics? Physics is related to chemistry in as much as chemical reactions are basically electromagnetic in nature. It can be plausibly argued that physics began with mechanics -- the science of machines produced his quantitative and general statement of the relationship. but this fact illustrates another very important aspect of the nature of physics -- an. Physics is the science of nature, or that which pertains to natural objects, To better understand this connection, it helps to refer to a solid working Because each of the other natural sciences biology, chemistry, geology, material science, .
Nevertheless, the conservation of total momentum mv was never violated in the collision of two objects. The statement of this principle involved two important concepts: Both of these concepts have been subjected to much discussion and refinement since those early days, but this fact illustrates another very important aspect of the nature of physics -- an acceptance of working hypotheses that are quite adequate at a particular stage in the development of the subject, but which are always liable to later modification.
Thus, for example, it was well known, even in the 17th century, that the Earth was not stationary, but was rotating on its axis and orbiting around the Sun, but both of these facts could be ignored in the analysis of laboratory-sized experiments on collisions. Only when larger-scale motions were involved did these facts become relevant; to introduce them at the beginning would make for unnecessary and obstructive complications. Another important but less general conservation principle was recognized at about the same time as the conservation of momentum.
It was limited to what are called elastic collisions, in which two colliding objects recoil from one another as vigorously as they approach. If one considers a collision along a straight line between two objects of masses m1 and m2, and if one denotes their initial and final velocities by u1, u2 and v1, v2, then the conservation of momentum is expressed by the equation: This held good whether the collision was elastic or inelastic less than perfect rebound.
But, if the collision was elastic, it was also true that the following relation held: In addition to these conservation principles, another fundamental physical principle applicable to collisions was recognized by Newton's great contemporary Christian Huygens This was what we would now call the equivalence of different frames of reference.
He argued that, by symmetry, they would recoil with their velocities reversed. He now imagined such a collision taking place on a boat that was itself moving at velocity v with respect to the shore Fig.
If this collision were observed by a man standing on the river bank, he would see it as a collision between a stationary sphere and one moving with velocity 2v.
In both cases the velocities as seen by the man on the bank would be interchanged by the collision. In other words, on the basis of the original symmetric collision one could predict the results of all collisions between these two objects occurring with the same relative initial velocity.
An elastic collision between two spheres as seen from two different reference frames. Underlying all these phenomena was another condition, never explicitly stated. This was that the total mass of the objects involved in a collision remained constant -- the principle of the conservation of mass. This was taken for granted in these physical systems, but an explicit statement of the conservation of mass, based on direct experiment, did not come until more than a century later, in chemistry, when Antoine Lavoisier established it for chemical reactions, involving much more drastic rearrangements of matter than did the collision experiments of Newton's contemporaries.
This is by no means the last we shall hear of conservation principles, but before continuing on that path we shall consider some other matters. On the left is the force; on the right is the mass multiplied by the acceleration produced in it by the force.
In other words, the left side is interpreted as a cause, and the right side as the effect produced by that cause. The two sides of the equation do not play equivalent roles. This is a feature that one does not find in the equations of mathematics. Nor are all physics equations of this type. Already in his time the science of optics was well developed, and Newton himself was a major contributor to it.
But then, during the 18th and 19th centuries, the knowledge of the physical world expanded to include such areas as heat, sound, electricity, and magnetism. Initially these, as well as mechanics and optics, were seen as separate fields of study, but then something very important happened: Sound, for example, came to be understood as the mechanical vibrations of air columns, strings, and so on, and heat as the chaotic mechanical motions of atoms and molecules for, although atoms as such could not be observed, there was a confident belief in their existence.
Along with this came a great enlargement of the concept of energy and its conservation. It came to be realized that, when mechanical energy apparently disappeared -- as for example in the inelastic collision of two objects -- one could account for the loss in terms of a transfer to the thermal energy of the colliding objects, as expressed in an increase of their temperature.
Thus conservation of energy came to be seen as a general principle, although the extension of it to electricity and magnetism did not happen immediately. Early in the 19th century, connections between the phenomena of electricity and magnetism were discovered: And then, toward the end of the century, the great physicist James Clerk Maxwell showed how, by uniting the equations that described electric and magnetic fields, he could account for the transmission of light through space at the amazing speed of about 3 x meters per second -- a value that was already known from experiment.
The net result was a tremendous unification of physics. For many years it had seemed that the diversity of physical phenomena was expanding almost without limit as new discoveries were made. Then it came to be seen that the divisions traditionally made between different areas of physics were really the result of our ignorance of their fundamental interconnections. As a matter of convenience, but perhaps unfortunately, these different areas continued to be treated for the most part as separate fields of study, and textbooks continued to be divided up accordingly.
This was not very serious, however, as long as it was recognized that, in a fundamental sense, physics was a single discipline. Perhaps the outstanding example of this is the attempt to find a successful model for the phenomena of light. According to some of the ancient Greeks, our ability to see an object depended on the emission of something from the eye -- an idea that should have been easily disprovable by experiment for example, the invisibility of an object in a darkened room.
Others, more plausibly, thought that an object became visible by virtue of particles of some sort emitted by the object itself. The production of sharp shadows by a small luminous source led naturally to the picture of light as consisting of particles traveling in straight lines from a source or from an object illuminated by it. This model was reinforced by the discovery of the law of reflection of a beam of light at a plane mirror -- angle of reflection equals angle of incidence.
Newton favored and supported this particle model. But his contemporary Huygens devised and promoted a very different model -- that light consists of waves traveling through a medium. He considered that the immense speed of light, and the ability of beams of light to pass through one another without any interaction, were evidence against light being composed of material particles.
Also he thought that vision must depend on the retina of the eye being shaken by the light. He was able to explain the rectilinear propagation of light as arising from the superposition of circular or spherical waves that originated from different points on the advancing wave-front of a beam.
It seemed obvious at the time that the particle and wave models of light were mutually exclusive. Thanks primarily to the great authority of Newton, the particle model became generally accepted, and remained unchallenged for about years.
But then something very astonishing happened. In about Thomas Young showed that a beam of light, if divided into two overlapping beams, showed the phenomenon of interference -- the production of alternating bright and dark regions on a screen placed to receive the light Fig.
The appearance of dark regions -- destructive interference -- was inconceivable on a particle model; how could one particle of light be annihilated by another?
Thus the particle model of light was abandoned, and evidence supporting a wave model of light continued to accumulate during the remainder of the 19th century. The culmination came when, as mentioned in the previous section, Maxwell showed that he could account for the propagation of light as an electromagnetic disturbance passing through a medium that was called the ether, and that was conceived as filling all space. The triumph of a wave model of light seemed complete and permanent, but this was not to be.
A schematic diagram of Young's two-slit interference experiment. Places where the waves from the two slits reinforce are shown by black dots, places where they cancel are shown by open circles.
The interference pattern has a central maximum and other maxima on each side. In practice the wavelength of the light is very small indeed compared to the spacing of the slits; this means that the interference fringes are extremely numerous and very close together. Its primary ingredients were absolute space and time, the causal laws of mechanics, electricity and magnetism embodying a wave model of lightand a picture of matter as consisting of discrete and indivisible particles obeying these laws.
But such complacency was about to be shattered. In the space of less than 10 years came radioactivity, the discovery of the electron, the quantum of energy, and special relativity; each of them, in its way, called for a drastic revision of our picture of the physical world.
The source of these emissions and their energy was a great puzzle, and it was at one stage suggested that the principle of the conservation of energy would have to be abandoned. Further research showed that this was not necessary, but an even more precious principle had to be sacrificed: For it came to be clear that, in a group of identical radioactive atoms, the times at which they underwent a change to a different kind of atom were quite random; there was nothing, so far as could be discovered, that caused a particular atom to undergo a radioactive change at a particular time; the atoms decayed spontaneously and independently.
This was established in an experiment by Ernest Rutherfordthe dominant figure in the early days of nuclear physics. But physics did not cease to be an exact science with immense predictive power.
We shall have more to say about this later. This became possible, in large part, because of the development of efficient ways of producing vacuum -- a good example of how advances in technology directly affect the progress of fundamental physics. A whole range of new phenomena came into view. Perhaps the most dramatic of these was the discovery of x rays by Wilhelm Conrad Roentgen The ability of these rays to penetrate the human body and expose its internal structure was quickly exploited.
At first the nature of these rays was a mystery, but after a few years it was established that they were electromagnetic waves, like light but of a much shorter wavelength by a factor of about But behind these x rays lay something destined to have a much greater influence on the course of physics. They were produced by the impact on a solid "target" of so-called cathode rays, emitted from a negatively charged electrode in an evacuated tube. What were these cathode rays?
It was Joseph John Thomson who found that they were negatively charged particles with a far smaller mass, in relation to their charge, than any particle previously known.
Furthermore, their properties did not depend at all on the material used as the cathode negative electrode from which they came. The implication was that all atoms had an internal structure that included these novel particles, which of course we know today as electrons. The old idea of atoms as indivisible the Greek basis of their name was gone forever. The question naturally arose: That question was not properly answered for more than another 10 years, when Rutherford found that the positive part of the atom was a nucleus smaller in diameter by a factor of about 10, than the atom as a whole.
We shall return to that development in the next section of this article. Well before then, it had come to be realized that radiant heat was a form of electromagnetic radiation, which became visible when an object was sufficiently hot but also included radiation at much longer wavelengths.
The spectrum of such radiation intensity versus wavelength for a body at a particular temperature was a rather uninteresting-looking curve Fig. Attempts to explain this spectrum in terms of the basic classical theory of electromagnetic radiation-- a well understood theory -- did not work at all well.
A qualitative graph of intensity versus wavelength or frequency for the radiation from a hot body. As the temperature is raised, the overall amount of radiation increases and the peak shifts toward shorter wavelength higher frequency. The German physicist Max Planck set himself the task of finding a better fit.
Thus the quantum was born. Planck shrank from proposing that the radiation itself was quantized -- the classical wave theory of light still stood supreme -- but Albert Einstein advanced this hypothesis in what he called a heuristic way something that works but may not be the last word in Its consequences were very far-reaching; we shall come to that later. Ever since the time of Newton, it had been accepted that space and time were absolute, even though Newton himself acknowledged that we could not identify absolute space and had to content ourselves with the study of relative motions.
But then, inEinstein came forward with his revolutionary proposal that neither time nor space was absolute, that they were related to one another, and that both depended on measurements made with respect to a chosen frame of reference, which had to be identified. This meant, in particular, that one could not state categorically that two events occurring at different places were simultaneous; the judgment as to whether they were simultaneous or not depended on the frame of reference that one was in.
Physics: The Science of the Universe and Everything In It | shizutetsu.info
This theory -- the special theory of relativity -- is not basically difficult or complicated; in a simplified form, it can be presented with nothing more than high-school algebra. Its challenge is a conceptual one, because it requires us to abandon intuitive ideas that all of us grow up with. It is no trivial matter to make such an adjustment, but it soon became clear to Einstein's contemporaries at least, to many of them that the new theory had a predictive power that could not be denied.
The slowing down of a clock that is in motion with respect to us, for example, might seem to be science fiction -- and in the form of the "twin paradox" with a human traveler staying young, while his brother on Earth gets old, it is; nevertheless, the basic effect has been directly confirmed by observations using precise atomic clocks transported around the Earth in commercial jet aircraft. One aspect of relativity that was particularly troubling to the traditionalists was its denial that there existed a single preferred frame of reference.
Physics: The Science of the Universe and Everything In It
Such a frame was assumed to be defined by what Huygens called the ether -- the hypothetical medium that was deemed to be essential as the carrier of light and all other kinds of electromagnetic waves. The notion of waves that did not require any material medium to carry their vibrations was regarded as an absurdity.
But the failure of all experiments to detect the motion of the Earth through this medium was one of the important supports for the correctness of Einstein's ideas. Physicists had to get used to the idea that electromagnetic waves did not need a medium to wave in; this picture was required only if one demanded a purely mechanical model of the wave propagation.
In the latter part of the 19th century, much effort was expended on creating such mechanical models, until Einstein made them superfluous.
This is the key substance which is passed from one cell to another for instance sperm cells consist mostly of DNA and carries the information as to how to make the enzymes.
First, the blueprint must be able to reproduce itself. Secondly, it must be able to instruct the protein. Concerning the reproduction, we might think that this proceeds like cell reproduction. Cells simply grow bigger and then divide in half. Must it be thus with DNA molecules, then, that they too grow bigger and divide in half? Every atom certainly does not grow bigger and divide in half!
No, it is impossible to reproduce a molecule except by some more clever way.
Schematic diagram of DNA. The structure of the substance DNA was studied for a long time, first chemically to find the composition, and then with x-rays to find the pattern in space. The result was the following remarkable discovery: The DNA molecule is a pair of chains, twisted upon each other. The backbone of each of these chains, which are analogous to the chains of proteins but chemically quite different, is a series of sugar and phosphate groups, as shown in Fig.
Thus perhaps, in some way, the specific instructions for the manufacture of proteins are contained in the specific series of the DNA. Attached to each sugar along the line, and linking the two chains together, are certain pairs of cross-links.
Whatever the letters may be in one chain, each one must have its specific complementary letter on the other chain. What then about reproduction? Suppose we split this chain in two. How can we make another one just like it? This is the central unsolved problem in biology today. The first clues, or pieces of information, however, are these: There are in the cell tiny particles called ribosomes, and it is now known that that is the place where proteins are made. But the ribosomes are not in the nucleus, where the DNA and its instructions are.
Something seems to be the matter. However, it is also known that little molecule pieces come off the DNA—not as long as the big DNA molecule that carries all the information itself, but like a small section of it. This is called RNA, but that is not essential. It is a kind of copy of the DNA, a short copy. The RNA, which somehow carries a message as to what kind of protein to make goes over to the ribosome; that is known.
When it gets there, protein is synthesized at the ribosome. That is also known. However, the details of how the amino acids come in and are arranged in accordance with a code that is on the RNA are, as yet, still unknown.
We do not know how to read it. Certainly no subject or field is making more progress on so many fronts at the present moment, than biology, and if we were to name the most powerful assumption of all, which leads one on and on in an attempt to understand life, it is that all things are made of atoms, and that everything that living things do can be understood in terms of the jigglings and wigglings of atoms.
Astronomy is older than physics. In fact, it got physics started by showing the beautiful simplicity of the motion of the stars and planets, the understanding of which was the beginning of physics.
But the most remarkable discovery in all of astronomy is that the stars are made of atoms of the same kind as those on the earth. Atoms liberate light which has definite frequencies, something like the timbre of a musical instrument, which has definite pitches or frequencies of sound. When we are listening to several different tones we can tell them apart, but when we look with our eyes at a mixture of colors we cannot tell the parts from which it was made, because the eye is nowhere near as discerning as the ear in this connection.
However, with a spectroscope we can analyze the frequencies of the light waves and in this way we can see the very tunes of the atoms that are in the different stars. As a matter of fact, two of the chemical elements were discovered on a star before they were discovered on the earth.
Helium was discovered on the sun, whence its name, and technetium was discovered in certain cool stars. This, of course, permits us to make headway in understanding the stars, because they are made of the same kinds of atoms which are on the earth.
Now we know a great deal about the atoms, especially concerning their behavior under conditions of high temperature but not very great density, so that we can analyze by statistical mechanics the behavior of the stellar substance.
Even though we cannot reproduce the conditions on the earth, using the basic physical laws we often can tell precisely, or very closely, what will happen. So it is that physics aids astronomy. Strange as it may seem, we understand the distribution of matter in the interior of the sun far better than we understand the interior of the earth. What goes on inside a star is better understood than one might guess from the difficulty of having to look at a little dot of light through a telescope, because we can calculate what the atoms in the stars should do in most circumstances.
One of the most impressive discoveries was the origin of the energy of the stars, that makes them continue to burn. One of the men who discovered this was out with his girlfriend the night after he realized that nuclear reactions must be going on in the stars in order to make them shine. She was not impressed with being out with the only man who, at that moment, knew why stars shine.
Well, it is sad to be alone, but that is the way it is in this world. Furthermore, ultimately, the manufacture of various chemical elements proceeds in the centers of the stars, from hydrogen.
How do we know? Because there is a clue. The proportions are purely the result of nuclear reactions.
By looking at the proportions of the isotopes in the cold, dead ember which we are, we can discover what the furnace was like in which the stuff of which we are made was formed. Astronomy is so close to physics that we shall study many astronomical things as we go along. First, meteorology and the weather.
Of course the instruments of meteorology are physical instruments, and the development of experimental physics made these instruments possible, as was explained before. However, the theory of meteorology has never been satisfactorily worked out by the physicist. It turns out to be very sensitive, and even unstable. If you have ever seen water run smoothly over a dam, and then turn into a large number of blobs and drops as it falls, you will understand what I mean by unstable.
You know the condition of the water before it goes over the spillway; it is perfectly smooth; but the moment it begins to fall, where do the drops begin? What determines how big the lumps are going to be and where they will be? That is not known, because the water is unstable. Even a smooth moving mass of air, in going over a mountain turns into complex whirlpools and eddies.
In many fields we find this situation of turbulent flow that we cannot analyze today. Quickly we leave the subject of weather, and discuss geology! The question basic to geology is, what makes the earth the way it is? The most obvious processes are in front of your very eyes, the erosion processes of the rivers, the winds, etc.
It is easy enough to understand these, but for every bit of erosion there is an equal amount of something else going on. Mountains are no lower today, on the average, than they were in the past. There must be mountain-forming processes.
You will find, if you study geology, that there are mountain-forming processes and volcanism, which nobody understands but which is half of geology. The phenomenon of volcanoes is really not understood. What makes an earthquake is, ultimately, not understood.
It is understood that if something is pushing something else, it snaps and will slide—that is all right. But what pushes, and why? The theory is that there are currents inside the earth—circulating currents, due to the difference in temperature inside and outside—which, in their motion, push the surface slightly.
Thus if there are two opposite circulations next to each other, the matter will collect in the region where they meet and make belts of mountains which are in unhappy stressed conditions, and so produce volcanoes and earthquakes.
What about the inside of the earth? A great deal is known about the speed of earthquake waves through the earth and the density of distribution of the earth.
THE NATURE OF PHYSICS
However, physicists have been unable to get a good theory as to how dense a substance should be at the pressures that would be expected at the center of the earth. In other words, we cannot figure out the properties of matter very well in these circumstances. We do much less well with the earth than we do with the conditions of matter in the stars. The mathematics involved seems a little too difficult, so far, but perhaps it will not be too long before someone realizes that it is an important problem, and really works it out.
The other aspect, of course, is that even if we did know the density, we cannot figure out the circulating currents. Nor can we really work out the properties of rocks at high pressure.
Incidentally, psychoanalysis is not a science: The witch doctor has a theory that a disease like malaria is caused by a spirit which comes into the air; it is not cured by shaking a snake over it, but quinine does help malaria.
So, if you are sick, I would advise that you go to the witch doctor because he is the man in the tribe who knows the most about the disease; on the other hand, his knowledge is not science. Psychoanalysis has not been checked carefully by experiment, and there is no way to find a list of the number of cases in which it works, the number of cases in which it does not work, etc.
The other branches of psychology, which involve things like the physiology of sensation—what happens in the eye, and what happens in the brain—are, if you wish, less interesting. Physics is the branch of science which deals with matter and its relation to energy.
It involves study of physical and natural phenomena around us. Examples of these phenomena are formation of rainbow, occurrence eclipse, the fall of things from up to down, the cause of sunset and sunrise, formation of shadow and many more. Physics as a subject is divided into six broad branches as discussed below. Under this branch, we look into details the aspects of linear, circular and oscillatory motions as well as motion of fluids ii Geometrical Optics This branch takes a keen look at the behavior of light in various media.
Relationship between physics and otheir subjects Physics does not only relate the remaining two science subjects but also enjoys a relationship with other subjects as well.
Many physics formulae are expressed mathematically.