Basic Of Engineering

Engineering materials - Ferrous metals

2015-06-30T12:37:00.000-07:00

Engineering materials - Ferrous metals

Engineering materials - selection

In the design of machinery in general, a vast variety of materials of both organic and inorganic origin is utilized. We generally think of metals as the usual materials of design, but, although used to a lesser degree, such materials as wood, leather, rubber, and other plastics have widespread use, and others, such as fabrics, cork, special minerals, etc., have limited use.

In making a selection of a material we must first decide what constitutes a "proper materials". A proper material may be defined as one which best performs the functions required with the least total cost. This does not mean that the material having the lowest unit cost is best, because a more expensive material may permit reduction of weight, eaier heat tretment or fabrication, or it may process other advantages that make the final result less costly. And at times, of course, luxury, aooearance, or extreme safety is desired even at great expense.

Designers are interested principally in the physical properities and the cost of the finished part, and only incedentally in the chemical constituents and methods of preparation from the raw material. The physical properities of most importance are strenght, regidity, resistance to corrosion and to fatigue failure, and in some cases, weight. Other properities that may be of importance are hardness, impact resistance, heat and electrical conductivity, wear resistance, low friction, machinability, and weldability, When several of these characteristics are desired simultaneosly, selection of the most suitable and the most economical material is sometimes difficult.

Ferrous metals - Iron.

In general, we may say that certain groups of materials are used mainly because they are abundantly available and cheap. This condition is particularly true of the ferrous group of metals.

Ferrous metals are the most commonly used, and, with proper alloying and treatment, they may be adapted to almost all simple needs. The advantages of iron as a base metal, in addition to its abundance and low cost, are its strength and its adaptability to fabrication. It may be readily cast, forged, machined, and welded. Principal limitations are its weight and its susceptibility to corrosion.

Plain carbon steels

Steel differs from cast iron in that it has no carbon in free state. The percentage of carbon varies from 0.08 to 1.5 with consequent differences in properities. Steel is classified according to carbon content approximately as follows: "Very mild", "mild", or "low carbon"; "medium carbon", and "high carbon" or "hard". Both low and medium-carbon steels are generally used for machine parts, whereas high-carbon steels are used for springs or tools. Low-carbon steels are readily welded and foged since they are plastic over an extensive temperature range. They are very ductile and hence are resistant to shock and impect, but are not responsive to heat treatment by quenching. Medium-carbon steels are more difficult to forge and weld, but tensile strenght and elastic limit can be increased considerably by quenching at the expense of lessened ductility. High-carbon steels are difficult to forge and weld but may be hardened to a good cutting edge by quenching.

Alloy steels.

When metals are dissolved in each other and then solidified, an alloy results. Alloy steel is obtained when the other elements added to the iron and carbon are in sufficient quantities to influence the physical properities. Practically all alloy steels must undergo special heat treatment to obain the properities desired. The alloying elements used in steel are as follows: Nickel, silicon, chromium, vanadium, tungsten, molybdenum, manganese, and copper.

Several of these may be used simultaneously to obtain special physical properities when given a double heat treatment, High elastic limit with ample ductility, hard wearresisting surfaces combined with high core strength and toughness, high impact and fatigue resistance, are some of the properities that are readily attainable.

Engineering mechanichs - Part two

2015-06-22T05:37:00.000-07:00

Engineering mechanichs - Part two

Statics

Static deals with the conditions of equilibrium of bodies acte upon by forces and is one of the oldest branches of science. When several forces of various magnitudes and directions act upon a body, they are said to constitute a system of forces. The general problem of statics consist of finding the conditions that such a system must satisfy in order to have equilibrium of the body. The various methods of solution of this problem are based on several axioms, called the principles of statics, which are given here in brief.

Parallelogram law

If two forces, represented by vectors AB and AC, acting under an angle α, are applied to a body at point A, their action is equivalent to the actionof one force represented by the vector AD, obtained as the diagonal of the parallelogram constructed on the vectors AB and AC.

Equilibrium law

Two concurrent forces can be in equilibrium only of their resultant is zero. This will be the case if we have two forces of equal magnitude acting in opposite directions along the same line. We shall now generalize this conclusion as the second principle of statics, usually called the equilibrium law: Two forces can be in direction, and collinear in action.

Law of superposition

When two forces are in equilibrium (equal, opposite, and collinear), their resultant is zero and their combined action on a rigid body is equivalent to that of no force at all. A generalization of this observation gives us the third principle of statics, sometimes called the law of superposition: The action of a given system of forces on a rigid body will in no way be changed if we add to or subtract from them another system of forces in equilibrium.

Law of action and reaction

Very often we have to investigate the conditions of equilibrium of bodies that are not entirely free to move. Restriction to the free motion of a body in any direction is called constraint. A body that is not entirely free to move and is acted upon by some applied force (of forces) will, in general, exert pressures against its supports. These actions of a constrained body against its supports induce reactions from the supports on the body, and as the fourth principle of statics we take the following statement: Any pressure on a support causes an equal and opposite pressure from the support so that action and reaction are two equal opposite forces.

Kinematics and kinetics

In statics we have considered rigid bodies that are rest. In dynamic we shall consider bodies that are in motion. For convenience, dynamics is comonly divided into two branches called kinematics adn kinetics. In kinematics we are concerned only with the space-time relationship of a given motion of a body and not at all with the forces that cause the motion. If we see that a wheel rolls along a straight level track with uniform speed, the determination of the shape of the path described by a point on its rim and of the position along this path that the chosen point will occupy at any given instant are problems of kinematics.

In kinetics we are concerned with finfing the kind of motion that a given body or system of bodies will have under the action of given forces, or with what forces must be applied to produce a prescribed motion. If a constant horizontal force is to be applied to a given body that reset on a smooth horizontal plane, the prediction of the way in which the body will move is a problem of kinetics.

The whole science of dynamics is based on the natural laws governing the motion of a particle under the action of a given force. Whenever a particle moves through space, it describes a curve that is called the path. The path of a particle may be either a pace curve, called a tortuous path, or a plane curve, called a plane path. In the simplest case the path will be a straight line, and the particle is said to have rectilinear motion. This can be uniform of nonuniform. If the rectilinear motion of a particle is nonuniform, its velocity is changing with time and we have acceleration. In the case of uniform motion, however, the velocity remains constant describes a curved path, it is said to have curvilinear motion.

Engineering mechanics - Part one

2015-06-22T04:07:00.003-07:00

Engineering mechanics - Part one

The importance of mechanics in the preparation of young engineers for work in specialized fields cannot be overmphasized. The demand from industry is more and more for young men who are soundly grounded in their fundamental subjects rather than for those with specialized raining. There is good reason for this trend: The industrial engineer is continually being confronted by new problems, which do not always yield to routine methods of solution. The man who can successfully cope with such problems must have a sond understanding of the fundamental principles that apply and be familiar with various general methods of attack rather than proficient in the use of any one. It seems evident, then, that university training in such a fundamental subject as mechanics mus seek to build a strong foundation, to acquaint the student with as many general methods of attack as possibile, to illustrate the application of these methods to practical engineering problems, but to avoid routine drill in the manipulation of standardized methods of solution.

The solution of a problem in mechanics usually consists of three steps:

The reduction of a complex physical problem to such a state of idealization that it can be expressed algebraically or geometrically;
The solution of this purely mathematical problem;
The interpretation of the results of the solution in terms of the given physical problem. It is too often the case that the student's attention is called only to the second step so that he does not see clearly the connection between this and the true physical problem.

Rigid body

We shall be mostly concerned in engineering mechanics with problems involving the equilibrium of rigid bodies. Physical bodies, such as we have to deal with in the design of engineering structures and machine parts, are never absolutely rigid but deform slightly under the action of loads which they have to carry.

Force

For the investigation of problems of statics we most introduce the concept of force, which may be defined as any action that tends to change the state of rest of a body to which it is applied. There are many kinds of force, such as gravity force, with which we are all familiar, and the simple push or pull that we can exert upon a body with our hands. Other examples of force are gravitational atraction between the sun and planets, the tractive effort of a locomotive, the force of magnetic attraction, steam or gas pressure in a cylinder, win pressure, atmospheric pressure and frictional resistance between contiguous surfaces.

Characteristics of a force

For the complete definitions of a force we must know 1 its magnitude, 2 its point point of application, and 3 its direction. These three quantities, which completely define the force, are called its characteristics or specifications.

The magnitude of a force is obtained by comparing it with a certain standard, arbitarily taken as the poundm which represents the weight of a certain platinum cylinder kept in the Tower of London. The magnitudes of forces are commonly measured by using various kind of dynamometers.

The point of application of a force acting upon a body is thet point in the body at which the force can be assumed to be concentrated. Physically, it will be impossible to concentrate a force at a single points; that is, every force must have some finite area or volume over which its action is disturbed. However, we often find it convenient to think of such disturbed force as being concentraded at a single point of application wherever this can be done without sensibily changing the effect of the force on the contitions of equilibrium. In the case of gravity force disturbed throught the volume of a body, the ooint of application at which the total weight can be assumed to be concentrated is called the center of gravity of the example is always directed vartically downward.

Descriptive geometry and mechanical drawing

2015-06-21T17:35:00.000-07:00

Descriptive geometry and mechanical drawing

Descriptive geometry

Is a mathematical-graphical procedure that has for its purpose the visualization of structures and their exact representation in drawings. After analysic of any structure, each element is shown in the drawing in its exact geometrical relation to the other elements.

The basic methods of descriptive geometry are the projection method and the direct method. There are two general types of views, perspective and orthographic. A perspective view is observed from a fixed station point, or point of view, by means of converging rays of light that meet at the eye of the observer. An orthogographic view of an object is observed in a chosen direction by means of paralel rays of light.

Mechanical drawing

Language is a defined as the expression of thought. But if we attempt to describe in words the appearance and details of a machine, or bridge, or building, we find it not only difficult but in most cases impossible. Here we must use another language, the universal graphic language of drawing.

A writen description of a new machine part would have to be very long to tell about it and even then might be misunderstood. A picture of it would serve the purpose much better, but the picture would not show the exact method of construction. It would gove only the external appearence without telling what was inside. It would be impossible to construct a locomotive or an airplane from either a word description or a picture.

Fortunately, another form of description has been developed by which the exact shape of every detail of any structure may be defined accurately and quickly. This method consist of the making of a series of views arranged according to a definite system, with figures added to tell the sizes. This is know as "mechanical drawing" and it forms so important a part of all undustrial an mechanical work that it is called the "language of industry".

Shape description

There are two things that a deigner, invertor or builder must be able to do:

first, he must be able to visualize what an object looks like without actually having the objects;

second, he must be able to describe it so that it could be built.

His problem then is how to represent solid objects on a sheet of paper in such a manner as to tell the exact shape. This is done drawing a system of views of object as seen from different positions..

A picture of an hydraulic jack for an automobile (fig. 1) shows this tool as it ordimarily appears to us, but it does not show the true shapes of the parts. The top of the cylinder appears as an ellipse, although we know it really is circular. If we look down at the jack from above, we obtain a view showing the exact shape of the cylinder, and the outline of the other parts as seen above. This is called a top view or plan. This view deos not tell us the height of the jack, so it is necessary to take another view from a postition directly in front view or side viewm to show the height, is added. Often, as in this case, both the front and side views, in addition to the top view, are needed to describe the object (fig. 2). The three views taken together completely define the shapes of all visible parts of the jack and their exact relations to each other.

Sometimes a left-side view describes the object or construction more clearly than the tight-side view and in such cases it should be used. It is sometimes desirable or necessary to show the rear view or the bottom view of an object. Views can then be projected to all six faces or planes of an object.

Sections

We know that the parts of an object that cannot be seen are repesented by hidden lines composed of short dashes.

This method is satisfactory where the object is solid or the interior simple. There are many cases, especially where there is considerable interior detail or where several pieces are shown together, in which the hidden lines become confusing or hard to read. This diffictly is avoided by using a sectional view. A sectional view is obtained by supposing the piece to be cut apart by an imaginary cutting plane, and the front part removed, thus exposing the interior.

Power and Efficiency

2015-06-21T16:24:00.002-07:00

Power and Efficiency

Rate of doing work: power

In practice, where work is done upon a body, both the amount of work and also the time during which that work is done are important. For example, if a motordriven soist has to raise its load quikly, a more powerful hoist and a larger driving motor are needer than if more time were allowed. Usually the size of machinery is determined, not by the total amount of work to be done, but by the rate ar which it to be done; that is, the amount of work required per unit of time, The time rate of doing work is caled power.

Since power is the time rate of doing work, the unit for power in any system of units is found by dividing the work unit in that system by the time unit. Thus, in the Sl system, power is expressed in watts, and in the British gravitational system it is expressed in foot-pounds (pound-force feet) per second.

In addition to the units of the standard systems, other practical units are in general use. The horsepower (hp) is the power prowided by an agent while doing work at the rate of 33 000 (ft x lb)/min. , or 550 (ft x lb)sec. The watt is a rate of doing work equal to l joule/sec. The kilowatt (kw) is a power unit used in rating electric machines.

Simple machines

It is a matter of common expirience that a stone firmly embedded in the ground can be dislodged with a crowbar, and that a heavy automobile can be raised by means of a jack. The crowbar or jack serves as an intermediate device upon which work can be done and which in turn does work upon some other object. A device that accomplishes this results is technicall called a machine. The complex machines used in industry are found upon analysis to be made up largely of certain elements that maybe considered simple machines in themselves. These simple machines comprise the lever, the wheel and axle, the pulley, the inclined plane, the screw, and the wedge.

Ushually a machine is epmployed order to lessen the force required in doing a certain piece of work. Thus, if a 500-lb weight is to be lifted, a machine can be used to exert this amount of upward force upon it while the person operating the machine exerts perhaps only 50 pounds. It is thus possible, and indeed usual, to obtain a larger force from a machine than that which is exerted upon it. Of course, this statement applies to force and not to energy; according to the law of conservation of energy, more work cannot be obtained from a machine than the energy supplied to it. Since work = force x distance, when the operator exerts a smaller force thandoes the machine, he exerts the smaller force through a correspondingly greater distance.

The ratio of the force extred by a machine on a load to the force extred by an operator on the machine is called the mechanical advant of the machine.

Efficiency of a machine. Friction is present in all moving machinery, however well designed; consequently, the energy delivered by a machine is less than that supplied to it. More definitely, the principle of conservation of energy, of energy shows that

energy input = energy output + energy wasted

if no energy is stored up in the machine, Since energy used per unit time is power, it can also be said that

power input = power output + power wasted.

The efficiency of machine is defined as the ratio of its output to its input, both input and output being expressed in the same units of energy or power. The ratio of output to input is always less than unity; in practice, it is usually multiplied by 100 and expressed in per cent. High efficiency in a machine implies that in a given time a largde part of the energy supplied to it is delivered by the machine to its loadand a small part wasted. The efficiency of a large electric generator may be as high as 98 per cent. In some of the simple machines - a screw jack, for exapmle - considerable friction is necessary to prevent the load from running down after it has been raised; because of the energy wasted in friction the efficiency of a terms of their output; thus, a 5-hp motor is one that can deliver 5 hp without exceeding its design limitaions; if its efficiency is 80 per cent, the power input to machine is 5 hp/0.80 - 6.25 hp.

Nuclear Energy

2015-06-21T14:20:00.000-07:00

Nuclear Energy

The fundamental source of power

In the last fifty years we have learned more about the fundamental structure of metter than in all history. Today we know that the rearrangement of the particles comprising the atom accounts for all the energy in the universe. And we are just beginning to learn how to capture and make use of some of that energy.

To illustrate this relationship between matter and energy let us consider what happens to a simple material such as carbon when it is burned. Each carbon atom, like all atoms, consists of a compact central nucleus made up of various heavy particles called nucleons, surrounded by lighter particles called electrons.

Electrons surround the nucleus in somewhat the samo manner as planets circle around the sun.

For years we were taught a fundamental rule, "Matter cannot be created or destroyed". When carbon is burned in oxygen, the weight of the carbon dioxide gas given off in the burning reaction seems to be exactly the same as that of the oxygen and carbon beforehand. The energy given off as heat was explaines as chemical energy inherent in the two materials.

Einstein introduced a new concept

Albert Einstein was the first man to offer a more satisfactory explanation for the interrelationship between matter and energy as part of his Theory of Relativity. He concluded that matter and energy were interchangeable and that the relationship between them could be expressed by the equation:

Energy = (Mass) x (Velocity of Light)²

In this key equation, the value of the velocity of light, which is always constant, is so large a very small change in mass is equivalent to an almost incredible amount of energy,

The vast amount of research preceding the first atomic bomb, as well as the bomb itself, offered dramatic proof of Einstein's Theory. If this equation is applied to the burning of one pound of carbon, we can calculate thet the heat energy given off is equivalent to only four ten-billionths of a pound, a weight loss so small that no instruments are able to detect it.

The burning of carbon is a typical example of a chemical reaction. There are countless examples of chemical reaction in our everyday lives and in industry. In all these reactions, only the outermost electrons of the atoms are disturbed. As a result, only an immeasurably small change in mass takes place, and only a relatively small amount of energy is given off.

Two kinds of nuclear reactions

In the case of nuclear reactions, the heavy nucleus of the atom is changed and far greater amounts of energy are liberated. There are two omportant kinds of nuclear reactions: nuclear fusion and nuclear fission.

In nuclear fusion two or more relatively light nuclei combine to become a single nucleus which weights less than the sum of the weights of the parent nuclei. Tremendous amounts of energy are released in this process. Temperatures in the millions of degrees are required before the fusion reaction can take place Fusion is bolieved to be the source of the sun's energy, with hydrogen nuclei continuosly combining to form helium nuclei.

The first fusion reaction initiated by man was the hydrogen bomb. Controlled fusion, when it is commercially achieved some day, may become one of the most important developments in history because it will furnish almost limitless amounts of energy from fuels that are plentiful.

The second type of reaction is nuclear fission, in which a heavy nucleus splits into two or more fragments. The total weight of all the fragments is somewhat less than the weight of the parent nucleus, and energy is released in proportion to this weight loss. The nuclei of some of the heavier metals like plutonium, and types of uranium and thorium, are especially suited to this type of reaction. In the fission of these nuclei, certain particles are ejected which cause fission of neighboring nuclei, thus sustaining the reaction.

The explosion of an atom bomb is an example of nuclear fission which is allowed to occur at very rapid rate. However, nuclear fission has already begun serving mankind in peaceful ways through power reactors. In the reactor, energy from of heat, which is used to convert water to steam. The steam turns a turbine generator which generates electricy in exactly the same way as in the conventional steam power plant.

Work and energy

2015-06-21T12:39:00.000-07:00

Work and energy

Work

Work is applied to any form of labor, pysical or mental, for producing any kind of result. In science and engineering, on the other hand, "work" has a definite technical meaning, which the following illustration will make clear.

When a man moves a box along the floor by a steady push, or raises it from the floor to the top of a table, two things should be noted: first, that the men exerts a force on the box, and second, that the box undergoes a displacement in the direction of the force. Under these contiditions the man or the force that the exerts is said to do work on the box.

The amount of work done is the product of the force and the displacement of the object while the force is being applied. In symbols, when a constant force F is exerted on an object while the object undergoes a displacement D in the direction of the the forcem the amount of work done on the object is W=FD .

Energy

A body is said to possess energy if it is able to do work. For example, a man or horse can do work and so possess energy; the steam within the cylinder of a steam engine possesses energy since it is able to move the piston; the mainspring of a watch possesses energy when woundn since it is able to drive the hands of the timepiece. Moreover, when a body does work, its energy is reduced by an amount exactly equal to the work done, Work and energy are expressed in the same units.

There are many different forms of energy; thus, the spring just mentioned has mechanical energy, a hot substance has internal energy, coal has chemical energy, a charged capacitor has electrical energy, and so on. A body or a system of bodies may posses mechanical energy from either or both of two causes. First, whenever a body is in motion it is able to exert a force and do work in coming to rest; a moving body always posses energy by virtue of its motion; this is called kinetic energy. A moving hammer has kinetic energy, and this enables it to do work in driving a nail. Second, a body that has been moved to a new position is sometimes able to do work because of this fact; for example, a raised weight can do work in falling and is commonly said to posses energy by virtue of its position; this is called potential energy.

Conservation and transformation of energy

Whenever a body does work, its capability of doing further work is lessened, and this means that it possesses less energy than before. This reduction must not be regarded as a loss of energy, for in doing work the body has imparted an equal amount of energy to some other body, which, together with the first, constitutes a system. The energy given up by a body is imparted to others without loss, and thus within the system the total amount of energy remains unchanged. This illustrates a basic principle know as the conservation of energy, which states that energy can neither be created nor destroyed. Expressed differently, the total amount of energy in the universe remains constant.

Although energy can be transformed from one kind to another, it is not destroyed in the process. When energy is expended in work against friction, it is said to be wasted, thats is, rendered unavailable for useful purposes; but it is not destroyed, for it is converted into heat, which is recognized as form of energy.

Energy sources

This is the term aplied to the sources from which energy can be obtained to provide heat, light, and power.

Industrial society has based largely on the substitution for animal energy of power from heat of combustion of carboniferous fuels. It seems likely that it will be based in the future largely on heat from the sun and heat which is generated by nuclear reactions.

Major carboniferous fuels are coal, petroleum, and natural gas - all fossil materials formed in finite amounts many millions of years ago. Other important fossil fuels are oil shales and tar sands. Minor fuels are forms of current production of vegetation,

Nonfuel sources of energy are water, wind, terrestial heat, atmospheric electricity, and sunlught. These last supply relatively unimportant parts of the world's total used energy, but all are renewable sources of energy. The supplies of elements suitable for nuclear reactions are finite but abundant.

The laws of motion and universal gravitation

2015-06-21T11:53:00.001-07:00

The laws of motion and universal gravitation

Newton's laws of motion.

Sir Isaac Newton (1642 - 1727), one of the most profound scientists of all time, interpreted and correlated many observatiorions in mechanics and combined the results into three fundamental laws, known as Newton's laws of motion.

First law of motion.

A body at rest remains at rest, and a boy in motion continues to move at constant speed along a straighr line, unless there is a resultant force actiong upon the body. The forst part of the law is evident from everyday experience; for instancem a book placed on a table remains at rest. The second part of the law is more difficult to visualize; it keeps on moving without the action of any further force. This statement is correct; the body would continue to move without any reduction of velocity if no force acted upon it.

Hower, expirience shows thet a retarding force is a always present in the nature of friction, If friction could be eliminated entirely, a body once set into motion on a level surface would continue to move indefinitely with undiminished velocity.

Therefore, uniform motion is a natural condition and maintains it self without the actionn of a resultant force, It is interesting to note that whether a body is at rest or moving with constant speed along a straight linem its acceleration is zero. Hence the first law of motion means that a body accelerates only while some resultent force acts upon it.

Second law of motion

The acceleration of body takes place in the direction of the resultant force acting upon it; the acceleration is directly proportional to the resultant force and inversley proportional to the mass of the body. Int general, the greater is the acceleration.

Third law of motion

For every action there is an equal and opposite reaction, and the two are directed along the same straight line. In this statement, the term "action" means the force that the second body exerts on the first. It should be noted that the action and reaction are never exerted on the same object. Thus, action and reaction, althouhg aqual and opposite, can never balance each other. Consequently, the first and second laws deal with forces on a single body; the third law deals with the mutual forces between two bodies.

Law of universal gravitation

Newton also showed that every particle in the universe attracts every other particle, and explained how this attraction is affected by masses of the particles and the distance separating them. The law reads: Each particle of matter attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Pull of gravity - weight

The most familiar illustration of universal gravitation is the force of attraction which the earth exerts upon objects near it, causing the objects is restrained so that it cannot fall when released, the earth exerts the same force on it, but the pull of the earth is balanced by some equal and opposite force exerted by the restraining agent.

The force of attraction that the earth exerts on a body, that is, the pull of gravity on it, is called the weight of the body. The weight of a body is a force and can be treated in exactly the same way as any other force. Its direction is, however, always toward the center of the earth.

The concept of momentum

Among the concepts of physics that have to do with force and motion, one of the most fundamental is momentum. The momentum of a body is defined as the product of its mass and its velocity. This concept prompts a further consideration of Newton's second law of motion. This law states that a body acted upon by some resultant force undergoes a change of momentum which is equal to the impulse of that force (impulse is the product of a force and the time during which it acts). The impulse has the same direction as the velocities.

The law of conservation of momentum is a pricinple which states that the total momentum of an isolated system stays constand regardless of any interactions that may take place among its parts. The law is one the great generalizations of physics.

Matter, force, motion, and friction

2015-06-21T10:10:00.001-07:00

Matter, force, motion, and friction

The concept of matter.

We know that physics began with the more or less qualitative passive observation of obvious natural phenomena, such as the downward motion of a freely falling body, the tides of the ocean, the lightning, the rainbow, the mysterious behaviour of magnets, etc. Very early there then came to be looked upon as properities of this basics, i .e., the thing called matter. Just what matter is, was never quite clear. Even today we cannot say with confidence what matter is, but we still talk about a great many physical phenomena as properities of matter, and with the greatly increased study of atomic structure we feel that we are some reaching gradually a clearer understanding of the constitution of matter.

The states or phases of matter.

It is customary to divide matter into three groups in accordance with the appearance it presents to the eye and the effect it has on the othes sensess. These groups are known as states or phases. At any given temperature, e.g. , that of the room (about 20°C), certain substances take the solid form, others are in the liquid phase, and still others are gaseous. We are all familiar with the general characteristics of these phases: how solids have a definite volume nad shape which are not readily changed save by the application of stresses, while a liquid takes the shape of the vessel in which it is placed, although its volume is definite and it possesses a free boundary surface, Finally, a gas takes both its volume and its shape from the contaning vessel and has no free surface.

Force and motion.

Acceleration is always produced by force.

Whenever a body is acceleratinh, a force is acting upon it to cause the acceleration. Thus, a force is aplied to a body to set in motion, A gain, a force is aplied to a body already in motion in other to speed it up, slow it down, or change its direction, Any change in velocity implies an acceleration, and this acceleration can be produces only by force.

A force can be described as a push or a pull acting on a body. Although a force must act upon a body when it accelerates, it does not necessarily follow that a body will accelerate whena force acts upon it. When all of the forces acting upon a body are taken into account and these do not balancem then the u alanced force is the resultant force acting on the body; this resultant always causes acceleration.

Motion of a rigid body.

We have learned that forcess applied to a body cause the body as a whole to accelerate in the directlion of the resultant force. Such motion, in which every particle of the body has the same velocity and the same acceleration, is called translation, But a torque acting upon a body may produce an entirely different kind of motion, in which the particles of the body describe concentric circles about a fixed line as an axis, a motion known as rotation. In generalm a body may undergo translation or rotation, or a combination of these motions, depending on how the forces are applied with respect to a particular point called the center of mass of the body.

Force and friction.

The surface of any solid if magnified sufficiently is found to be rugged and uneven, with minute hills at some places and valleys at others. If two surfaces are pressed together, these irregularities intermesh somewhat. Because of these surface irregularities, opposition is encountered to the sliding of one surface over another. This oposition, called sliding friction, incrrases as the contacting surfaces are pressed more firmly together. Experiments with metal surfaces in sliding contact indicate that increased pressure may result in high local temperatures at the contacting areas, followed by siezure, in which portions of the two surfaces become welded together, with the subsequent tearing away of relatively large particles. A frictionless or so-called smooth surface represents an ideal that is never attained on partice. Notwithstanding its disadvantages, friction has ceratin useful aspects; indeed, a person could not walk on the ground without friction.

Branches Of Engineering

2015-06-21T08:57:00.001-07:00

Branches Of Engineering

Engineering has been defined as the art of directing the great sources of power in nature for the use and convenience of man. In its modern form the practice of engineering involves men, money, materials, machines and energy. It is differentiated from science because it is primarily concerned with how to apply and direct to useful ends the basic natural phenomena which scientists discover and formulate into acceptable theories. It is always dissatisfied with present methods and equipment. It seeks newer, cheaper, better means of using natural sources of energy and materials to improve man's standard of living and to diminish laborius toil.

Traditional engineering.

Traditionally there were two divisions or disciplines, military engineering and civil engineering, As man's knowlendge of natural phenomena grew and the poteintial civil applications became more complex, the civilengineering discipline tended to became more and more specialized. The practicing engineer began to restrict his operations into narrower channels. For instance, civil engineering came to be concentrate on dymanic structures, such as machinery and enginees. Similarly, mining enginering became concerned with the discovery of and removal fromgeologocal structures of metall i ferous ore bodies,whereas metallurgical engineering involved extraction and rafinement of the metals from the ores. From the practical applications of electricity and chemistry, electrical and chemical engineer arose.

This fractionating process continued as narrower specialization became more prevalent. Civil engineers had more specialized training as structural engineers, dam engineers, wather-power engineersm bridge engineers; mechanical engineers as machinemachine-design engineers, industrical engineers, motive power engineers (and the latter into telegraph, telephone, radio, television, and radar engineers, whereas the power engineers divided into fossil-fuel and nuclear engineering); mining engineers into metallic-ore and fossil-fuel mining (the latter into coal and petroleum engineering).

Integrating influences.

While this specialization was taking place, there were also integrating influences in the engineering field. The growing complexity of modern technology called for many specialistic to cooperate in the design of industrial processes and even in the design of individual machines. This brought interdisciplinary activity to coordinate the specialists. For instance, the design of a modern structure involves not only the static structural members but a vast complex including moving parts (elevators, for example), electric machinery and power distribution, communication systems, heating, ventilating and air-conditioning, and fore protection. Even the structural members must be designed not only for for static loading but for dynamic loadings such as for wind pressures and eathquakes. Because men and money are as much involved in engineering as materials, machines, and energy sourcesm the managment engineer arose as another integrating factor in modern technology.