Research topics in physics pptx

KE = 1/2mv 2 Where: KE: kinetics energy in Joule m: mass in kg v: velocity in m/s Potential energy exists whenever an object which has mass has a position within a force field.. Heat

Physics

Physics has an important role in our life Without physics and the work of physicists, our modern life would not exist Using physics, people created machines, instruments and some different divices from the crudest to the most modern aspect Techology is developed more rapidly, more modern day by day

Moreover, all other natural sciences- example chemistry, biology, medicine- depend upon physics for the foundations of their knowledge Physics holds this key position because it is concerned with the most fundamental aspect of matter and energy and how they interact to make the physical universe

Physics has some main problems: mechanics, electricity and magnitism, heat, wave and sound, optics, nuclear physics, atomic particles

CHAPTER 1: MECHANICS

Mechanics is a branch of physics concerned with the behavior of physical bodies under the effect of the bodies on their enviroment The early modern period, scientists, such as Galileo, Kepler and especially Issac Newton, laid the foundation for a field of mechanics and now it is known as classical mechanics or Newtonian mechanics

Mechanics has two major divisions: classical and quantum mechanics

Classical mechanics came first while quantum mechanics did not appear until 1900 Both commonly constitute the most certain knowledge that exists about physical nature

Classical mechanics is concerned with the physical laws governing the motions

of bodies It is used for describing the motion of marcroscopic objects, such as: parts

of machinery, astronomical objects inclue spacecraft, planets, stars, galaxies It is one

of the oldest and lagest subjects in science, engineering and technology

Classical mechanics is divided into: statics, dynamics and kinematics Statics studies matter at rest or in motion with constant velocity It deals with the balancing

of forces with approriate resistance to keep matter at rest It is commonly used for designing buildings and bridges Different from statics, dynamics studies matter in motion, example motion of stars, baseballs, gyroscopes of the water pumped, and even air plane Kinematics studies motion without regard to the forces present It is simply a mathematical way to describe motion

Three Newton’s laws:

Classical mechanics is governed by three basic principles, which were first formulated in the 17th and 18th centuries by Isaac Newton These principles are

known as Newton’s laws

The first law describes a fudamental property of matter, and often called the

“Law of Inertia”, as follows: Every object in a state of uniform motion tends to

remain in that state of motion unless an external force is applied to it The key point here is that if there is no net force acting on an object (if all the external forces cancel

each other out), the object will maintain a constant velocity, if that velocity is zero, the object remains at rest and if having an external force to apply, the velocity will change

Newton’s second law describes the manner in which a force compel a change

of motion, at a rate of change called acceleration It can be state as follows:

F=ma

Where

F: the applied force

m:mass of the object

a: the object’s accerleration

Acceleration and force are vectors, in this law the direction of the force vector

is the same as the direction of the acceleration vector

This law allows quantitative canculations: how do velocity change when forces are applied Notice the fundamental difference between Newton’s 2nd law and the dynamics of Aristotle: according to Aristotle there is only velocity if there is a force, but according to Newton an object with certain velocity maintains that velocity unless the force acts on it to cause an acceleration

Newton’s third law can be stated as follows: For every action in nature there is

an equal and opposite reaction In other words: if object A exerts a force on object B, then object B also exerts an equal force on object A Notice that the forces are exerted

on different objects

This law explains what happens if we step off a boat onto the bank of a lake: as

we move in a direction, the boat tends to move in the opposite direction

Mass, force and acceleration

Mass is the amount of matter in a body The mass of a body remains constant

In the metric system mass is measured in kilogram (kg) Sometimes we use weight,

or the pull of gravity upon matter The object’s weight depends on the gravitational pull acting on it An object’s weight is much less on the moon than it is on the Earth, and in outer space a body’s weight may be nearly zero

When an object’s velocity changes, it accelerates Acceleration shows the change in velocity of a body in a unit time According to Newton’s 2nd law, it is direct result of the applied force In the metric system, acceleration’s unit is (m/s)/s

When we study mechanics, we can know a concept: force Force is a vector quantity that has both a specific magnitude ( size or length) and direction It is

characteristic for a body’s acting to other It changes the motion of a free body or cause stress in a fixed body It can also be described by concepts such as a push or pull that can cause an object with mass to change its velocity, to accelerate, to

deform

If two forces applied simultaneously to the same point have the same effect as

a single equivalent force, called resultant force We can canculate the net force:

F=F1+F2+…

If two forces acting on an object is the same direction (parallel vectors), the

resultant force is equal to F1+F2, in the direction that both two forces If two forces

acting on a object is opposite directions, the net force is equal to |F1-F2 |, and

direction of whichever one has greater magnitude If the angle between the forces is anythingelse, the net force must be added up using the parallelogram rule

The same forces can have different effects depending on applied way and applied body A force may cause a body to spin or rotate if applying in a certain way The tedency of a force to rotate the body is known as torque, it is also a vector

quantity Its magnitude can be calculated by multiplying applied force to the distance between the line of force and the axis of rotation

A kind of force which resists the motion of a body along a path is friction It appears only when other forces are applied or if a body is already in motion It may

be undersirable in some cases, example: air resistance that slows down an airplane, but in some other cases, it is useful, example: car brakes

Center of gravity and equilibrium :

It’s difficult to apply the laws of mechanics to a particular body The problem

is more simple if we study the behavior of an object’s center of gravity instead of studying the behavior of entire pbject The center of gravity is a point at which the weight of a solid object can be considered to be concentrated all forces appear to act upon this center If the line of exerted force does not pass through the center of

gravity, a torque is created

A body can be completely at rest if all forces and all torques are balanced A complete balance exists If the sum of all forces and torques acting on a body is equal zero, we say that the body is in equilibrium

A body in equilibrium may be in one of three states: stable, unstable, neutral equilibrium When a torque apply to a body, after the torque ceases to act, if the body tends to return to its original position, it is in stable equilibrium If it continues to turn

to a new position, it is known as unstable equilibrium The body is in neutral

equilibrium if it comes to rest wherever it may be when the torque is removed

Work, energy and power

Work: when a force makes a body move, the product of the force times the distance through which the force acts is called the work done by the force There are some example of work which we can observe in everyday life: a horse pulling a plow through the field, a man pushing a cart, a weightlifter lifting e barbell above his head, etc Mathematically, work can be canculated by the following formula:

A=F d cosα

Where

F: the force ( in Newton)

d: the distance through which the force acts (the displacement), (in meters)

α : the angle between the force and the displacement vector

Energy is the capacity for doing work If work is done on a body, the energy of the body increases Energy is consists of kinetic and potential energy Energy

associated with motion is kinetic energy It is equal to one half the product of its mass times the squre of its velocity represented by a formula:

KE = (1/2)mv 2

Where:

KE: kinetics energy (in Joule) m: mass ( in kg)

v: velocity (in m/s)

Potential energy exists whenever an object which has mass has a position within a force field The most everyday example of this is the position of objects in the earth’s gravitational field In this case, the potential energy of an object is given by:

PE = mgh

Where: PE: potential energy ( in Joules)

m: mass ( in kg) g: gravitational acceleration of the earth ( 9.8 m/s/s) h: height above earth’s surface ( in m)

Conservation of energy

This principle asserts that in a closed system energy is conserved This

principle will be tested by the experiment in the case of an object in free fall When

the object is at rest at height h, all of its energy is PE As the object falls and

accelerates due to the earth’s gravity, PE is converted into KE When the object strikes the ground, h=0, so that PE=0, the all of the energy has to be in the form of

KE and the object reaches the maximum velocity In this case we are ignoring air

resistance

Power is the rate of doing work or the rate of using energy Unit of power is watt If we do 100 joules of work in one second ( using 100 joules of energy), the power is 100 watts

Some simple machines

Many principles of mechanics are clearly demonstrted in devides called simple machines These machines have been known since antiquity with crude machines or now with modern machines They are the lever, the wheel and axle, the inclined plane, the screw, the rope-and-pulley system They are designed to amplify the effect

of forces or to do work to move weight or to overcome resistances

Chapter 2: Heat

Definition and applications

All living things need heat Heat is a form of energy transferred from one object to another caused by a different in temperature between these objects Some other words:

- Heat is defined as energy in transit from a high-temperature object to a lower one

- Heat is a form of energy possessed by a substance by virtue of the vibrational movement of its molecules or atoms

- Heat is the transfer of energy between substance of different temperatures Heat has an important role in our life It causes natural changes which occur in

an endless cycle To explain some phenomena in the nature, we can use concept of heat Example the atmosphere in tropical areas is hotter than it in polar areas because tropical areas receive more heat from sun

The amount of heat from the sun that falls on the region determines the

temperature range of the region The temperature of environment effect to plant, animal and even man Heat is a very important factor in making our life and our world

The nature of heat

Despite having many definitions of heat, heat has one nature We can know heat when we were a child We could detect it easily through its effect: burning But

do you know what heat itself actually is? Heat cannot be weighed and cannot be seen

or heard too

To understand the nature of heat, we may study its acting, we can use the kinetic theory of matter According to this theory, all matter made of atoms and molecules in constant motion When matter absorbs energy, the random internal energy and the motion of these atoms and molecules are increased This increase makes itself in the form of heat, and when it occurs, the temperature of the matter rises This leads a conclusion: when the energy of motion has been transferred to the random motion of the atoms that make up the matter, the motion of the atoms is speeded up and heat is produced That is the nature of heat

Sources of heat

Heat is very necessary for life, so it is important to know where it comes from and how it can be used The most important source of heat for our Earth is the

radiation from the sun The Earth absorbs a part of heat from the sun This keeps the temperature of the Earth’s surface and atmosphere at a level which permits life to continue

The second important source of heat is the store of natural fuel on and in the Earth, such as: coal, oil, gas, wood They do not provide heat constantly and

automatically as the sun does They are composed of carbon, hydrogen, and other elements In a certain temperature, the combustion occurs, the fuels react chemically with oxygen This reaction releases a large quantity of heat

The definition of specific heat

The specific heat is the amount of energy that is transferred to or from one unit

of mass or mole pf a substance to change its temperature by one degree Specific heat

is a property, it depends on the substance under consideration and its state

The temperature

Temperature is the property that gives physical meaning to the concept of heat And object has low temperature if it is cold, and vise versa When contacting with a

cold body, a hot body gives up some of its heat to the cold one The process will continue until both have the same temperature

Definition of temperature is based on some constant value, absolute zero

Absolute zero is defined as the temperature at which all molecules and atoms’ motion stops completely It is equal to -273.16 Celsius or 0 Kelvin We can define

temperature as: temperature of a substance is a measure of the intensity of motion of all atoms and molecules in that substance

To measure temperature, we use the themometer scale Its working is based on the fixed points of boiling water and freezing water There are four scales:

Fahrenheit, Celsius, Kelvin, Rankine We can change from this scales to different one Some useful conversation relation:

Fahrenheit to Celsius: T(C)=5/9(T(F)-32) Celsius to Fahrenheit: T(F)=9/5 (T(C)+32) Celsius to Kelvin: T(K)=T(C) + 273

Fahrenheit to Rankine: T(R)=T(F)+460

Kinetic Theory

Heat is not a material fluid It is the result of a conversion of energy It is a form of energy It is equivalent to mechanical energy We have a conversation: one calorie of heat energy is equal 4.184 joules of mechanical energy In an isolated system, work can be converted into heat at ratio of one to one

Three laws of thermodynamics:

The zeroth law: Energy can be only transferred by heat between objects (or areas within an object) with different temperature

The first law: in an insolated system, work can be converted into heat at ratio

of one to one

The second law: Heat transfer happens spontaneously only in the direction from the hotter body to the colder one

The Transfer Of Heat

Heat transfer helps to shape our world Heat always travels or flows from a high temperature to a low temperature In the nature, there are three different methods

of transfer heat They are: radiation, conduction, and convection

Radiation

Radiation is a process of transferring heat energy from one place to another This process occurs when the internal energy of a system is converted into radiant energy at a source such as heater This energy is transmitted by invisible wave

through space Example the sun radiate heat outwards through the solar system

Finally the radiant energy touch a body where it is absorbed and converted to internal energy And then heat appears By radiation, heat only travels in space or in gases All bodies, whether hot or cold, radiate energy The hotter a body is, the more energy it radiates A body at constant temperature radiate energy continously It is receiving energy at the same rate that is radiating energy So it doesn’t change in internal energy or temperature

Radiation transfer depends upon the shape of the radiating object It is not proportional to the difference in temperature between two object but it is proportional

to the fourth powers of the absolute temperature

Conduction

Conduction is the most significant means of heat transfer in a solid If one part

of a body is heated by direct contact with a source of heat, the next parts become heated This may be explained by the kinetic theory of matter When the temperature increases, heat motion of molecules raises, this violent motion passes along the body from this molecule to another and result: the body is heated and this process is known

as conduction Example, if dipping simultanously a silver and a wood spoon into boiling water, the handle of the silver one rapidly becomes hot while the wood one still is cool

Materials in which heat transfer happens easily and quickly are known as good conductors, example all metals In meterials such as wood, rubber and air, heat is not transferred readily from one molecule to the next, they are called insulators

Conduction occurs readily in good conductors of heat Conduction depends upon the different of temperature and the resistance of the flow of heat The greater the

temperature difference between two point is, the more the driving force to move heat

is The less resistance is, the easier heat transfer is

Convection

The third method of heat transfer is covection It happens in liquids or gases (commomly called fluids) Convection occurs when having the change of density (mass per unit volume) If heating fluid, its density decreases, so it becomes lighter The part of warmer fluid will rise while the part of colder will decend This process happens continously until having balance in temperature Some examples in the fact: water in a kettle is heated by convection; the air in the room is heated by convection when putting a stove in that room; or when we drop a few crystals of potassium permanganate into water, we can see movement of pink water, convection occurs

Chapter 3: Electricity

Electricity is a general term heat emcompasses a variety of phenomena

resulting from the presence and flow of electric charge These inclue many easily recognizable phenomena, such as lightning and static electricity

In general usage, electricity refers to a number of physical effects However, in scientific usage, it inclues these related concepts: eletric charge, electric current, electric field, electric potential difference, electromagnetism

Electrical phenomena have been studied since antiquity Until the 17th and 18th centuries, advances in the science were not made And until the late 19th century, engineers were able to put it to industrial and residential use The rapid expansion in electrical technology at this time transformed industry and society Electricity almost has no limits, it can go anywhere, even far into space It has applications in transport, heating, lighting, communications and computation We cannot imagine today’s world without it Electricity keeps an important role in our world

Electric Charge

Electric charge is a property of subatomic particles, it determines those

particles’ electromagnetic interactions Charge originates in the atom Atoms cotains two kinds of charge: negatively charged electrons and positively charged protons In

an isolated system, charge is a conserved quantity Within the system, charge may be transferred between bodies following two ways: direct contact or passing along

conducting material The informal term static electricity refers to the net presence of charge on a body, usually caused when rubbing dissimilar together, transferring charge from one to another

A light-weight ball suspended from a string can be charged by touching it with

a glass rod that has been charged by rubbing with a cloth If a similar ball is charged

by the same glass rod, two balls will repel each other They also repel each other if they are charged by rubbing with an amber rod, and the other by an amber rod, two ball attract each other These phenomena were investigated in the late 18th century by Charles Augustin de Coulomb He discovered the well-known conclusion: like

charges repel and unlike charges attract each other He gave a law to show the

relationship between amount of electric force that two charged objects exert upon each other and the distance separating them, called Coulomb’s law This law is stated

by the formula:

Where: r: the distance between two charges

k: a constant for converting units of charge and the distance into units of

force

q1,q2: charges of two objects

The charge on electrons and protons is opposite in sign The mount of charge is usually given the symbol q, and its unit is coulombs (C) Each electron carries the same charge, about -1.6022.10^-19 (COP TREN MANG NHE), and the proton is +1.6022…

In a atom, if numbers of protons and electrons are equal, the atom is neutral If

a neutral loses electrons, it has an excess number of protons and it is positively

charged If a neutral atom gains electrons, it has an excess number of electrons and it becomes negatively charged

Electric Current

An electric current is the movement of electric charge This moving charge may be electrons, protons, ions, even positive “hole” in semiconductors We calculate the current by the formula:

Where

Q: the total charge ( in coulombs)

t: the time (in seconds)

The current I is measured in amperes A one-ampere current means that one

coulombs of electric charge passes each point in the circuit each second Addition to coventional current has been described as the direction of positive charge motion

Electric Field

The concept of electric field was introduced by Michael Faraday in the 19th century Electric field is space that surrounds a charged object and exerts a force on any other charges placed within the field We all know that charged object can exert forces on uncharged objects over a distance We use the electric field to describe possible effects at a point in space about an electric charge An electric field generally varies in space, its strength at a point E is defined as:

E=F/q

Where

F: the electric force on a test charge

q: the size of the test charge placed at that point

The electric field strength is a vector quantity, having both magnitude and direction Specifically it is a vector field

The study of electric field created by stationary charges is called electrostatics The field may be visualized by a set of imaginary lines These lines give an overview

of the electric field, their direction at any point is the same as that of the field These lines are called “lines of force” This concept was introduced by Michael Faraday The field lines are the parths that a point positive charge would to seek to make as it was forced to move within the field They have key properties:

- They originate at positive charges and end at negative charges

- They must enter any good conductor at right angles

- They may never cross nor close in an themselves

Electric Potential

Placing a positive test charge near a fixed positive point charge, it will

accelerate away and increase in velocity and klinetic energy But to move this

positive test charge back toward the fixed positive charge, we must do a work on the test charge The energy put into this process is stored as electric potential energy The electric potential at any point is the energy required to bring a unit test charge from

an infinite distance slowly to that point It is measureed in volts, one volt is the

potential for which one joule of work must be done to bring a charge of one coulomb from infinity In the fact, we don’t often use this concept A more useful concept is that of electric porential difference It is a measure of this change in energy as the charge moves from one place to another in an electric field It is given by defining energy change to charge moved Its unit is volt Sometimes it called voltage When the voltage is zero ( or electrical potential between points in a field is not different), electric charge does not move between those points When potential different

between two points in a field is large, positive electric charge will tend to move from higher to lower potential and negative charge will move the opposite way

Electromagnetism

In 1821, the Danish scientist Han Christian Oersted discovered magnetic field that existed around all sides of a wire carrying an electric current If bringing a

compass near a current carrying wire, its magnetized needle would realign If the current is reversed in direction, the compass needle reverse its orientation A

magnetic field is created arround the current-carrying wire We can represent this magnetic field as a series of concentric field lines in planes perpendicular to the current, called the magnetic field lines When the direction of current is known, we can use the right-hand rule to find the field direction That rule can be stated as: put the right hand with the thumb pointing in the direction of current and the finger encircles the wire, the magnetic field lines are the same direction as the fingers Or

we can predict the field direction by using a magnet: the direction of the magnetic field is from north to south pole of magnet

Magnetism and electricity have a direct relationship A current exerts a force

on a magnet and a magnetic field exerts a force on a current Magnetism is induced

by an electric current is known as electromagnetism and the field which it works is callled electromagnetic field

Ampere investigated the relationship between electricity and magnetism And

he discovered that two parallel current carrying wires exerted a force upon each other: two current in the same direction attract each other, and vise versa, currents in positive direction repel each other

Electric Circuit

A basic circuit can be described as: the voltage source, example battery, is

connected with a resistor R through wires, a current I from the source transfer

through the resistor, and from the resistor, the current returns to the source An

electric circuit is produced If the source is the a battery, between the terminals of the battery there is a potential difference, under acting this potential, electrons flow in one direction, away from the negative terminal toward the positive The current has a direct relationship to the voltage of the battery, and it depends on the nature of the conductor This relationship is shown in Ohm’s law which was stated in the 19th century by Georg Simon Ohm This law is given by a formula:

U = IR

Where

I : the current ( in amperes)

U : the potential difference (in volts)

R : the resistance (in ohms)

Chapter 3: Optics

Optics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it Optics usually describes the behavior of visible, ultraviolet, and infrared light

Most optical phenomena can be accounted for using the classical

electromagnetic description of light However complete electromagnetic descriptions

of light are often difficult to apply in practice Practical optics is usually done using