easa part 66 m2 physics short notes by lhkhattak
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Module-2 Short Notes
Lal Hakim Khattak Aviation Maintenance Training College
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Module 2 Physics EASA PART 66
Basic SI Units Length (L) Metre (m) Mass (m) Kilogram(kg) Time (t) Second (s)
Derived SI Units Area (A) Square Metre (m2) Volume (V) Cubic Metre (m3) Density ( ) Kg / Cubic Metreρ
(kg/m3) Velocity (V) Metre per second (m/s) Force (F) Newton (N) Pressure(p) Pascal (Pa) Energy (E) Joule (J) Work (W) Joule (J) Power (P) Watt (w) Frequency(f) Hertz (Hz)
Matter anything that occupies space. consists of atoms and molecules. • Atom
smallest particle in an element that has the properties of the element.• Molecules the
combination of two or more atoms.
Nature of Matter• Nucleus each carrying a positive charge are called protons.
In addition to the protons the nucleus usually contains electrically neutral particles called neutrons.
Neutrons have the same mass as protons whereas electrons are very much smaller Neutron simply adds
to the weight of the nucleus. has no charge.
Proton positively charged. has mass same as the neutrons.
Electron orbits define the size or volume occupied by the atom negatively charged. total number of negatively
charged electrons matches number of positively charged protons. Atomic Number – no. of protons in the atom’s
nucleus•
Mass Number – total no. of protons and neutrons in nucleus.
Isotopes• are atoms that have same atomic number but different mass numbers.
Atom gains / loses one or more neutrons from nucleus will become ISOTOPES.
Chemical Compounds • Atoms bond together to form a molecule. Molecules Monatomic Molecule Chemical Compounds Consists of single type of atom. Made up of two or more atoms. Structure of Atoms• Electrons are arranged in energy levels and shells around the nucleus and with increasing distance from the nucleus.
Valence electrons : how many electrons an atom has in its outer shell. determines the chemical behavior. The
more valence electrons, the more want for the atom to get more electrons •
Valency :1. bonding capacity of an atom; usually equals the number of unpaired electrons in the atoms outermost
shell.2. No. of bonds it can make with a monovalent atom such as Hydrogen. Monovalent Bivalent Trivalent
Tetravalent.
The Molecule• A group of two or more similar or dissimilar atoms bonded together •
Metallic bonds metal + metal (eg: Alloy).
Ionic bonds metal + nonmetal (eg: sodium chloride) •
Covalent bonds nonmetal + nonmetal (eg: water) produce molecules, strongest bond.
Chemical compounds: A substance made up of different elements that are chemically bonded and are so united that
the whole has properties of its own, which are unlike those of its constituents.
All other molecules made up of two or more atoms are known as Chemical compound.
States of matter• All matter exists in one of three physical states. • Physical state refers to the condition of a
compound and has no effect on a compounds chemical structure.
Solid. A solid has definite mass, volume and shape•
Liquid. A liquid has definite mass and volume but takes the shape of its container• Gas. A gas
has definite mass but takes the volume and shape of its container.
Increase in the temperature will increase the energy of its molecules.
Solid to Liquid – Fusion. Heat energy required to complete process of converting unit mass of substance from solid
to liquid state without change of temperature is called the Latent Heat of Fusion. Liquid to Gas – Vaporization. Heat energy required to vaporize a unit mass of liquid without temperature rise is
called Latent Heat of Vaporization. •
Gas to Liquid – Condensation. Heat energy expelled is called the Latent Heat of Condensation. Liquid to Solid – Solidification Loss of molecular energy is the Latent Heat of Solidification. Sublimation. Some solid substance when heated do not melt, but form a Vapor Solid
to vapor, without passing through liquid state.E.g. Dry ice• Evaporation Liquid change
to vapor. Some liquid has low boiling point, so easily change from liquid to vapor. e.g. Methylated spirits. Mechanics : Statics ; forces center of gravity stress and strain properties of matter pressure and buoyancy in liquids Newton’s
First Law of Motion A body at rest will remain at rest unless given an external force, or a body which is moving will
keep on moving unless given an external force. (Inertia ) Second Law of Motion A force proportional to the rate of change of its velocity is produced whenever a body (or mass)
is accelerated. F = ma Third Law of Motion for every action, there is an equal and opposite direction. Mechanics Static Forces• If a Force is applied to a body it will cause that body to move in the direction of the applied
force• Force has both magnitude (size) and direction. Forces cannot be directly observed, only their effects can be seen. Compressive force applied on an object to squeeze it. Tensile pair of forces try to extend an object. Shear Pair of forces tries to cause one face of material to slide relative to an adjacent face• Statics is used
to describe study of bodies at rest when forces are balanced.
External force force applied to an object from outside its boundaries. Internal force force induced in the object to react against externally applied force.
VECTOR AND SCALAR• Scalar – just a magnitude, there is no direction associated. eg. Time, mass, volume. Vector – require both magnitude and direction to be fully defined. eg. Force, velocity, acceleration. Adding Forces•
2 or more forces act at same line, produce resultant force. • If at straight line, subtract or addition. • Forces do not act
in a straight line – use the ‘parallelogram law’. Worked example Find the resultant of two forces of 4.0 N and 5.0 N acting at an angle of 45degree to each other. Using a scale of 1.0 cm = 1.0 N, draw parallelogram ABCD with AB = 5.0 cm,AC = 4.0 N and angle CAB = 45 degree,
MOMENTS AND COUPLES • If a body free to rotate about some point ;i. Applied force will cause rotation. Force
required dependent on how far from hinge force is applied. Turning effect = magnitude and distance. Momen t = force x distance. • In SI units, Newtons meters = Newton x metres
The Principle of Moments ‘If a body is at rest under the action of several forces, the sum of the clockwise moments
about any axis is equal to the sum of the anticlockwise moments about the same axis
IN EQUILIBRIUM• COUPLE – WHEN TWO EQUAL BUT OPPOSITE DIRECTION, CAUSES ROTATION
CENTRE OF GRAVITY • Gravity is a force which is always present and is a pulling force in the direction of the center
of the earth. • This force acts on every body through an imaginary point called the center of gravity (C of G).
A point where all the weight of a body appears to be concentrated. (total weight can be considered to act through
that datum position)
Stability / balancing• The lower the C of G, the stable an object is• The wider the base, the more stable an object is
– C of G towards the base.
The location of the center of gravity in the human body varies slightly, depending on body shape• a male with a
muscular upper body and small hips, the center of gravity is higher than in a female with narrow shoulders and wide
hips• in an infant with a large head in relation to its body, it is higher than in an adult
Stress • If force is exerted on a body, there will be mechanical pressure acting on the body which is called the stress.
Stress = *units: Newton meter 2, Nm2•
Components will fail due to overstressed, not overloaded.
Forces applied to the body will cause distortion of the body and change to the material’s crosssectional area; eg.
Tensile Forces will cause elongation Compressive Force will cause reduction in dimension.
There are 5 types of stress in mechanical bodies i. Tension ii. Compression iii. Torsion iv. Bending v.
Shear.
Tension • force that tends to pull an object apart
Compression• resistance to an external force that tries to push an object together.
Torsion• Torsional stress is applied to a material when it is twisted. •Torsion is actually a combination of both tension
and compression.
Bending• In flight, the force of lift tries to bend an aircraft’s wing upward.
Shear• combines tension and compression is the shear stress, which tries to slide an object apart.
Strain If the outside force is great enough to cause the object to change its shape or size, the object is not only under
stress, but is also strained. • If a length of elastic is pulled, it stretches. If the pull is increases, it stretches more; if the pull is reduced, it contracts.
Hooke’s law states that the amount of stretch (elongation) is proportional to the applied force. Strain =
change in dimension / original dimension ( No units )
Shear strain – straight motion. Torsion strain – rotational motion.
Shear strain Torsion strain• when the applied load causes • form of shear stress resulting one layer of material to move from a twisting action. relative to the adjacent layers Twist will be proportional to the applied torque.
Properties of matter Diffusion• Is the spreading of a substance of its accord. • due to molecular action, e.g. a smell,
whether pleasant or not, travels quickly from its source to your nostrils where it is detected. • occurs in liquids and
gases but not in solids.
Surface Tension• This suggests that the surface of a liquid behaves as if it is covered with an elastic skin that is trying
to shrink. • The surface tension can be reduced if the liquid is ‘contaminated’, adding a detergent to the water will
cause our needle to sink.
In a liquid, the molecules still partially bond together and prevents liquid from spreading nag expanding out.
Adhesion Force of attraction between molecules of different substances.
Cohesion Force of attraction between molecules of same substances.
Mechanical properties of Strength Matter A strong material require a strong force to break it Stiffness A stiff material
resists forces which try to change its shape or size.
Elasticity The ability to recover to its original shape and size after the force deforming it has been reformed Ductility
Materials that can be rolled into sheets, drawn into wires or worked into other useful shapes, without breaking are
ductile
Brittleness A material that is fragile and breaks easily
Pressure and buoyancy in• liquid The equivalent term associated with fluids is pressure: pressure = force / area or p
= F/A.
Pressure is the internal reaction or resistance to that external force.
Pascal’s Law: “pressure acts equally and in all directions throughout that fluid.”
Pressure can be transmitted to some other point in order to generate another force.
Units of pressure SI system pressure Pascal = force per unit area (Nm2)
Atmospheric pressure: Milibars (mb ) or pounds per square inch ( psi )Sea level standard atm pressure : 10132 mb
or 14.69 psi ( at 0C)
Buoyancy Archimedes’ Principle states that when an object is submerged in a liquid, the object displaces a volume of liquid equal to its volume and is supported by a force equal to the weight of the liquid displaced.
The body will floatif the buoyancy is positive
The body will sinkif the buoyancy is negative
The body will be stuckif the buoyancy is neutral
Linear motion• Is the uniform motion in a straight line• Motion is the change of position of a body with reference to another body. speed•
Speed tells us how quickly an object is moving at any given point in time• Average speed – dividing the distance travelled by the time taken Speed = rate of change of displacement or position = v = where v represents speed. Worked example• An aircraft flies at 80 km/ hr for 15 minutes and at 120 km/hr for a further 15 minutes. How far has it travelled and what is the average speed? velocity• Includes direction, distance in straight line and time• Acceleration• Is the rate of change of velocity over time. • If the rate of change is constant, acceleration is described
as being uniform. Acceleration If the velocity of an object increases over time. • Deceleration /
retardation – If the velocity decreases over time. Free falling objects• if a stationary object is released and free falls under attraction of the force of gravity, it will
accelerate at 9.81 m/s 2• So the ‘a’ will be 9.81 m/s 2 , but in this case it is given the symbol ‘g’.• If the object is
thrown upwards, its g will be – 9.81m/s2
Initial velocity of objects free falling from rest is zero, so the equations for free fall are: V = gt S = ½ gt2 V2 = (2gs)2
ROTATIONAL MOTION Circular Motion• Rotational motion means motion involving curved paths and therefore
change of direction. Centripetal Force• Continuous force applied to a body moving in circular path to keep it in that particular circular
path, preventing it from travelling in straight line (tangential to circle it is rotating in) – due to the inertia of the object. Basically a force acting inwards toward the center of the circle. • Is directly proportional to the mass of the object in
circular motion. • Is inversely proportional to the radius of the circle in which the object travels. Force = ma, so we
can say that the object has an inwards acceleration called Centripetal Acceleration Centrifugal Force• Is the equal but
opposite reaction to the Centripetal Force. (Newton’s 3rd Law) Tensile Force at the other end of the string acts
outwards of the circle.
Periodic motion• Some masses move from one point to another, then back to the original point, and continue to do
this repetitive The time during which the mass moved away from, and then returned to its original position is known as the time period, and the motion is known as periodic motion• Example: pendulum Pendulum• When the mass then displaced from its rest position, it will accelerate back towards its rest position. • On
reaching it however, it will not stop, because its inertia carries it on to an equal but opposite displacement. • the time
period can be measured from a any position, through to the next time that position is reached, with the motion in the
original direction. Cycle –for one complete to and fro movement Periodic Time – time taken to complete 1 cycle. Frequency – the number of cycle occurring in 1 seconds. (Hertz – HZ ) Amplitude – maximum displacement of a body from its middle or rest position. Periodic time, T can be calculated by; T = 2 √ (L / g) Where; L – length of the pendulum g – magnitude of acceleration due to gravity = 9.81 m/s2 For time period ( T ) and frequency ( f ) ; Resonance• When force subjected to force vibration, it will vibrate along with natural frequency of the object. • If the
natural frequency matches the resonant frequency with forced vibration causes the amplitude to increase
dramatically. • Natural frequency tries to damped out the amplitude but cannot damp its own natural frequency. • So
the two amplitudes combine to produce resonance.
Machine – utilize some form of motion to convert an applied force into a useful work output• The input forces is often
amplified many times by the machine so that we can overcome a heavy load with little effort. • e.g.; levers, pulleys, gears, screws.
Velocity ratio• Ratio of distance the effort is required to move in comparison with the distance the load moves in the
same time. Velocity Ratio = Distance moved by effort /Distance moved by load Mechanical Advantage • Describes the ratio of load moved with the effort required to move it. Mechanical
Advantage = Load Effort *A rusty car jack will have a low mechanical advantage because much of the effort would be used to overcome the friction of a corroded screw thread. Efficiency • Describes the ratio of the useful work done by a machine to the total work put into it. Efficiency = Work
Output x 100% or Mechanical Advantage x100% Work Input Velocity Ratio• Expressed as percentage and is always
less than 100%. *Friction and slippage can detract from efficiency of a machine. Levers • Used to gain mechanical advantage• Most basic form. seesaw that has weight at each end. (weight on one
end tends to rotate it clockwise, weight on the other end tends to rotate it anticlockwise) First Class Lever• Lever has
fulcrum between load and effort• Less effort required to lift the load. Second Class Lever• Has fulcrum at one end of the lever and effort is applied to the opposite force. Third Class Lever• Force is applied between fulcrum and load.• Pulleys• Pulley wheel has circumferential groove to accept a rope.• Effort is applied by pulling on a rope.• Tension
created in the rope and movement are transmitted through arrangement to the load.• Single fixed pulley is a
convenient means of lifting a light load.• So, for instance, if one end of the rope is attached to a fixed object, pulling
on the other end will apply a doubled force to any object attached to the axle.
Mass• Is the quantity of matter that it contains. • Constant regardless of its location.• Basic SI unit : kilogram (kg)•
Imperial : pounds (lbs) Weight Force with which gravity attracts a body• Varies with distance between body and center of the earth, so if
farther than centre of the earth, the less it weighs.• So, it is said that an object in deep space does not has no weight,
but do has mass.
Gravitational acceleration is considered as 9.81m/s2. Force• Is a vector quantity that has magnitude, direction and a point of application.• Which changes a body’s state of
rest or of uniform motion.
Newton’s First Law• A body at rest will stay at rest unless given an external force, or a moving body will continue on
moving unless given and external force•
Inertia Is the resistance to movement or changes. Work is done when a force move. Work done = force x distance moved in the direction of the force•Unit : Newton metre (Nm) or the joule 1 joule the work done when a force of 1 Newton is applied through a distance of 1 metre
Power• The amount of work done in specific time.
Power = work done = force x distance time taken time• Si unit : Watt ( W ) – 1 Joule/ second• Is the rate of work done
when 1 Joule is achieved in one second.*One horsepower is the equivalent of 746 Watts. Brake Horse Power• To
rate the engine power• The engine is made to do work on a device known as dynamometer or ‘brake’ – loads the
engine output.
Shaft Horse Power• Measure output shaft of a turboprop engine, since the power produced at shaft is what will be
delivered to propeller.
Energy• Is the capacity to do work• Si unit: Joules• Can appear as several form But only deal with Mechanical Energy,
and appears as potential and kinetic energy•
Energy will not be converted into 100% work; they will always appear in a less useful form such as wasted heat• But it may be converted into 100% energy.
Potential Energy (PE)• Energy is possessing by virtue of its position or state• Potential Energy = mass x gravity x height = mgh Kinetic Energy• Energy it possesses by virtue of its motion• Kinetic Energy = ½ mv2
Conservation of Energy “Whenever energy is converted from one form to another, none of it is lost. Efficiency =
work output work input*usually expressed as percentage (less than 100 %).
Heat• Defined as energy between two bodies because of difference in temperature•
Momentum• Product of its mass and velocity. Momentum = mass x velocity• SI unit ; kgm/s
Impulse of a force• If a body was subjected to a sudden blow, shock load or impact, it will be possible to measure change in momentum• Forces which have the short time duration are called the Impulsive forces•
Change of momentum due to impulsive force is called the Impulse• Impact duration small – impulsive force large. Impact duration large – impulsive force small.
Impulse• Product of force and time or change in momentum• Impulse = change in momentum = mass x change in velocity. = force ( N ) x time ( seconds )
CONSERVATION OF MOMENTUM “When two or more masses act on each other, the total momentum of the masses
remains constant, provided no external force, such as friction, act.”
CONSERVATION OF MOMENTUM MOTION MOMENTUM First law First Law Mass remains at rest or continue to move at constant velocity, unless acted move at constant velocity, unless acted on by an external force. on by an external force.
Second Law Second Law F = ma Rate of change of momentum is proportional to the applied force Third Law Third
Law For every action, there is an equal and If mass A exerts force on B, then B exerts opposite reaction. an equal but opposite force on A. The rate of change of momentum is proportional to magnitude of force causing it.• When two bodies, one of low mass and the other of high mass, are acted upon by the same force for the same time, the low body mass will build up higher velocity than the heavy mass. Example: A moving snooker balls, each ball has its own momentum before collision. After collision, the sum of the two balls’ momentum will be the same as the sum prior to the collision even though their velocities may have changed.
sum of momentums of balls = sum of momentum after impact prior to impact mu1 + mu2 = mv1 + mv2
Moment of inertia• considers the effect of mass on bodies whose moment is rotational Moment of inertia is a function of mass and radius•
GYROSCOPES• is a rotor having freedom of motion in one or more planes at right angles to the plane of rotation• With the rotor spinning, the gyroscope will possess two fundamental properties: Gyroscopic rigidity or inertia Gyroscopic precession.
Gyroscopic rigidity• maintains the axis of rotation constant in space• if a gyroscope is spinning in free space and is
not acted upon by any outside influence or force, it will remain fixed in one position. The degree to which the rotor offers resistance depends on 3 things:
Mass of the rotor – greater the mass, greater resistance to change in direction of plane of rotation, Angular speed of
the rotor – higher the speed, greater the resistance, Radius of gyration of the rotor – bigger the radius, greater the
rigidity.
Gyroscopic Precession• angular change of direction of the plane of rotation of a gyroscope, as a result of an external
force.• The rate of this change can be used to give indications such as the turning rate of an aircraft. Determining Precession Direction• If a mass is mounted on a rotating shaft, and the centroid is offset from the axis
of rotation, mass will exert centrifugal force on the shaft.• Even if the eccentricity is small, force may be considerable
at high speed.• So, it will cause the shaft to bend.• If large stresses produced, will cause damage to bearing.• Addition
by vibrations from supports and surroundings will cause undesirable effect.• Some eccentricity is due to
manufacturing imperfections or design, so it is unavoidable.• Balancing is needed to eliminate effect of centrifugal
force.• Eg ; weights put on car wheels to balance them, make it easier to drive at high speed. Friction• Force that
resists any sliding movement between two contacting surfaces. Frictional force depends on nature between two surfaces• Acts in any directions but always acts in opposing motion. Angle of the plane ( ) is increased, the body remains stationary, until at some particular value of , it beginsθ θ to move down the plane• Coefficient of Static Friction• Static friction is friction between two solid objects that are not moving relative to
each other. The static friction force must be overcome by an applied force before an object can move. The maximum possible friction force between two surfaces before sliding begins is the product of the coefficient of static friction• sometimes referred to as limiting friction
Coefficient of Dynamic Friction• Dynamic friction is when two objects are moving relative to each other and rub together (like a sled on the ground)• The amount of force required to keep the object moving is called the coefficient of dynamic friction• usually less
than the coefficient of static friction for the same materials. There are several types of friction. Dry friction resists relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction
between nonmoving surfaces, and kinetic friction between moving surfaces. Fluid friction describes the friction between layers within a viscous fluid that are moving relative to each other• Lubricated friction is a case of fluid friction where a fluid separates two solid surfaces• Skin friction is a component of drag, the force resisting the motion of a solid body through a fluid•
Fluid – term used for liquid and gases. Specific gravity and density Density – mass per unit volume• Varies with Temperature (for solids and liquid) Temperature and pressure (gas) Density ( ) = mass volume•ρ Standard conditions for the measurement of gas density is established at 00C and a pressure of 1013.25 millibars
(Standard atmospheric pressure)• Temperature change will not change the mass of the substance, but as temperature
change, the substance tend to expand or contract, altering the volume. Relative Density• It is necessary to compare
density of one substance with the other to achieve a standard which all other substance can be compared• For solid
and liquid, compare with water at 4 0C.• For gas, compare with air. Relative Density = mass of any volume of a substance mass of equal volume of water / air• Eg ; if a hydraulic fluid has
relative density of 0.8, then 1L of the liquid wieghs 0.8 times as much as 1L of water. Hydrometer• Used to measure the relative density of liquids Viscosity• Measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress• Also
known as "thickness" or "internal friction“.
This internal friction opposes the motion of one layer over another and, when it is great, it makes the flow of the liquid very slow. Viscosity of a liquid rapidly decreases as its temperature rises.
Fluid Resistance Skin friction• Resistance present on a thin, flat plate which is edgewise on to a fluid flow.• Near the surface, the fluid is slowed up due to roughness of the skin, and fluid can also be considered as stationary at the
surface.• Effected by skin smoothness. The rougher the skin, the higher the friction.
Eddies or turbulent airflow• swirling of a fluid and the reverse current created when the fluid flows past an obstacle•The moving fluid creates a space devoid of downstreamflowing fluid on the downstream side of the object.
Eg. If you put plate at right angles to flow, turbulence will be created behind the plate and a very high resistance. Effect of streamlining• flowing steadily over a smooth surface, narrow layers of it follow smooth paths that are known
as streamlines. • This smooth flow is also known as laminar flow.• If laminar flow encounter obstructions, the
streamline will break and become irregular or turbulent.If fluid flows slowly along pipe, the flow is streamline. If flow
is very fast and exceedsa certain critical speed,the flow will become turbulent.
The Compressibility of Fluids• All fluids are compressible, so that their density will change with pressure. Fluid
assume as incompressible – provided under steady flow conditions, and changes of density small Gases easily
compressed – except when changes of pressure and density are small.
Static and Dynamic Pressure• Pressure acting on x x1 is due to the weight of the fluid acting downwards• W = mg ( g
= gravitational force ) mass = volume x density = height x crosssectional area x density = hA so, downwards force = h
. . g . A acting on Aand pressure will be = h g . A A =h gρ ρ ρ ρ
Bernoulli’s Theorem• a principle that explains the relationship between potential and kinetic energy in a fluid.• In
a fluid the potential energy is that caused by the pressure of the fluid, while the kinetic energy is that caused by the
fluid’s movement.• As a fluid enters a venturi tube, it is travelling at a known velocity and pressure.• When the fluid
enters the restriction it must speed up, or increase its kinetic energy. However, when the kinetic energy increases, the
potential energy decreases and therefore the pressure decreases.
Thermodynamics
First Law Energy cannot be created or destroyed. It can only be converted from one to another. When the energy
converts from one form into other forms the total quantity of energy remains the same.
Second Law Heat can only transfer from a high temperature region to a lower temper at region. It cannot naturally
transfer the other way.
Third Law The transfer of energy from matter becomes increasingly difficult as its temperature approaches absolute
zero. It is considered impossible at absolute zero.
Temperature• Heat is a form of energy that causes molecular agitation within a material. is a measure of the kinetic
energy of molecul Temperature scale; Freezing – 0degree C Boiling – 100C Fahrenheit Scale when you increased the temperature of a gas by one degree Celsius, it expands by 1/273 of its
original volum• So if the temperature was decreased to 273 degrees below zero, the volume of the gas would also
decrease to zero, and there would be no more molecular activity – absolute zero.• On the Celsius scale absolute
zero is – 273 C.
On the Fahrenheit scale it is – 460 0F
Heat• is the exchange of thermal energy from a hot body to a cold body.• When a hot body and a cold body have
contact, heat will flow from the hot body to the cold body until they both reach thermal equilibrium (they are at the
same temperature).• For example ;When an aircraft’s brakes are applied, the kinetic energy of the moving aircraft is
changed into heat energy by the rubbing action of the brake frictionmaterial against the brake discs.• SI system : Joule
(J) British thermal unit (Btu) calorie (cal) Heat & Work Conversion Factors 1J 0.2388 cal 1 cal 4.1868 J 1 Btu 1055 J 1J
0.000 947 Btu 1 Btu 0.252 cal 1 cal 3.968 Heat Capacity• specific heat amount of heat per unit mass required to raise the temperature by one degree Celsius.•
Relationship between heat and temperature change : Q = cmΔT Q is the heat added in 0C C the specific heat capacity in J / kg0C M is the mass in kg ΔT is Tfinal – Tinitial in 0C • Different materials require differing amounts of heat energy to change their temperature.• The heat energy required to change the temperature of 1 kg of material by 1 K is known as the specific heat capacity (c) of the material.• Due to the high specific heat of water, oceans and large lakes serve as temperature stabilisers.• Land surfaces have a much lower specific heat, and the temperature can vary significantly throughout the day. Heat Transfer• three methods by which heat is transferred from one location to another or from one substance to
another, which are : conduction convection radiation Conduction• When body having high heat energy in contact with body having low heat energy.• Eg; When hot object in contact with cold object, energy of molecules from hot object will be transferred to molecules of cold object until they have the same amount of energy ( stabilize ).• Various metals have different rates of conduction.• Liquids are poor conductors of heat in comparison with metals.• .Gases are even worse conductors of heat than liquids.• Insulators are materials that reduce or prevent heat conduction. Convection• process by which heat is transferred by the movement of a heated fluid.• Transfer of heat by
convection is often hastened by the use of a ventilating fan to move the air surrounding a hot object.• Eg ; when heat is absorbed by a freemoving fluid, the fluid closest to the heat source expands and its density decreases. Radiation• is the only form of energy transfer that does not require the presence of matter.• refers to the continual
emission of energy from the surface of all bodies.• This energy is known as radiant energy of which sunlight is a form.•
This is why you feel warm standing in front of a window whilst it is very cold outside Expansion and Contraction• All
materials expand and contract with a change in temperature. gases which expand the greatest amount . Solids and liquids expand much less than gases Volumetric Expansion• Expansion – considered as change in length, change in area or change in volume.• Different materials expand at different rates.Expansion of Solids• Expansion is proportional to the increase in temperature to
the original dimension and depends on the actual material used. L2 L1 = L1 ( 2θ θ α 1) L2 and L1 are final and initial lengths, 2 and 1 are final and initial temperatures is a materialθ θ α constant (coefficient of linear expansion). Expansion of Fluids• Fluids expand more than solids.• For gases, as volume and temperature changes are usually
accompanied by pressure changes.
The law of Thermodynamics• Thermodynamics is the study of the way that one does work with heat.• Energy
conservation limits the amount of work we can get out of a certain amount of heat.
First law of thermodynamics• States that energy is conserved.• The change in internal energy of a system is equal
to the heat added to the system minus the work done by the system. ΔU = Q – W (Δ is the mathematical symbol for a
change in a quantity) ΔU is the change in internal energy, Q is the heat added to the system W is the work done by the
system.• ΔQ is positive if it is put into the system, negative if it is taken out of the system.• ΔW is positive if the system
does work on its surroundings and is negative if work is done on the system.• The internal energy is the sum of the
kinetic and potential energy of the atom and molecules that make up the system. second law of thermodynamics•
general principle which places constraints upon the direction of heat transfer and the attainable efficiencies of heat
engines.• States that heat transfer will occur naturally of
its own accord down the temperature gradient.• Heat will naturally flow from a hot region to a cool region but not the other way around.
the basic sense of the principle : Heat will not flow spontaneously from a cold object to a hot object. You cannot create
a heat engine which extracts heat and convertsit all to useful work. There is a thermal bottleneck which constrains devices whichconvert stored energy to heat and then use the heat to accomplishwork.
gases• Ideal gas one in which all collisions between atoms or molecules are perfectly elastic and in which there
are no intermolecular attractive forces.• a collection of perfectly hard spheres which collide but which otherwise do
not interact with each other.• all the internal energy is in the form of kinetic energy and any change in internal energy
is accompanied by a change in temperature.
From the Ideal Gas Law ; = Boyle’s Law If temperature is constant ; P1V1 = P2V2Charles’ LawIf pressure is constant ; = Isothermal and
Adiabatic Processes
Isothermal process in which the temperature in a system remains constant. Adiabatic process one where no heat is added to, or taken away from thesystem.Heat engine• heat engine is a
system that performs the conversion of heat or thermal energy to mechanical work. Heat Engine Processes• a useful process is the adiabatic process where no heat enters or leaves the system.• The first law of thermodynamics with Q=0, i.e. heat = zero shows that all the change in internal energy is in the form of work done.• internal energy is proportional to temperature, there is no change in the internal energy of the gas during an isothermal process.• All the heat added to the system is used to do work. Engine Cycle Carnot Cycle• consisting of two isothermal processes and two adiabatic processes.• can be thought of as the most efficient heat engine cycle allowed by physical laws.• the Carnot efficiency sets the limiting value on the fraction of the heat which can be so used.• In order to approach the Carnot efficiency, the processes involved in the heat engine cycle must be reversible and involve no change in energy available to do work.• This means that the Carnot cycle is an idealisation, since no real engine processes are reversible and all real physical processes involve some increase in energy available to do work .
Heat Flow to Hotter Region• internal energy will not spontaneously flow from a hot region to a cold region.• But if external force is given, heat can flow from cold region to hot region.• Usually this is done with the aid of a phase change, i.e., a refrigerant liquid is forced to evaporate and extract energy from the cold area. . Then it is compressed and forced to condense in the hot area, dumping its heat of vaporisation into the hot area. Refrigerator Heat Pump Optics ( light ) Speed Of Light• is one form of transmission of Electromagnetic energy.• travels at high speed (about 3 x 108 metres
per second) and in straight lines.• Can be ‘bent’ or reflected. Laws Of Reflection and RefractionReflection• Light can also be reflected.• Observation and measurement will show that ; a. the incident and reflected rays lie in the same plane. b. the angle of incidence equals the angle of reflection. Plain and Curved Mirrors• When you look in a mirror, you see a reflection, usually termed an image.• For example, if an object is viewed from two different angle, the reflected rays : – appear to come from which corresponds to the
image. – lies on the same normal to the mirror as the object. – appears the same distance behind the mirror as the object is in front. – Appears as the same size.
For mirror that is not plain, it may be curved, s
pherical and parabolic.• Incidence equals reflection still holds, but the curved surface allows the rays to be focused
or dispersed. FP is known as the focal length. Note the rays actually pass through F, and a real image can be formed.
FP is still the focal length, but the image is virtual. The size of the image depends on the position of the object.• image may be smaller or larger.• If the object is near to the mirror, the image will be far and larger from the mirror but in opposite plane.• If the object is far from the mirror, the image will be nearer and small, between the position of object and mirror in opposite plane. magnification = image height object height• For spherical mirror, magnification = image distance object distance Concave mirrors (e.g. shaving mirrors) give a magnified, erect (right way up) image, if viewed from closeto.• Convex
mirrors (e.g. driving mirrors) give a smaller, erect image, but with a wide field of view.• Parabolic reflectors can focus
a wide parallel beam. By placing the bulb at the focus, they can produce a strong beam of light. (Conversely, they can
focus microwave signals when used as an aerial). Refraction• A submerged object is often seen at reduced depth.• This is because the ray has been ‘bent’ at the
water / air boundary. Refraction Index• Since the angle of incidence and refraction is not the same ; sine i = μ ( a constant ) sine r•
depends on the 2 mediums involved. μ = speed of light in medium 1 speed of light in medium 2 Ray (1) has been refracted across theboundary, but ray (2) has been internally reflected at the boundary. Critical angle of incidence when the ray in thedenser medium does not emerge, but travelsalong the boundary.• sine C = 1 / μ exists• Refraction is the basic principle which explains the workings of prisms and lenses.
Total Internal Refraction• Refraction at a denser medium, a beam of light is bent towards the normal and, vice versa.• APB – ray reflected away.• AP’D – angle of incidence increased, angle of refraction becomes 900 .• AP”C – Angle of
incidence further increased , angle of refraction is >900 , remaining in the boundary.• Total internal refraction – where none of lights passing through the boundary.
Convex and Concave Lenses• The light rays then meet the surface of the lens at an angle to the normal, and are then refracted.• Images can be real or virtual, erect or inverted, and larger or smaller.• The nature of the image will depend on the type of lens, and the position of the object in relation to the focal length of the lens, (the focal length is a function of the curvature of the lens surfaces).
Fibre Optics• Depends upon the total internal reflection of light rays.• Light can be trapped by total internal reflection inside a bent glass rod and piped along a curved path as in the diagram below. a single, very thin glass fiber behaves in the same way.• They are small and so, once light is introduced into the fiber with an angle within the confines of the numerical aperture of the fiber, it will continue to reflect almost losslessly off the walls of the fiber and thus can travel long distances in the fiber.• If a bundle of parallel fibers is used to construct an optical transmission line, images can be transferred from one point to another.
Fibre Optic Imaging• Principle : light striking at one end will be transmitted to the other end of the fibre.• If the
arrangement of fibres in the bundle is kept constant then the transmitted light forms a mosaic image of the light which
struck the end of the bundle. Wave motion and sound
Wave motion• For example, wave is created at a lake or pond due to disturbance, such as a rock thrown into the water.• The water wave has a crest and a trough and travels from one location to another.• One crest is often followed by a second crest which is often followed by a third crest, and so on.• waves may be circular waves which originate from the point where the disturbances occur; such circular waves travel across the surface of the water in all directions.
Another example, if a slinky is stretched out from end to end, a wave can be introduced into the slinky by either
vibrating the first coil up and down vertically or back and forth horizontally.• As the wave moves along the slinky, each
individual coil is seen to move out of place and then return to its original position.• The wave does not stop when it
reaches the end of the slinky; rather it seems to bounce off the end and head back from where it started.
Categories of Waves• Waves come in many shapes and forms.• Some share basic characteristic properties and behaviors, some waves can be distinguished from others based on some very observable (and some nonobservable) characteristics.• It is common to categorise waves based on these distinguishing characteristics. Transverse Wave Direction of movement Longitudinal wave Surface Wave To categorize wave Electromagnetic Waves Ability to be
transmitted through vacuum Mechanical Waves
Direction Of Movement Transverse wave• Wave moves in a direction perpendicular to the direction which the wave moves.• If pulse is applied to the left end by vibrating it up and down, the energy will be transported from left to right
and particle will be displaced upwards and downwards.
Longitudinal Wave• Wave in which particles of the medium move in a direction parallel to the direction which the
wave moves.• If force is applied to the left end by vibrating it left and right, the energy will be transported from left
to right and particle will be displaced rightwards and leftwards.
Ability to transmit through vacuum Electromagnetic Wave• wave which is capable of transmitting its energy through a vacuum.• Electromagnetic waves are produced by the vibration of electrons within atoms on the Suns surface.• These waves subsequently travel through the vacuum of outer space, subsequently reaching Earth.• Eg ; Light Wave.Mechanical Wave• Wave which is not capable of transmitting its energy through a vacuum.• Require a medium in order to transport their energy from one location to another.• Eg ; Sound Wave.
Anatomy of Waves• dashed line equilibrium or rest position of the string. (if there were no disturbance moving through it )• Points A and F crests of this wave (point on the medium which exhibits the maximum amount of positive or upwards displacement from the rest position)• Points D and I troughs of this wave (point on the medium which exhibits the maximum amount of negative or downwards displacement from the rest position )
Amplitude of a wave maximum amount of displacement of a particle on the medium from its rest position. ( from
rest to crest )• Wavelength ; a. Simply the length of one complete wave cycle. b. Wave has a repeating pattern. And the length of one such repetition (known as a wave cycle) is the wavelength. c. Can be measured as the distance from
crest to crest or fromtrough to trough. ( B – G, E J, D – I )
Longitudinal wave• is a wave in which the particles of the medium are displaced in a direction parallel to the direction of energy transport.• Wavelength determined by measuring the distance between any two corresponding points on adjacent waves. ( measure distance from a compression to the next compression or from a rarefaction to the next
rarefaction ; A – C , B – D )
Frequency and Period of a Wave• Frequency ; a. refers to how often the particles of the medium vibrate when awave passes through the medium. b. number of complete vibration cycles of a medium per a givenamount of time and it as the units of cycles per second or Hertz (Hz)where 1 Hz is equivalent to 1 cycle/second. c. . A detector could be used to detect the frequency of these pressure oscillations over a given period of time. d. unit : Hertz, Hz ( cycle / sec )• Period ; a. the time which it takes to do something. b. the time for a particle on a medium to make one complete vibration cycle. c. When an event occurs repeatedly, then we say that the event isperiodic. d. measured in units of time such as seconds, hours, days or years.
Interference Phenomena Wave interference• phenomenon which occurs when two waves meet while travelling along
the same medium.• Causes the medium to take on a shape which results from the net effect of the two individual
waves upon the particles of the medium.• Eg ; if 2 crests of wave having amplitude of +1 move into each other, the
resulting sine crest +2 is created at the moment when the 2 waves overlapped.• Sometimes called Constructive
Interference.
Constructive Interference• Occurs at any location along the medium where the two interfering waves have a
displacement in the same direction.• If both waves have an upward displacement; consequently, the medium has an upward displacement which is greater than the displacement of the two interfering pulses.
Destructive Interference• type of interference which occurs at any location along the medium where the two
interfering waves have a displacement in the opposite direction.• If a sine crest with an amplitude of +1 unit meets a sine trough with an amplitude of 1 unit, destructive interference occurs.• The two pulses cancel each other for the duration of the overlap.• Once the two pulses pass through each other, there is still a crest and a trough heading in the same direction which they were heading before interference.
Principle of Superposition“ When two waves interfere, the resulting displacement of the medium at any location is
the algebraic sum of the displacements of the individual waves at thatsame location.”• To determine the shape of the
resultant wave caused by the interference of two separate waves.• Standing Wave pattern : An interference
phenomena. When the vibration frequency of the source causes reflected waves from one end of the medium to
interfere with incident waves from the source in such a manner that specific points along the medium appear to be
standing still. Only created within the medium at specific frequencies of vibration; these frequencies are known as
harmonic frequencies, or merely harmonics. From the presence of two waves (sometimes more) of the same
frequency with different directions of travel within
Antinodes point A on the medium moves from a positive to a negative displacement over time.• Nodes point B on
the medium is a point which never moves.
Standing Wave• stationary wave is a wave that remains in a constant position.• often applied to a resonant mode of an extended vibrating object.• created by constructive interference of two waves which travel in opposite directions in the medium, but the visual effect is that of an entire system moving in simple harmonic motion.• modes of vibration associated with resonance in extended objects like strings and air columns have characteristic patterns called standing waves.• arise from the combination of reflection and interference such that the reflected waves interfere constructively with the incident waves.• An important part of the condition for this constructive interference for stretched strings is the fact that the waves change phase upon reflection from a fixed end.
Sound• Sound wave pressure disturbance which travels through a medium by means of particle interaction.• As one particle becomes disturbed, it exerts a force on the next adjacent particle, thus disturbing that particle from rest and transporting the energy through the medium.• speed of a sound wave refers to how fast the disturbance is passed from particle to particle.• frequency refers to the number of vibrations which an individual particle makes per unit of time.• speed refers to the distance which the disturbance travels per unit of time.
Speed of Sound• Is determined to be 331 ½ m / s at 00C – 1087 ft /s , 741 mph or 644 kts.• liquids are better transmitters of sound.• Eg. sound waves travel approx. 4 times faster in water than in air and speed of sound in solids is even greater, sound travels through steel is 15 times faster than it travels in air. speed ( sound wave ) = frequency x wavelength• Alteration in wavelength effects the frequency, but not the wave speed.• Doubling of wavelength results in halving the frequency, but wave speed doe not change.• The speed of sound wave depends on the properties of the medium through which it moves.
Primarily affected by temperature, the lower the temperature, the lower the speed of sound. speed of sound = √ ( R T ) where = ratio of specific heats of the gas R = gas constant T = gas temperature ( in Kelvin )•γ γ It determines the nature and formation of shock waves. Mach No = True Airspeed of aircraft Speed Of Sound
Intensity• amount of energy which is transported past a given area of the medium per unit of time.• Often referred
to as ‘loudness’ , the energy of the wave.• The greater the amplitude of vibrations of the particles of the medium, the
greater the rate at which energy is transported through it, and the more intense that the
sound wave is.• Intensity is the energy/time/area; and since the energy/time ratio is equivalent to the quantity power, intensity is simply the power/area. Intensity = Energy or Intensity = Power Time x Area Area• Eg ; if amplitude of sound wave is doubled, intensity will increase fourfold.• Unit : Watts / Meter2 . But scale to measure intensity; Desibel (dB)
Pitch• Best described as position on musical scale.• The ears of humans (and other animals) are sensitive detectors capable of detecting the fluctuations in air pressure which impinge upon the eardrum.• The human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz.• The sensations of these frequencies are commonly referred to as the pitch.• A high pitch sound corresponds to a high frequency and a low pitch sound corresponds to a low frequency.
Doppler Effect• effect produced by a moving source of waves in which there is an apparent upward shift in frequency
for the observer and the source are approaching and an apparent downward shift in frequency when the observer and the source is receding. • Occur with all types of waves most notably water waves, sound waves, and light waves.
Doppler Effect observed because the distance between the source of sound and the observer is changing.• If the
source and the observer are approaching, then the distance is decreasing and if the source and the observer are
receding, then the distance is increasing.• If the source is moving towards the observer, the observer perceives sound
waves reaching him or her at a more frequent rate (high pitch); and if the source is moving away from the observer,
the observer perceives sound waves reaching him or her at a less frequent rate (low pitch).