Physics 2 Flashcards
Define heat?
Transfer of energy due to a difference in temperature
Define temperature?
Measure of hotness or coldness of an object
Define thermal energy?
Amount of total energy an object contains due to the kinetic motion of its particles
Four different temperature scales?
- Celcius - Most commonly used scale
- Kelvin - Scientific measurements
- Fahrenheit - Commonly used in the USA
- Rankine - Mechanical engineering
Define absolute zero?
- Theoretical lowest possible temperature that can be achieved
- The point at which all atomic motion is assumed to stop and kinetic energy is zero
Temperature scale commonly used for mechanical engineering?
Rankine
Temperature scale commonly used for scientific measurements?
Kelvin
How does a liquid thermometer work?
- A the temperature rises, the liquid heats up and expands through thermal expansion - thus rising in the tube and indicating the temperature
- Temperature is read upwards
How does a gas thermometer work?
- When heated, the air expands and pushes the water down the glass tube
- When cooled, the air contracts and the water rises
- Temperature is read downwards
Define thermocouple? How does it work?
2 pieces of dissimilar metal wires form a circuit where the 2 junctions are hot and cold (when one is heated, the other is kept at room temp), this creates an electromotive force and the current begins to flow
How does a resistive thermometer work?
- Costant current is pushed through resister
- Resister placed in area that you want to measure the temperature
- As temp increases, the resistance also increases slowing the current down
- The difference in current is used to calculate temperature
Define heat transfer via convection?
- Process of heat movement that happens inside a fluid, as the fluid heats, it expands and becomes less dense - this creates buoyancy
- Displaced air / fluid - The cooler air / fluid at the top is forced to the bottom to create circulation
Define heat transfer via radiation?
- Does not require a medium to travel
- Transfers heat via electromagnetic radiation and travels through the vacuum of space
- Transfers in waves at the speed of light
Define heat transfer via conduction?
- Must be touching to have heat transfer
- Vibration of hot particles are transmitted via contact to the colder particles, making them all vibrate quicker
Can heat generated by conduction and convention travel through a vacuum?
No
If the kinetic energy between 2 substances is shared, what will happen to the temperature of the substances?
Thermal equilibrium will be achieved
First law of thermodynamics?
The increase in the energy of a thermodynamic system is equal to the amount of heat added to the system, minus the work done by the system on the surroundings
Equation for the first law of thermodynamics?
Change in internal energy = heat added to the system - work done by the system
Second law of thermodynamics?
- When energy is transferred from one form to another, entropy increases and energy decreases
- No process is 100% effective
Define entropy?
The measure of disorder in a system - randomness
Equation for work done by expanding gases?
W = f x s
Work done = force x displacement
Example of work done by expanding gasses in aerodynamics?
Gas turbine engine
How is specific heat of a gas at a constant pressure different to specific heat of a gas at constant volume?
Constant volume: all heat energy is used to raise the energy of the gas and its
temperature
Constant pressure: All heat energy causes the gas to expand (to do work), not all of the heat energy is being used to raise the temperature
Term given to the simplified version for gas behaviour?
Ideal gas laws
What is an Isothermal process?
Explain the proportionality equation?
Another name for this process?
Iso - Constant
Thermo - Temperature
Define Boyle’s law
- Maintaining / locking the temperature
- When the volume remains the same, but space changes, the pressure changes
Volume increase = pressure decrease
Volume decrease = pressure increase
Isobaric process?
Explain the proportionality equation?
Another name for the process?
Charles’ law -
Locking pressure (directly proportional)
REMEMBER: King Charles singing under pressure
Volume increase = temperature increases
Volume decrease = temperature decreases
Explain an isochoric process?
Explain the proportionality equation?
Provide another name for this process?
Pressure law - also known as Gay-Lussac’s Law (nothing to do with pressure)
Iso - Constant
Choric - Volume
- Locking volume
Temperature increase = pressure increase
Temperature decrease = pressure decrease
REMEMBER - Gays are loud
Define the general gas law?
Pressure x Volume = Temperature (at constant volume)
PV=T
Define adiabatic processes?
No heat enters or leaves the system
What happens to the temperature and pressure during adiabatic compression?
Increase in temperature and pressure
What happens to temperature and pressure during adiabatic expansion?
Temperature of the gas will decrease
Engine cycle - in correct order - for an internal combustion 4 stroke engine?
- Intake
- Compression
- Power
- Exhaust
Describe the engine cycle for an internal 4 stroke combustion engine?
Suck, squeeze, bang, blow
1) The piston is pulled down inside the cylinder by the momentum of the crankshaft. The inlet valve opens, sucking in a mixture of fuel and air into the cylinder
2) The inlet valve closes, the piston moves back up the cylinder and compresses the fuel-air mixture.
When the piston reaches the top of the cylinder, the spark plug fires
3) The spark ignites the fuel-air mixture causing a mini explosion. The fuel burns immediately, giving off hot gas that for an instant raises the pressure dramatically and keeps the volume is unchanged. The piston is then pushed down releasing the energy from the fuel powering the crankshaft.
4) The outlet valve opens. It forces the exhaust gases out through the exhaust outlet.
Example of an adiabatic process within the internal combustion 4 stroke engine cycle?
Power stroke - ignite and goes bang
Why is a 4 stroke piston engine process considered to be a constant volume engine?
- Constant volume is injected into the system
(Otto cycle)
Why is the Brayton cycle in a gas turbine engine considered to be a constant pressure cycle?
- Suck, squeeze, bang, blow but simultaneously
- Constantly under pressure
How does a refrigerator/heat pump work?
- Absorbs heat energy from inside and transfers it outside
Define each part of the refrigeration process?
1) The compressor motor forces a coolant gas at high pressure through the condenser
2) As the coolant flows through thin radiator pipes in the condenser on the back of the fridge, heat is given
out and it condenses back into a liquid
3) The liquid coolant undergoes a sudden drop in pressure that
makes it expand
4) The coolant absorbs and removes heat from the food inside
5) Warmed gas is then returned to the compressor and re-compressed as the cycle
continues
Difference between a heat pump and a refrigerator?
Vapour cycle is reversed
Why are both refrigerators and heat pumps considered isothermal processes?
Constant temperature is maintained in both systems
If you raise the temperature of an ideal gas inside a cylinder with a fixed piston, what will happen to the pressure of the gas inside the cylinder?
- Increase pressure
- Isochoric process
Define latent heat?
Amount of heat required to cause a change in heat
What does latent heat of fusion describe?
Heat needed to change a solid into a liquid
Note - Fusion for white choc fusion
What does latent heat of vaporisation describe?
Heat needed to change a liquid into a gas
Note - Vapour for gas
If an ideal gas has its temperature locked and the container holding it is compressed - what happens to the pressure of the gas?
- Based on Boyle’s law the pressure will increase
- Isothermal process
Define combustion?
Heat combustion is the heat released during the reaction
What happens during the process of combustion?
Hydrocarbon reacting with oxygen resulting in heat, carbon dioxide and water
Why are heat combustion valves important when comparing fuels?
The greater the heat of combustion of a substance the greater the amount
of energy produced when the fuel is burned
Define heat capacity?
Amount of heat required by a substance to rise a certain amount
Formula for heat capacity?
Q=CAT
Energy = heat capacity x change in temperature
Define the characteristics of a substance with a low heat capacity?
- Requires little to no heat to rise to a certain amount
- Metals like copper
Give an example of a substance with high heat capacity?
- Requires a lot of heat to rise a small amount
- Fibres like asbestos
Define heat specific?
- The amount of heat needed to rise the temperature of a substance
- Helps to determine if the substance is a conductor or insulator of heat
Formula for heat specific?
C = Q / m x AT
Specific heat = heat energy / mass x temperature change
OR
Q = MCAT
Heat energy = mass x specific heat x temperature change
Which temperature scales start at absolute zero?
- Kelvin
- Rankine
How do you convert degrees Celsius to Kelvin?
Kelvin = Celsius + 273
How do you convert from Kelvin to degrees Celsius?
Celsius = Kelvin - 273
How do you convert from Fahrenheit to degrees Rankine?
Rankine = Fahrenheit + 460
How do you convert from Rankine to Fahrenheit?
Fahrenheit = Rankine - 460
What is light?
All electromagnetic radiation
What is the speed of light in a vacuum?
3 x 10 to the power of 8 m s -1
What is a plane surface?
2D, perfectly flat surface that extends in all directions
What does ‘normal’ refer to when referring to a plane surface?
A line drawn perpendicular to the surface at the point of contact of the light ray
What is an incidental ray?
The incoming light ray moving towards the surface
What is a reflected ray?
The outgoing light ray reflected away from the surface
State the law of reflection?
The angle of incidence equals the angle of reflection
What is the main problem encountered when light reflects off a spherical reflector?
- Spherical aberration (results in poor focus of an image)
- Multiple focal points
How can we limit the effects of spherical aberration?
- Limiting the curvature
- Only using the central portion of the reflector
Main difference between spherical and parabolic mirrors?
- Spherical mirrors have uniform curvature and are part of a sphere
- Parabolic mirrors can be manufactured to give perfect focus
What is refraction?
Bending of light
What happens to light when it moves from a less dense medium to a more dense medium?
Slows down and bends towards the normal
What happens to light when it moves from a more dense medium to a less dense medium?
Bends away from the normal
What will light do when it passes through a convex lens?
Bend and converges together
What another term used to describe convex?
Converging lens
How are convex lenses used by aviation technicians?
Magnified glass used to make objects appear closer and clearer
What happens to light when it initially enters a fibre optic cable?
It is refracted
What is the importance of the acceptance angle in fibre optic operations?
Affects the propagation of the light rays once they enter the core
What is the importance of total internal reflection when dealing with fibre optic cables?
- Allows light / signal to be contained in the core
- Minimises loss of transmission signal
Name 3 applications for fibre optic cable in aircraft systems?
- Communication
- Automatic flight controls
- Navigation
Name 3 advantages for fibre optic cables in aircrafts?
- Light weight
- No electromagnetic interference
- Complete electrical isolation
Name 2 disadvantages for fibre optics in aircrafts?
- Radiation
- Glass cut offs
(Both above are safety concerns) - Not as flexible
- Difficult to repair
Define the term wave?
Energy carriers, can move energy without moving the matter itself
Define the term damping?
Air resistance / friction
Define equilibrium position?
Natural resting position
Define periodic motion?
Motion that is regular and repetitive, such as a vibration
Define sinusoidal wave motion?
All naturally occurring periodic motion will produce a wave as the object oscillates around the equilibrium point.
How is the height of a waveform defined?
Measure from crest to crest
Define the term restoring force with reference to simple harmonic motion?
- Restoring force which always acts toward the equilibrium position, no matter where the object is
- If there were no restoring forces, damping would not occur and the vibration would continue on forever
The further an object moves from its equilibrium position, the less the restoring force becomes? True or false?
False - further the object is away from the equilibrium the greater the force becomes
Define resonance with reference to pendulums?
If the forces vibration is timed to match the natural
frequency, resonance will occur. This resonance will have the effect of increasing the amplitude of the vibration that occurs within the swinging pendulum.
Define fundamental frequency?
- Also known as first harmonic
- Natural frequency
Another name for fundamental frequency?
First harmonic
Define harmonics?
Multiples of a fundamental frequency
If a fundamental frequency is determines to be 60HZ, what is the forth harmonic?
240HZ
What is a mechanical wave?
Waves in which matter vibrates and the energy is transferred through a medium
How are mechanical waves different to electromagnetic waves?
Mechanical waves - require a medium
Electromagnetic waves - do not require a medium
2 types of mechanical waves?
- Transverse waves
- Longitudinal waves
What is the difference between transverse and longitudinal waves?
Transverse waves:
- Travel with the shape of a sin / cosine wave
- Move perpendicular
- Measured peak to peak
- Also known as sinusoidal waves
Longitudinal waves:
- Parallel to proportion
- Particles isolate back and forth
- Also known as compressional waves
Components of a transverse wave?
- crest / trough
- wavelength
- amplitude
- Equilibrium position
Components of a longitudinal wave?
- Areas of compression
- Refraction
What type of wave is a sound wave?
Longitudinal mechanical waves
Define frequency in reference to wave motion?
Amount of cycles per second
How do you measure the wavelength?
Crest to crest or trough to trough
How are period and frequency related?
Period is inversely proportional to frequency and vice versa
2 factors that determine the speed of a wave?
- Wavelength
- Frequency
A wave has a frequency of 50HZ and a wavelength of 2.4m. How fast is it travelling?
120m s -1
Define phase shift?
How much one sine wave is shifted relative to another
What is wave interference?
When two (or more) waves are travelling in the same medium and they meet, the displacements are added
to produce a resultant waveform
What is constructive interference and how might it occur?
- Peaks line up
- Summing affect
- Resultant amplitude will be greater than a single wave on its own
What is destructive interference and how might it occur?
- Two waveforms occurs at a time out of phase
- Cancel each other out when added together (same amplitude)
What does a standing wave look like?
It appears to stand still
Example for how destructive interference is applied in aviation?
Noise cancelling headphones
What causes a standing wave?
- When waves are reflected off of a surface
- Same wave length etc but are now out of phase
- Appear to be standing still
What are 2 parts of standing waves?
- Node
- Antinode
How do the 2 parts of a standing wave differ from each other?
What is a sound wave?
- Sound is a property of vibrating objects
- Needs matter to operate
How does a sound wave travel when given off from an object like a tuning fork?
- Mechanical disturbance causing it to vibrate
What 3 factors affect the speed of sound?
- Elasticity
- Density
- Temperature.
What would an increased in density do to the speed of sound in the air?
Reduction in speed
What would an increase in temperature do to the speed of sound in air?
Increase in speed
Which characteristic has the greatest effect on the speed of sound?
Elasticity
In terms of sound waves, what does sound intensity relate to?
Measure of amount of energy that can be transferred
What is the SI unit for acoustic power?
Watts per meters squared
Define the loudness of sound?
- Measurement of the ear’s response to sound
What is the sound intensity level and how is it measured?
Logarithmic ratio
3 factors that determine sound quality?
- Harmonic content
- Attack and decay
- Vibrato.
What is harmonic content?
Contain a fundamental frequency, but also multiples of it
What is attack and decay?
Attack: determines how long a sound takes to reach its full amplitude
Decay: how long the sound
lasts
What is vibrato?
Periodic changes in the pitch of a tone
How does the doppler effect occur?
- Change in apparent frequency by an observer is known as the Doppler Effect
EXAMPLE -
Train coming towards you = compressing the air = higher pitch
Train passes and continues away from you = air particles are spread further apart = lower pitch
How are the pitch of sound and frequency related?
Preserve high frequency has high pitch etc
Would a higher or lower frequency be heard is a source of sound was moving towards the receiver?
Higher as it approaches
Will the doppler effect be heard if there is no relative movement between the source and receiver of sound?
No
