Unit 5 Physics Flashcards
Power, Watt, Kilowatt, Megawatt, Gigawatt
the rate of using energy doing work measure in watt (W) = j/s
kilowatt (kW) = 1000 Watt
megawatt (MW) = 106 Watt
gigawatt (GW) = 109 Watt.
Convert Degrees To Kelvin
oC to Kelvin by adding 273.15 K,
kelvin to 0C by subtracting 273.15
Pressure,
Newton Per Meter Squared
liquid/gas exerts pressure in all directions
measure in pascals {Pa] = newton per meter squared {Nm2}
Work Done As Energy Transferred
Work is the measure of energy transfer when a force (F) moves an object through a distance (d). Energy transferred and work done are both measured in joules (J).
force and displacemt
Work done = Force × Distance Moved In Direction Of Force {∆X }
pressure and volume
work done = pressure x change in volume of gas
Efficiency =
Useful Energy Output / Total Energy Input
Ideal Gas Equation
Pv = Nkt n= number of particles k= 1.38 x 10 ^-23 j/l t= temprature
Law Of Conservation Of Energy
The law of conservation of energy states that energy can neither be created nor destroyed - only converted from one form of energy to another. This means that a system always has the same amount of energy, unless it’s added from the outside.
system
the part of the universe whose properties you
are investigating. It is enclosed by a boundary defined
by you, the experimenter.
surroundings
the rest of the universe, outside the system boundary
Internal Energy (U),
The internal energy is the total amount of kinetic energy and potential energy of all the particles in the system. When energy is given to raise the temperature , particles speed up and gain kinetic energy.
∆U=U2 - U1
First Law Of Thermodynamics
(Q = ∆U + W)
heat in = energy change in the system + work out
Qin - Qout = ∆U + W
Isothermal
two bodies in thermal equilibrium
heat can flow in either direction reversibly
0 temperature difference = no net heat transfer
Adiabatic Processes
work input = internal energy gained
-w = ∆U, no energy wasted compressing gas leads to a corresponding temperature rise
Second Law Of Thermodynamics
A natural process can never be reversed in its entirety.
It is impossible to completely change heat into work.
Heat will not flow from a colder body to a hotter one without an input of work.
You cannot reverse the direction of time
Heat Refrigerators Pumps
refrigrators cool and enclosed space and reject heat from the outside
heat pumps draw heat from the ground or outside air and move that heat at a higher tempreture positioning of the heat exchanges
which space is bung contrilled
Maximum Theoretical Coefficient Of Performance (Cop)
minimise temp gapexpand a liquid bevause the volume is small
cut friction of vicous flow losses
keep compression work low
Idealised Engine Cycles
1–2 adiabatic compression – zero heat transfer.
2–3 isothermal expansion – heat absorbed by the system, Qin
3–4 adiabatic expansion – zero heat transfer
4–1 isothermal compression – heat absorbed by the
system, −Qout
For Heat Engine - Efficienty And Maximum Theoretical Efficiency
real engine can achieve a thermal efficiency higher than that of an ideal reversible engine operating between the same temperatures. (If this were not so it would be possible to create a machine that violated the Second Law and moved heat from a colder to a hotter body without doing work.) In practice, engine efficiency is always lower than this because all real engines have irreversible processes that produce less net work output and instead output more heat at the low temperature.
Transfer Of Energy Producing Temperature Change Or Changes Of State,
heat transfers,q, into the system counts as positive; flows out count as negative.
work done by system counts aas positive
direction of heart transfers depends on the tempratures outside the system,
Thermal Capacity,
the number of heat units needed to raise the temperature of a body by one degree.
Thermal Equilibrium
exists when two systems are in thermal contact, but there is no net transfer of heat because they are at the same temperature
Specific Heat Capacity
increase the temperature of 1kg by kelvin or oC
(∆Q = Mc∆T)
Specific Latent Heat From
(∆Q = ∆Ml),
Fusion,
Vapourisation
reverse process of solid melting to a liquid is called fusion /ice to water= 333.6kjk-1
the change of physical state from liquid to gas water tp steam = 2.26MJkg1
elastcitcty
when a solid material is able to regain its original dimensions after the applied force is removed.
hooks law
force is proportional to extension. k is constant
F = k Δx
e= stress / strains
elastic limit
point on the stress-strain curve, beyond which a material begins to suffer plastic deformation, and so will not completely regain its original dimensions when the stress is removed.
strength
the maximum stress that the material can bear. This occurs just before the material fails and fractures.
yield point
the point where the start of plastic flow causes a change of slope on the stress-strain curve. Iron and steel and a few other metals show a clearly defined yield with a drop of stress, while in many other materials the exact position of the yield point is hard to spot.
plastic deformation
occurs under stress levels that are sufficient to make the solid material begin to flow, rather like a liquid. When the stress is removed, a change in an object’s shape and size remains. This is called a permanent se
stress
force / cross sectional area
units = nm2 or Pa
strain
extension/ original length
no units
ductility
the ability of a material to be formed by drawing into new shapes, primarily by means of tensile forces.
brittleness
the tendency of a material to fracture under stress.
malleabillity
the ability to be shaped by means of compressive forces such as occur in rolling, hammering or stamping.
elastic hysteresis
occurs in materials like rubber, where internal friction between large molecules dissipates energy producing heat. Loading and unloading of a sample each produces a different stress strain curve, creating a hysteresis loop, the area of which represents the energy absorbed in the cycle
creep
when a material under stress deforms gradually over time. It is more severe in materials that are subjected to heat for long periods.
fatigue
the embrittlement and failure of a material that can occur with relatively low levels of stress if these are repeatedly applied and then relaxed over many cycles.
Density
Density, mass of a unit volume of a material substance. The formula for density is d = M/V, where d is density, M is mass, and V is volume. Density is commonly expressed in units of grams per cubic centimetre
Tensile/Compressive Stress
tensile stress, τ, is defined as: (force applied)/ (cross-sectional area of the sample)
τ = F/A
Tensile/Compressive Strain
tensile strain, σ, is defined as: (extension)/(original length of the sample)
σ = Δx/L
Elastic Strain Energy
calculating the area under the the force-extension grap
young modulus
e= stress/strain
nm2 or Pa
fluid flow patterns
transmit pressure, to transfer heat or to simply deliver quantities of substance to a new location. involves layers of molecules sliding over one another.
streamline
occurs at lower values of flow rate and pressure difference.
drift velocities of particles are all parallel and in the same sense
fluid in contact with a solid surface has the same velocity as that of the surface
velocity changes across the flow of the stream
most energy efficient type of flow
turbulent flow
occurs at higher flow rates
includes rotational flows
absorbs much more energy generates more resistance to flow
is chaotic - more complex
viscous drag
a kind of internal friction – between the layers, but it is the most energy efficient kind o
viscosity
dynamic viscosity
layers of fluid moving at different speeds cause a velocity gradient
change on u/ change in y
f/a=t=n (change on u/ change in y )
viscous drag
a kind of internal friction – between the layers, but it is the most energy efficient kind flow
shear stress measured in nm2 / Pa
Mass Of Fluid Flow Per Second For All Points Along A Pipe Or Stream Tube Is Constant
mass flow rate am/at must be the same entering system leaving from its outlet crossing every boundary along its length you can measure mass flow at any [point along the flow
bernoulli’s principle
1/2 mv2 + mgh +pV = constant value
1/2 v2 + gh + p/p = constant value where p is density
velocity increase pressure decreases as long as height is the same
shear thinning and shear thickening fluids
change viscosity as soo as there is a shear stress
mostly these are colloidal suspensions of solid particles or droplets in a liquid
brushing sliding or string a liquids provides shear stress.
shear thinning and shear thickening fluids
change viscosity as so as there is a shear stress
mostly these are colloidal suspensions of solid particles or droplets in a liquid
brushing sliding or string a liquids provides shear stress.
time dependent behaviours
thixotropic fluids thin gradually on stirring then slowly reset
e.g. yoghurts, jellies
rheopectic behaviour is rare time dependent thickening with shear stress, thinning again when it stops.
e.g synovial joint
