physics Flashcards
what is power
the rate of doing work
what is the formula for power
power= workdone/time
what are the units for power
watts
what are the units for work done
joules
what are the units for time
seconds
what is efficiency
the ratio of two energies, it has no units
what is the formula for efficiency
efficiency= useful energy (power) output/ total energy (power) input
what is the second law of thermodynamics
-energy from a heat source= useful work done + energy given to a cold sink
-Q1= W+Q2
W=Q1-Q2
what is the formula for the second law of thermodynamics
efficiency= 1 (big 1) -Q out/Q in
what is T1
temperature in (temp of the source)
what is Q1
total energy in from source
what is W
useful energy out for work done
what is T2
temperature out (temp of the sink)
what is Q2
waste product/gives out energy in the cold sink
what is the max theoretical efficiency
Q1/Q2 = T1/T2
what is COP
Coefficient Of Perfomance, it is the ratio of heat supplied to the high-temperature reservoir to work done.
what is the formula for COP
1 (BIG ONE) - Q2/Q1
what is the ideal gas
the temperature of a gas is directly proportional to the average kinetic energy of the molecules of the gas.
what is the formula for pressure
pressure= force/ area
what is the formula for kinetic energy
1/2 X mass X velocity squared
what is the formula for ideal gas
PV=NKT
pressure X volume= number of molecules in the gas X boltzmann constant X temperature
what is the Boltzmann’s constant
1.38x10-3
what is specific heat capacity
the energy needed to raise the temperature of 1kg of a substance by 1c
what does the temperature depend on if a substance is heated
- the mass of the substance
- what material the substance is made from
- the amount of energy supplied
what is the formula for specific heat capacity
delta E= M x C x delta
change in energy = mass X specific heat capacity X change in temp
what are the assumptions about ideal gas
- particles are in continuous random motion
- the volume of particles is very small compared to the volume of the gas
- particles are along way from eachother and dont interact except when they collide.
- collisions are elastic (no kinetic energy is lost during collisions)
what is an isothermal change and when does it take place
- it takes place at a constant temperature
- thermal energy can be added or released in order to keep the temperature constant
- when 2 bodies reach thermal equilibrium
when can a gas only be changed isothermally
- it is in a good conducting, thin-walled container
- it is surrounded by a constant temperature reservoir
- the change occurs very slowly
what is specific latent heat
the amount of energy needed to change the state of mass of a pure substance without changing the temperature
what is the equation for specific latent heat
Q=MxL
thermal energy= mass X specific latent heat
what is plastic deformation
when a shape/size changes and becomes permanent
what is hookes law
the extension of a spring is directly proportional to the force applied to it
what is the for hookes law
F=K x delta X
what is elastic strain energy
-when a spring is stretched potential energy is stored
what is the formula for elastic strain energy
energy= 1/2 X force X extension
what is tensile force
when a spring is stretched and made long, the spring gets deformed
what is stress
when a load is attached on a spring and it feels a pressure, the pressure is called stress
what is strain
when a load is attached on a spring the length increases, the extension of the spring is called strain
what is the formula for stress
force/ corss section area
what is the formula for strain
extension/ orgional length
what is breaking stress
the stress required to break the shape
what is young modulus
a measure of the stiffness of a material
what is the formula for young modulus
stress/ strain
what are Newtonian fluids
- the viscosity of the fluid doesn’t change with the rate of flow
- fluids are either gases or liquids
what is a adiabatic process
-no heat transfer so work input= internal energy gained
what is the kinetic theory of matter
- solids have a fixed position and but are able to vibrate
- liquids flow past each other and collide while still vibrating
- gases travel fast between collisions, atoms still vibrate and molecules can spin
what is absolute zero
where all thermal energy has been removed
all molecules are in the lowest possible energy state
what is the formula for the first law of thermodynamics
Q= delta U + W
heat in = energy change in the system + work out
what is the elastic limit
-highest tensile stress with full elastic recovery
what is ductility
the ability to be shaped by plastic flow under tension eg drawing into rods, wires or tubes
what is malleability
the ability to be shaped by plastic flow under compression eg rolling or hammering into sheets
what is ultimate tensile strength
the highest stress a material can sustain just before it breaks
what is creep
a slow version of plastic deformation, it increases with temperature
what is fatigue
caused by repeated cycles of loading and unloading which causes a crack
when does laminar/streamline flow occur
- occurs at lower values of flow rate and pressure difference
- drift of particles are all parallel and in the same sense
- velocity changes across the flow of the stream
- energy efficient
when does turbulent flow occur
- occurs at higher flow rates
- absorbs more energy as it generates more resistance to flow
- its chaotic
what is viscosity
resistance to flow
what is a Newtonian fluid
a fluid that has a constant viscosity
what is a non-Newtonian fluid
a fluid that changes its viscosity
- they change viscosity as soon as there is a shear stress
- brushing, sliding or stirring a liquid provides shear stress
what are examples of non-newtonian fluid
shear thinning (pseudoplastic) shear thickening (dilatant) fluids
what are Bingham plastics
behave like solids at low shear stresses, but above a yield stress they begin to flow
what are examples of bingham plastics
toothpaste, mud, mayonnaise
