c1 Flashcards
(30 cards)
what is the unit for young modulus
Nm-2
which property allows steel to be drawn into a wire
ductility
which physical property measures the resistance to flow in a fluid
viscosity
as the car is passing the lorry the air flow moves the car towards the lorry. explaih why the air flow noves the car towards the lorry
• air flow between the lorry and the car is faster
• air is moving in the opposite direction of the vehicle
• air pressure is decreasing between lorry and the car
• therefore a pressure difference is formed which produces an inward force pulling the vehicle together
compare similarites and differences of the elastic and plastic properties of the two materials (steel wire & polythene bag)
• steel wire is malleable so can maintain shape and is stronger
• polythene bag undergos elastic deformation therefore cannot return to original shape once deformed
• both have an elastic section
• both store elastic potential energy that can be released on uloading
hookes law applies to elastic regions of both materials
amount of pressure exerted by the gas depends on:
• volume of the container
• the number of gas particles - moles
• temperature of gas
ideal gas equation =
pv = nRT
what energy transfers are involved in a heating pan of boiling water and why does the temperature of the water not increase
because its an isothermal process the temp of system remains constant
• heat energy is transferred from the fire to the boiling water
• some water molecules are vapourised from liquid into gas which requires energy
• energy supplied by the fire is equal to energy used to vapourise the water molecules
• overall the internal energy of the liquid does not change
• because ^U = O, because ^U = Q -W which rearranges to Q = W
aerosols become cold when sprayed why does this happen
no heat is transferred to or from the system. using aerosol is example of adiabatic gas expansion
• expanding aerosol gas works by pushing away the surrounding air
• this requires energy which comes from the internal energy of the aerosol gas
• so aerosol becomes cold when it releases gas
why is this adiabatic?
• no heat was transferred to or from the can to make this process happen
• the only energy transferred was due to the aerosol doing work on the surrounding air because Q = O, ^U = Q-W becomes ^U = -W always negative so temp of gas will decrease
1st law of thermodynamics =
sum of all the energy particles in a system is called internal energy and given the symbol U
2nd law of thermodynamics =
heat energy never flows spotaneously from a colder object to a hotter object, heat energy always goes from a hotter object to colder.
hand = hotter ice = colder
fire = hotter hand = colder
heat pumps and refrigerator and effciency of a fridge
compressor:
• to compress the coolant vapour when it heats up
condenser coils:
• to remove heat energy from the coolant and transfer it to surroundings via conduction + R
• metal coils aid C
• painter black which aids R
• changes from vapour to liquid
expansion device:
• liquid coolant expands and some becomes a vapour, which decreases the temp
• expansion = adiabatic process
evaporator coils:
• to remove heat energy from the fridge by transferring it to the coolant
• energy transferred to the coolant causes it to evaporate and become vapour
effciency of a fridge
compressor
~ it heats up when condensing vapour which wastes energy and overall energy
condenser coils
~ effciency of cooling and condensing vapour depends on the differnce in temp between the cooler and the surroundings
~ not all heat/energy can be removed from coolant
expansion device
~ almost 100% effcient
evaporator coils
~ effciency of cooling inside the fridge depends on how fast heat can be extracted from the fridge
state one property of modelling clay that shows it is a plastic material
keeps its shape
which property allows copper to be hammered into shape
malleability
which physical property describes the way some solid materials move slowly and deform permanently with time
creep
describe heat engines and how they work
opposite if refrigerators and heat pumps they are devices that use the spotaneous transfer of heat energy from hotter objects to colder objects and convert it to mechanical energy to do work
explain the effciency of heat engines
energy effciency measures the proportion of energy which is wasted. this is an important thing to measure and often see stickers on electrical appliances which show how effcient they are.
describe the process of petrol engines
1) intake = fuel and air mixture is taken into the piston
2) compression = piston compresses the mixture adiabatically and volume of the mixture decreases and pressure increases
3) ignition = the mixture is ignited and this causes an increase in temperature and pressure with no change in vol
4) expansion = the gas expands adiabatically and works to push the piston out and volume of gas increases and pressure decreases
5) exhaust = the piston is open which decreases the pressure with no change in volume and the gas leaves the piston
describe the state of ice
• molecules are close together
• molecules vibrate in a fixed position
• strong IMF between molecules
describe water as a state
• molecules are quite close together
• molecules can move by sliding past eachother
• IMF are weaker than ice but stronger than steam
describe steam as a state
• molecules are far apart
• molecules are able to move freely
• almost no IMF between molecules
melting bouling condensing and freezing
solid to liquid = melting
liquid to gas = boiling
gas to liquid = condensation
liquid to solid = freezing
describe the energy of the molecules in each state
• the more energy = the higher temp
• molecules in solid water have least kinetic energy
• molecules in steam gas have most kinetic energy
