Thermal physics; lecture 6-7 Flashcards
When does a phase change occur?
when the heat added to a substance increases the temperature of the substance enough that, it reaches a temperature that is characteristic for a phase change
how does evaporation cool our body
water on our skin absorbs body heat, as evaporation cools the body
How does condensation occur
gas to liquid
- gas molecules near a liquid surface are attracted to the liquid; they strike the surface with increased KE becoming part of the liquid
true or false; if enough energy is supplied to a vapor the molecules or atoms will disintegrate into ions and electrons, form plasma of charged particles = 4th phase of matter!!
true (WOW)
What is boiling
rapid evaporation from beneath the surface of a liquid; forms vapor bubbles beneath the surface
What are the conditions of boiling
- pressure
- altitude (boiling point is lower with lower atmospheric pressure)
Define latent heat
the heat needed for 1 kg of substance to undergo phase change
What does latent heat depend on
the material, also on the phase change about to occur on the substance
latent heat of fusion
phase change from solid to liquid
latent heat of vaporisation
liquid to gas
What does heat of fusion mean?
amount of energy needed to change any substance from solid to liquid
heat fusion of water 344 J/g
define heat of vaporization
amount of energy needed to change any substance from liquid to gas; and vice versa
What is the only stress that can be exerted on an object submerged in a static fluid
is the one that tends to compress the object from all sides
true or false; the force exerted by a static fluid on an object is always perpendicular to the surfaces of the object
true
what causes atmospheric pressure
- caused by weight of air
- varies from one locality to another
- not uniform
- measurements are used to predict weather conditions
What is the barometer
it is a device used to measure atmospheric pressure
- it consists of a mercury tube, upside down and a dish filled with mercury; the height of the mercury column tells us the atmospheric pressure
What is an aneroid barometer
- partially exhausted metal box of air with a flexible
- lid bends in and out with changes in atmospheric pressure
- the motion of the lid is indicated on a scale
what measures elevation
altmeter
what is a manometer
- a device used to measure the pressure of a gas contained in a vessel
what does buoyant force mean
the upward force exerted by the fluid on any immersed object
- the buoyant force is the resultant force due to all forces applied by the fluid of surrounding the parcel
buoyancy in air
archimedes principle: states that an object surrounded by air is buoyed up by a force equal to the weight of displaced air
object lighter than air (rise or fall)
rise
when does an object hover
weight of air displaced = the weight of the object
When does a balloon stop rising
when the weight of the displaced air equals the total weight of the balloon
- the buoyant force on the balloon equals its weight
what are the foundations of thermodynamics
conservation of energy
the fact that heat flows from hot to cold and not the other way round
true or false; at zero degrees with pressure constant, volume changes by 1/273 for each degree celsius
true
what is absolute zero
when molecules have lost available kinetic energy
what is internal energy
energy at the particle level within a substance in several forms
- simplest form is PE and KE
if the gas expands (+ or - work)
the work done is positive
if the volume compresses (work? + -)
negative
volume remains constant
w= 0
What does the first law of thermodynamics take into account
heat and work
what does the first law of thermodynamics state?
the heat added to system transforms into an equal amount of some other form of energy
what is an isolated system
one that does not interact with its surroundings
- no energy transfer by heat takes place
- the work done on the system is zero
the internal energy remains constant
What is an adiabatic process
compressing or expanding gas while no heat enters or leaves the system
how is adiabatic conditions achieved
- thermally insulated system from its surroundings
- performing the process so rapidly that heat has no time to enter or leave change in e internal = work
true or false if the gas expands adiabatically, work is negative
true
if gas is compressed adiabatically, work done is positive
true
true or false; when an object floats; the fraction of the volume of floating object that is below the fluid surface is equal to the ratio of the density of the object to that fluid
true
What is absolute temperature based on
triple point
absolute zero
