Physics Unit 2.4 (Ch. 16-17)
solar power
Energy per unit time received from the Sun
b (bc both rods change by the same percentage)
If you have a thick, long rod and a thin, short rod and heat them both up; would you expect the short rod to get... a. 2mm longer b. less than 2 mm longer c. also 2 mm long
c
Which body glows w/ electromagnetic waves? a) Sun b) Earth c) both d) neither
radiant energy
all substances of any temperature above absolute zero emit this
convection
how liquids and gases mainly transmit heat
terrestrial radiation
name for radiant energy emitted by Earth
solar constant (is equal in power to 1.4 kilowatts per square meter)
the amount of radiation energy received each second over each square meter at right angles to the Sun's rays at the top of the atmosphere which is 1400 joules
conduction
the name for this transmission of heat: when heat enters the end of a fork that is kept in the flames and is transmitted along the entire length to your hand. The fire causes the atoms at the heated end of the fork to vibrate more rapidly. These atoms vibrate against neighboring atoms, which, in turn, do the same and free electrons that can drift throughout the metal are made to jostle and transfer energy by colliding with atoms and free electrons within the material.
-the coldest water in a lake floats -water has a high specific heat -ice has a very low thermal conductivity
3 reasons why fish can survive the winter
-any material that absorbs more than it emits is a net absorber' -any material that emits more than it absorbs is a net emitter -net absorption or emission is relative to temperature of surroundings
3 effects of surface of material on radiant energy
conduction, convection, radiation
3 ways heat gets transferred (from hotter places to colder places)
release it
A great amount of water vapor changes phase to become water in the louds that form a thunderstorm. Does this process release thermal energy or absorb it?
false (bc of specific heat capacity; water more resistant to change)
A small red-hot piece of iron is placed into a large bucket of cool water. (Ignore the heat transfer to the bucket) -true or false: the decrease in iron temperature equals the increase in water temperature
false (they both will eventually reach room temperature- has to do with outside environment and specific heat)
A small red-hot piece of iron is placed into a large bucket of cool water. (Ignore the heat transfer to the bucket) -true or false: the final temperature of the iron and water is halfway between the initial temperatures of each
true
A small red-hot piece of iron is placed into a large bucket of cool water. (Ignore the heat transfer to the bucket) -true or false: the iron and water both will eventually reach the same temperature
true (bc the law of conservation of energy states energy can only be transferred- not created or destroyed and heat's a form of energy)
A small red-hot piece of iron is placed into a large bucket of cool water. (Ignore the heat transfer to the bucket) -true or false: the quantity of heat lost by the iron equals the quantity of heat gained by the water
energy 'flows' from higher to lower temp., from your hand to the ice; it's the energy, heat, flowing from your hand that produces the sensation of coolness
If you hold one end of a piece of metal against a piece of ice, the end in your hand soon becomes cold. Dows cold flow from the ice to your hand? Explain
Air bags increase the time the force is applied and decrease the force, so the result is a lesser force for a longer duration.
In terms of impulse and momentum, why do air bags in cars reduce the risk of injury in accidents?
yes, if one has a higher temperature; internal energy doesn't matter (internal energy is like ice berg and coffee cup -> ice berg has more internal energy but if next to a coffee cup (w/ less internal energy) it would get heat from the coffee cup)
Is it possible for heat to flow between two objects with the same internal energy? Can heat flow from an object with less internal energy to one with more internal energy? Defend your answers.
bc metals are very good conductors and wood is an insulator (very bad conductor)
Many tongues have been injured by licking a piece of metal on a very cold day. Why would no harm result if a clean piece of wood
Death Valley, Sea Level, Denver
Rank the boiling- water temps from highest to lowest in these locations: Denver, Death Valley, Sea Level
heat it up
Regarding the ring and ball problem, what can you do to the ball so it can't go through the ring
yes, bc all molecules are getting heated up so it expands in every way; all would contract if got cooled down
Regarding the rod problem, would the rods also get thicker (expand in diameter)
CO2
although H2O is the major greenhouse gas in the atmosphere, the second most abundant greenhouse gas is notorious bc its contribution from humans has been steadily increasingly
absorbs
an object that emits well, also does this well
no
are most liquids and gases good conductors
a high frequency which means much of it is in the visible portion of the electromagnetic spectrum
bc the surface of the Sun has a high temperature, it emits radiant energy at this frequency
cooler (this happens at night when there's no solar radiation; an object left out in the open at night radiates energy into space, and bc space itself is extremely cold, it receives very little energy in return)
bodies that radiate more energy than they receive become...
yes
can convection occur in all fluids, whether liquids or gases
the metal (bc the metal stick conducts heat faster through conduction so heat would travel faster to the liquid nitrogen when compared to the wooden stick)
due to conduction, if you were to stick a wood stick and a metal stick in liquid nitrogen, which stick would get colder faster
no, this explanation wouldn't explain the generation of heat/energy and cold is merely the absence of heat
ex: if you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold; does cold flow from the ice to your hand?
silver, copper, gold, aluminum, iron
examples of good conductors
-heat transfer by conduction through the vacuum is impossible (some heat escapes by conduction through the glass and stopper, but this is a slow process bc glass, plastic, and cork are poor conductors) -the vacuum has no fluid to convect, so there's no heat loss through the walls by convection -heat loss by radiation is reduced by the silvered surfaces of the walls, which reflect heat wavelengths back into the bottle
explain a vacuum bottle (aka Thermos) in terms of conduction, convection, and radiation
volume also increases (and vice versa)
for most things (like steel), what happens to volume as you increase temperature
object emits white light
for radiating objects, what happens at 1500 degrees Celsius
emitters; absorbers
good absorbers are good ---; and bad emitters are bad ----
convection
heat transfer due to the actual motion of the fluid-itself
short, long
high temperature objects radiate --- wavelengths; low temperature objects radiate --- wavelengths
both freezing point and melting point are the same for a pure substance
how does the freezing point of a liquid compare w/ its melting point?
the bonding within its atomic or molecular structure
how well a metal fork or any solid object conducts heat depends on this
visible light
if an object is hot enough, some of the radiant energy it emits is
bc everything is also absorbing energy (the surface of any material, hot or cold, both absorbs and emits radiant energy)
if everything is emitting energy, why doesn't everything finally run out of it
heat from the hotter one would transfer up and then down to lower one
if you had two objects in water that are different temperatures what would happen
they will eventually reach the same temperature and heat stops flowing
if you keep two objects of different temperatures in contact, what happens
it cools down
in convection, what happens to air when you let it out of a small space into a bigger space and you let it expand
much more radiation is emitted by the hotter object than the colder object than from the colder object to the hotter object although they both emit radiation
in regards to radiation, what would happen if you had two objects that are different temperatures
no (why your hand isn't harmed if you put it briefly in a hot oven)
is air a good conductor
heat radiation (bc when the higher-frequency infrared waves are absorbed by your skin, as when you stand beside a hot stove, you feel the sensation of heat)
it's common to refer to infrared radiation as this
cool to match the surrounding temperature (the rate of cooling depends on how much hotter the object is than its surroundings)
left to themselves, objects hotter than their surroundings eventually...
radiation (radiant energy is the name used for energy that's radiated)
means why which energy is transmitted from the sun and passes through space and then through Earth's atmosphere and warms Earth's surface
heat
name for internal energy that flows from hot to cold (from a hotter object to a colder object)
infrared
name for objects w/ everyday temperatures that emit mostly low-frequency waves that are invisible to the human eye
insulators (ex: wool, wood, straw, paper, cork and Styrofoam)
name for poor conductors that impede the transfer of heat
bc the molecules all 'exited the same side of the ring bc the other of the two sides of the ring get further from each other' making the hole/center bigger
regarding the ring and ball problem, why does heating up the ring make it easier instead of harder
no, although the rate of cooling is greater for the hotter cup, it has farther to cool to reach thermal equilibrium; cooling rate and cooling time are not the same thing
since a hot cup of tea loses heat more rapidly than a lukewarm cup of tea, is it correct to say that a hot cup of tea will cool to room temperature before a lukewarm cup of tea will?
heat (and electricity)
solids composed of atoms that have one or more 'loose' outer electrons conduct this well
Newton's law of cooling (also applies to warm objects)
states the rate of cooling of an object -whether by conduction, convection or by radiation- is approximately proportional to the temperature difference between the object and its surroundings
Newton's law of cooling
states the rate of loss of heat from a warm object is proportional to the temperature difference between the object and its surroundings (similarly for the gain of heat by a cool object)
conduction
the flow of internal energy from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles (atoms, moleules, ions, electrons, etc.) in the intervening space
convection
the heat transfer due to bulk movement of molecules within fluids such as gases and liquids
when your body gets too hot, it sweats which will cool the body through evaporation
the human body can maintain its customary temp of 37 degrees C on a day when the temp is above 40 degrees C. How is this done
bad conductors (wood, wool, glass, plastic, paper)
the make good insulators bc they slow down the transfer of heat through conduction meaning things keep the same heat for longer (why you would rather step on carpet vs tile after taking a shower, bc a tile would more quickly cause heat to flow from your foot to the tile)
solar power
the rate at which solar energy is received from the Sun
the temperature difference (∆T) between the object and its surroundings
the rate of cooling of an object -whether by conduction, by convection or by radiation- is approximately proportional to...
windchill (the added convective effect of the wind)
the rate of cooling we experience on a cold day can be increased by this
radiation
the transfer of energy by means of electromagnetic waves
radiation
the transfer of energy from the Sun through empty space
convection
the transfer of heat by the circulation or movement of the heated parts of a liquid or gas.
conduction
the transfer of heat energy by molecular and electron collisions within a substance (especially a solid)
convection
the transfer of heat energy in a gas or liquid by means of currents in the heated fluid; the fluid moves, carrying energy w/ it
convection
the transfer of heat involving only bulk motion of fluids (only involves fluids)
-all things radiate, and the frequency and wavelength of radiation depend on the temperature of the object emitting the radiation (hig temp. objects radiate short wavelength and low temp. objects radiate long wavelengths) -the transparency of things such as air and glass depends on the wavelength of radiation
the two concepts associated w/ the greenhouse effect
greenhouse effect
the warming of the lower atmosphere by short-wavelength radiation from the Sun that penetrates the atmosphere, is absorbed by Earth, and is reradiated at longer wavelengths that cannot easily escape Earth's atmosphere
absorption and reflection (a good absorber of radiant energy reflects very little radiant energy, including visible light; ex. the pupil of an eye, which allows light to enter w/ almost no reflection, appears black)
these are opposite processes
metals
these have the 'loosest' outer electrons, which are free to carry energy by collisions throughout these which is why they are excellent conductions of heat and electricity
insulating
these materials that are net radiators and get colder than the air; it's common for frost to form on these kinds of materials even when the temperature of the air doesn't go down to freezing
convection currents
these stirring the atmosphere produce winds
water
this can absorb a lot of heat without changing its temperature very much due to its high specific heat capacity
temperature
this can also be known as the internal energy divided by number of molecules or particles
conduction
this form of heat transfer plays a huge role in the wind
radiant energy
this is in the form of electromagnetic waves (includes radio waves, microwaves, infrared radiation, visible light, UV radiation, X-rays and gamma rays)
heat
this is known as the internal energy 'in transit'
cold (there's no 'cold' that flows into a warm home -unless a cold wind blows into it- a home becomes colder bc heat flows out)
this is simply the absence of heat
weather; climate
this is the state of the atmosphere at a particular time and place- its temperature, humidity, pressure, precipitation, wind and clouds; this is the weather pattern over broader regions and longer times
convection
this is what causes, what causes hot water (or air) to rise and cold water (or air) to sink like when boiling a pot of water
convection
this is why if you have air in a large room and you warm it up it will expand but if you have air in a small container and you let it out in a big room and let it expand, it will cool
conduction
this is why you can cool a burned finger after you touch something hot by closing your lips which increases pressure and makes the air that comes out of your mouth expand and cool but in order to warm up your hands, you blow on them with your mouth open wider which makes the air that comes out warmer
an insulator (ex: even the best-insulated warm homes in winter will gradually cool; insulations slows heat transfer)
this merely reduces the rate at which heat penetrates
absorption of radiant energy
this occurs along w/ emission of radiant energy
convection
this occurs wherever fluids are subjected to temperature differences (ex: it produces clouds in the sky and contributes to ocean currents in deep ocean waters)
conduction
type of heat transfer that involves the collision of particles (could be from a gas in air, could be electrons in a metal, etc.)
convection
unlike conduction (in which heat is transferred by successive collisions of electrons and atoms), this involves the motion of 'blobs' of matter- the overall movement of molecules of a fluid
high to low
w/ conduction, heat travels from...
rises; sinks
w/ convection, hot water ---- while cool water ----
the temperature difference between the object and its surroundings (also applies to warm objects)
what Newton's law of cooling states the rate of cooling of an object -whether by conduction, convection, or by radiation- is approximately proportional to this
yellow light is emitted
what happens to radiating objects at about 600 degrees Celsius
red light is emitted, longest waves visible
what happens to radiating objects at temperature above 500 degrees Celsius
they form hexagons and it starts to expand (something expanding as you cool it happens to almost nothing except water; this pretty much only happens in 0-4 degrees Celsius temperature range)
what happens when you freeze water molecules and cool it between 0-4 degrees Celsius
the absolute temperature of the source
what the frequency of radiation is proportional to
the difference in temperature between objects (if you have two objects - one colder and one hotter they will eventually reach the same temperature however they will continue to radiate and emit)
what the rate of heat flow from hot to cold is proportional to
radiation
what the surface of Earth losing energy to outer space is due to
the frequency of radiation which is the rate of vibration of a wave
what the wavelength of radiation is related to
greenhouse effect
what this is an ex. of: a car parked in the street in the bright Sun on a hot day with closed windows can get very hot inside- appreciably hotter than the outside air
convection
what this is an ex. of: the visible shimmer of air above a hot stove or above asphalt on a hot day; visible shimmers in water due to temperature difference
it would cool (air in opening of balloon- small space- going into big space like a room which makes it expand and so it would cool)
what would happen if you were to open a balloon by slowly untying it
it would expand and freeze bc the carbonated water would turn to ice
what would happen to a can of soda if you were to freeze it
their temperatures are the same
when you press a hot and cold object together, the hot object transfers heat to the cold object until...
the water evaporates quickly in the dry air and gains its energy from your skin, which is cooled
when you step out of a swimming pool on a hot, dry day in the Southwest you feel quite chilly. Why?
dirty snow bc it's darker than the clean snow (which would reflect more)
which melts faster in sunshine- dirty snow or clean snow
compared w/ the car, the Sun's temperature is very high which means the wavelenth radiated by the Sun are very short and these short wavelengths easily pass through both Earth's atmosphere and the glass windows of the car
why a car gets so hot in bright sunlight
bc there's less air pressure which means it takes less energy to bring water to the boiling point
why does the boiling temp of water decrease when the water is under reduced pressure, such as when it's at a higher altitude
bc steam contains more energy
why is a steam burn more damaging than a boiling water burn at the same temp?
it's a good insulator and therefore poor conductor of heat (so you can grasp the wooden handle of a pot and quickly move it w/o getting burned)
why wood is used in the handles of cookware
no, bc there's no energy transfer between the fur coat and the thermometer
wrap a fur coat around a thermometer, will its temp rise?
solar constant
1400 J/m^2 received from the Sun each second at the top of Earth's atmosphere on an area perpendicular to the Sun's rays; expressed in terms of power, 1.4 kW/m^2
change in length (either shorter or longer)
(like the long and short rod problem), the longer an object is and the greater the change in temperature, the greater the...
radiation
Which means of heat transfer don't require any medium at all
yes
can ice be colder than 0 degrees?
infrared
for radiating objects, room temperature emission is in the...
terrestrial radiation
the radiation emitted by Earth to outer space
