Unit 5- Lecture 3

Temperatureis a measure of the average kinetic energy of

the particles in the object.based on the motion of the particles in a

substancefast motion = high temperatureslower motion = lower temperature

Temperaturerelatively describes how the particles collide

with the surface of the thermometercollisions transfer energy

measured in K (kelvin) in SI systemno degrees mark, same size divisions as

Celcius

Temperature ScalesFahrenheit

Common in the USFreezing point of water is 32ºFBoiling point of water is 212ºF

CelsiusCommon in the rest of the world (SI)Freezing point of water is 0ºCBoiling point of water is 100ºC

Temperature ScalesKelvin

used for science, as there are NO negative values

0 K is set at Absolute Zero, the temperature at which all particle motion stops

Freezing point of water is 273KBoiling point of water is 373K

NOTE – 100 K between freezing and boiling, so Kelvin uses the same degrees as Celsius

Converting TemperaturesFahrenheit to Celsius

Cº = (5/9) * (Fº - 32º)Celsius to Fahrenheit

Fº = (9/5) * ºC + 32Celsius to Kelvin

K = ºC + 273

Adjusts for differences in Zero temperature

Heatis a flow of energy from objects of higher

thermal energy to objects of lower thermal energy

heat is measured in Joules (J) because it is a form of energy

described as a flow from hot to coldno such thing as “cold”

Specific Heatamount of energy needed to raise

1 kg of something by 1 ºCmeasured in:

joules per kilogram degree CelciusJ / (kg * ºC)

is measured using a calorimeterrepresented by the variable “Cp”

Specific Heatnote: water has an incredibly high specific

heat value due to the bonds between water molecules

this is why water is used as a coolant – because it will absorb a lot more energy before its temperature increases

Thermal Energysum of the potential and kinetic

energy of the object’s particlesmore particles more mass

more thermal energyrelationship: inverse / direct?

faster moving greater temperature more kinetic energy more thermal energyrelationship: inverse / direct?

Thermal Energychanges in thermal energy :

mass * change in temperature * specific heat

kg * ºC * (J / [kg * ºC])Q = m * C * (Tf - Ti)Q = m * C * ∆T

Because heat is a form of energy, heat is measured in …

1. Watts2. Newtons3. Joules4. Mishbohah

Heat always flows…1. From low E to high E2. From high E to low E3. Across layers of density4. Downwards, like gravity

The average motion of particles in a substance defines that substance’s…

1. Heat2. Energy3. Potential Energy4. Temperature

The temperature scale used in the USA is1. Fahrenheit2. Celsius3. Kelvin4. Thermocline

The temperature scale used in SI is1. Fahrenheit2. Celsius3. Kelvin4. Thermocline

The temperature scale used in science is1. Fahrenheit2. Celsius3. Kelvin4. Thermocline

Thermal Expansionas substances increase in temperature,

the particles move apartsubstances expand and

become less dense when heatedsubstances shrink and

become more dense when cooledexplains expansion joints in

bridges and concrete sidewalkswater is one very important exception

Examples of Thermal ExpansionNotice the cracks

that have formed in the concrete after some time of thermal expansion

Transferring Thermal Energyconduction – transfer by DIRECT particle

contactheat [and electricity] moves faster in solids

[to heat or cool]little to no

resistance low specific heatbest are metals

because of “sea of electrons” that move between elements

Transferring Thermal Energyinsulators

resist the flow of heat [& electricity]high specific heatresisted heat builds

up and can cause substance to burn

typically non-metalslarge molecules,

no free electrons

Transferring Thermal Energyconvection – transfer by mass movement of

particlestransfer by fluid movement between warmer

and cooler locationscurrents:

warm expands [higher – less dense],

cold contracts [lower – more dense]

Transferring Thermal EnergyRadiation – transfer by invisible radiation

electromagnetic wavesfrequently called

radiant energy

More on RadiationEmitters are substances that give off

radiationstars, campfires, space heaters, etc.

Absorbers capture radiationblack shirts, asphalt, water

Reflectors return most of the radiation that is emitted towards themmirrors, aluminum foil, ice & snow

Layers and Heat TransferLayers trap air in a “dead air space”More layers mean it’s harder to change

temperatures between layersEx. double-paned windows, dressing in

layers, layers of construction on a house

What type of heat transfer describes cooking on an electric range?

1. Conduction2. Convection3. Radiation

What type of heat transfer describes why a dark shirt feels warmer on sunny days?

1. Conduction2. Convection3. Radiation

What type of heat transfer describes how a A/C system changes room temperature?

1. Conduction2. Convection3. Radiation

What type of heat transfer describes how lake water is hot on top and cold on bottom?

1. Conduction2. Convection3. Radiation

What type of heat transfer describes cooking in an electric oven?

1. Conduction2. Convection3. Radiation

HomeworkIf you’re not working well…

you [individuals] will have an additional assignment

If assigned and completed correctly, no penalty, no benefit

If assigned and not completed correctly, will be – 15pts to your current accuracy score.Pg. 163 – Questions # 1- 4Pg. 170 – Questions # 1 – 4

Homework If you’re working well….complete onlyHeat Calculations w/sTemperature conversions w/s