Unit 5- Lecture 3

Temperature is a measure of the average kinetic energy of the particles in the object. based on the motion of the particles in a substance fast motion = high temperature slower motion = lower temperature

Temperature relatively describes how the particles collide with the surface of the thermometer collisions transfer energy measured in K (kelvin) in SI system no degrees mark, same size divisions as Celcius

Temperature Scales Fahrenheit Common in the US Freezing point of water is 32ºF Boiling point of water is 212ºF Celsius Common in the rest of the world (SI) Freezing point of water is 0ºC Boiling point of water is 100ºC

Temperature Scales Kelvin 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 273K Boiling point of water is 373K NOTE – 100 K between freezing and boiling, so Kelvin uses the same degrees as Celsius

Converting Temperatures Fahrenheit to Celsius Cº = (5/9) * (F º - 32 º ) Celsius to Fahrenheit Fº = (9/5) * º C + 32 Celsius to Kelvin K = º C Adjusts for differences in Zero temperature

Heat is 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 cold no such thing as “cold”

Specific Heat amount of energy needed to raise 1 kg of something by 1 º C measured in: joules per kilogram degree Celcius J / (kg * º C) is measured using a calorimeter represented by the variable “C p ”

Specific Heat note: 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 Energy sum of the potential and kinetic energy of the object’s particles more particles  more mass  more thermal energy relationship: inverse / direct? faster moving  greater temperature  more kinetic energy  more thermal energy relationship: inverse / direct?

Thermal Energy changes in thermal energy : mass * change in temperature * specific heat kg * º C * (J / [kg * º C]) Q = m * C * (T f - T i ) Q = m * C * ∆T

Because heat is a form of energy, heat is measured in … 1. Watts 2. Newtons 3. Joules 4. Mishbohah

Heat always flows… 1. From low E to high E 2. From high E to low E 3. Across layers of density 4. Downwards, like gravity

The average motion of particles in a substance defines that substance’s… 1. Heat 2. Energy 3. Potential Energy 4. Temperature

The temperature scale used in the USA is 1. Fahrenheit 2. Celsius 3. Kelvin 4. Thermocline

The temperature scale used in SI is 1. Fahrenheit 2. Celsius 3. Kelvin 4. Thermocline

The temperature scale used in science is 1. Fahrenheit 2. Celsius 3. Kelvin 4. Thermocline

Thermal Expansion as substances increase in temperature, the particles move apart substances expand and become less dense when heated substances shrink and become more dense when cooled explains expansion joints in bridges and concrete sidewalks water is one very important exception

Examples of Thermal Expansion Notice the cracks that have formed in the concrete after some time of thermal expansion

Transferring Thermal Energy conduction – transfer by DIRECT particle contact heat [and electricity] moves faster in solids [to heat or cool] little to no resistance low specific heat best are metals because of “sea of electrons” that move between elements

Transferring Thermal Energy insulators resist the flow of heat [& electricity] high specific heat resisted heat builds up and can cause substance to burn typically non-metals large molecules, no free electrons

Transferring Thermal Energy convection – transfer by mass movement of particles transfer by fluid movement between warmer and cooler locations currents: warm expands [higher – less dense], cold contracts [lower – more dense]

Transferring Thermal Energy Radiation – transfer by invisible radiation electromagnetic waves frequently called radiant energy

More on Radiation Emitters are substances that give off radiation stars, campfires, space heaters, etc. Absorbers capture radiation black shirts, asphalt, water Reflectors return most of the radiation that is emitted towards them mirrors, aluminum foil, ice & snow

Layers and Heat Transfer Layers trap air in a “dead air space” More layers mean it’s harder to change temperatures between layers Ex. double-paned windows, dressing in layers, layers of construction on a house

What type of heat transfer describes cooking on an electric range? 1. Conduction 2. Convection 3. Radiation

What type of heat transfer describes why a dark shirt feels warmer on sunny days? 1. Conduction 2. Convection 3. Radiation

What type of heat transfer describes how a A/C system changes room temperature? 1. Conduction 2. Convection 3. Radiation

What type of heat transfer describes how lake water is hot on top and cold on bottom? 1. Conduction 2. Convection 3. Radiation

What type of heat transfer describes cooking in an electric oven? 1. Conduction 2. Convection 3. Radiation

Homework If 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- 4 Pg. 170 – Questions # 1 – 4

Homework If you’re working well….complete only Heat Calculations w/s Temperature conversions w/s