HeatHeat

The Fire Down Below

HeatHeat

• 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”

TemperatureTemperature

• Based on the motion of the particles in a substance• Fast motion = high temperature• Slower motion = lower temperature

• Relatively describes how the particles collide with the surface of the thermometer• Collisions transfer energy

Temperature ScalesTemperature 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 ScalesTemperature Scales

• Kelvin• Used for science, as there are NO negative

values• 0K 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 – 100K between freezing and boiling, so Kelvin uses the same degrees as Celsius

Converting TemperaturesConverting Temperatures

• Fahrenheit to Celsius

Cº = 0.55 (Fº - 32º)• Celsius to Fahrenheit

Fº = (1.8 x Cº) + 32º

• Celsius to Kelvin

K = C + 273

Adjusts for differences in Zero temperature

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

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

1. Watts

2. Newtons

3. Joules

4. Mishbohah

Heat always flows…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…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 isThe temperature scale used in the USA is

1. Fahrenheit

2. Celsius

3. Kelvin

4. Thermocline

The temperature scale used in SI isThe temperature scale used in SI is

1. Fahrenheit

2. Celsius

3. Kelvin

4. Thermocline

The temperature scale used in science isThe temperature scale used in science is

1. Fahrenheit

2. Celsius

3. Kelvin

4. Thermocline

Thermal EnergyThermal Energy

• Usually based on the total number of particles, as most temperatures in which we survive are relatively close together (-15ºF to 130ºF)• More particles = more thermal energy

• Ex. boiling cabbage, frying foods, ocean water

Heat TransferHeat Transfer

• Conduction• HTB direct particle contact

• Convection• HTB mass movement of particles

• Radiation• HTB invisible infrared radiation

ConductionConduction

• Heat transfer by direct particle contact• The particles of the higher energy material

vibrate more rapidly• As they collide with the lower energy material,

some of the particles increase speed• Eventually, all the particles vibrate at the same

speed• Mix hotter and colder materials? The temperature

moderates…

More on conduction…More on conduction…

ConvectionConvection

• Heat transfer by mass particle movement• The particles of the higher energy material

vibrate more rapidly, and• Thermal expansion causes the particles of the

hotter material to become less dense• The warmer, less dense material rises,• The cooler, more dense material sinks

Above and Below…Above and Below…

• Inside the Earth, heat from Earth’s core moves towards the surface through the plastic mantle

Above and Below…Above and Below…

• The atmosphere and hydrosphere move heat through convection in weather and ocean currents

RadiationRadiation

• Heat transfer by invisible, electromagnetic waves• Infrared waves are given off because of particle

motion or electrons changing energy levels during reactions

• The waves released can be absorbed by other particles, interpreted as heat

Feel the heat!Feel the heat!

• The Earth is warmed by infrared radiation from the Sun

• NO HEAT IS RECEIVED FROM THE SUN BY DIRECT PARTICLE CONTACT

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

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?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?

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?

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?

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

1. Conduction

2. Convection

3. Radiation

Thermos bottles…Thermos bottles…

• Reduce heat flow in BOTH directions

• Vacuum eliminates convection, conduction

• Inner bottle is usually reflective to reduce radiation

Specific HeatSpecific Heat

• Amount of energy that has to be lost or gained by a substance to change temperature

• Note: Water has an incredibly high specific heat value due to the bonds between water molecules• Ammonia has a higher specific heat, but you

can’t use it to cook!

Specific HeatSpecific Heat

Q = m c T

where m is the mass of the substance

c is the specific heat value

T is the change in temperature of the substance (Tfinal – Tinitial)

More on RadiationMore 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

Thermal ExpansionThermal Expansion

• As substances increase in temperature, the particles move apart• Essentially Charles’s Law:

• As temperature increases, volume increases• As temperature decreases, volume decreases

• Substances expand and become less dense when heated

• Substances shrink and become more dense when cooled

Thermal ExpansionThermal Expansion

• Explains expansion joints in bridges and concrete sidewalks

• Water is one very important exception• As liquid water freezes to become ice, the water

molecules arrange in to a lattice with air spaces• ICE FLOATS BECAUSE IT IS LESS DENSE• Density of liquid water = 1g/cm3

• Density of ice = 0.92 g/cm3

Examples of Thermal

Expansion

Examples of Thermal

Expansion• Notice the cracks that

have formed in the concrete after some time of thermal expansion

ConductorsConductors

• Allows heat (and electricity) to flow easily with little or no resistance

• Heats up quickly, cools down quickly• Low “Specific Heat”

• Usually metals• High density (no air spaces), free electrons

InsulatorsInsulators

• Resist the flow of heat (and electricity)• High “Specific Heat”

• Designed to trap “dead air” spaces• Resisted heat can build up and cause the

substance to burn• Usually nonmetals

• Large molecules, no free electrons

Layers and Heat TransferLayers 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

Combining insulationCombining insulation

• Notice the pipes wrapped in “fluffy” insulation, but the outside is shiny.

• The “fluffy” traps “dead air” spaces where the shiny inhibits radiation

Why are gaps designed in bridges, roads and sidewalks?

Why are gaps designed in bridges, roads and sidewalks?

1. As temperatures drop, the materials contract

2. As temperatures rise, the materials expand

3. To save money on the project by reducing the amount of materials

4. None of the above

Which type of heat transfer is impeded by reflective materials ?

Which type of heat transfer is impeded by reflective materials ?

1. Convection

2. Conduction

3. Radiation

4. None of the above

Which type of window would be the best insulator for your home?

Which type of window would be the best insulator for your home?

1. Single-paned

2. Double-paned

3. Triple-paned

4. Wooden shutters

Which type of heat transfer is impeded by materials that trap “dead air” spaces ?Which type of heat transfer is impeded

by materials that trap “dead air” spaces ?

1. Convection

2. Conduction

3. Radiation

4. None of the above

Which type of heat transfer is impeded by vacuums and gaps in designs ?

Which type of heat transfer is impeded by vacuums and gaps in designs ?

1. Convection

2. Conduction

3. Radiation

4. None of the above

Explain these…Explain these…

• Why was the Amundsen-Scott Antarctic Station is built to be half under the ice?

• Why do desert-dwelling peoples wear a dark outer layer on top of their inner layers?

Explain these…Explain these…

• Why would a hunter “dress in layers” the way your parents always suggest?

• What can you infer about the parts of the roof of this house that have no snow?