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

Thermal ExpansionThermal 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 ExpansionExamples 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, free electrons

InsulatorsInsulators

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

• Resisted heat can build up and cause the substance to burn

• Usually nonmetals• Large molecules, no free electrons

Heat TransferHeat Transfer

• Conduction• HTB direct particle contact

• Convection• HTB mass movement of particles

• Radiation• HTB invisible infrared radiation

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

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

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)

Homework 26Homework 26

• Pg. 163 – Questions # 1- 4• Pg. 170 – Questions # 1 - 4

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

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