Heat

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# Heat - PowerPoint PPT Presentation

Heat. The Fire Down Below. Heat. 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”. Temperature.

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## PowerPoint Slideshow about ' Heat' - walter-hebert

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### Heat

The Fire Down Below

Heat
• 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”
Temperature
• 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 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
• 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 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

Heat always flows…
• From low E to high E
• From high E to low E
• Across layers of density
• Downwards, like gravity
• Heat
• Energy
• Potential Energy
• Temperature
The temperature scale used in the USA is
• Fahrenheit
• Celsius
• Kelvin
• Thermocline
The temperature scale used in SI is
• Fahrenheit
• Celsius
• Kelvin
• Thermocline
The temperature scale used in science is
• Fahrenheit
• Celsius
• Kelvin
• Thermocline
Thermal 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 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
Conductors
• 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
Insulators
• 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 Transfer
• Conduction
• HTB direct particle contact
• Convection
• HTB mass movement of particles
• Conduction
• Convection
What type of heat transfer describes why a dark shirt feels warmer on sunny days?
• Conduction
• Convection
What type of heat transfer describes how a A/C system changes room temperature?
• Conduction
• Convection
What type of heat transfer describes how lake water is hot on top and cold on bottom?
• Conduction
• Convection
• Conduction
• Convection
Specific 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 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 26
• Pg. 163 – Questions # 1- 4
• Pg. 170 – Questions # 1 - 4
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