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# Unit 28 - Heat And Temperature

## on Jan 26, 2010

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Heat and Temperature

Heat and Temperature

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## Unit 28 - Heat And TemperaturePresentation Transcript

• Heat and Temperature
Unit 28
• Temperature
Temperature is a measure of the average Kinetic Energy of the particles in a substance.
Remember KE is the energy of motion.
The higher the average Kinetic Energy, the faster the particles move
Temperature and Heat are NOT the same thing
View these sites for more on temperature
Temperature and Temperature Scales
Temperature
• Temperature Scales
There are 3 Types of Temperature Scales
Fahrenheit
Celsius
Kelvin
Celsius Fahrenheit
• Fahrenheit Scale
Most commonly used in United States. (originated in Great Britain)
Non-metric system scale
Not usually used in science
Visit these “cool” web sites
Converting between oF and oC
Fahrenheit and Celsius Scales
History of Fahrenheit Scale
• How Fahrenheit Works
Water freezes at 32°F
Water boils at 212°F
Zero was based on the lowest they could get water to stay liquid at the time
(with salt in it).
100° was based on the highest it was believed humans could survive at the time
• Celsius Scale
Based on Metric System Scale
Most used in the world, including Canada, Europe, and Asia
Visit these “cool” web sites
History of Celsius Scale
Converting between oF and oC
Anders Celsius
• How Celsius Works
Water freezes at 0°C
Water boils at 100°F
Absolute zero is -273°C
• Kelvin Scale
Actual Metric System scale.
Most often used in Laboratory settings for calculation purposes.
There are no negative temperatures.
A change (Δ) of 1oC = 1 K.
Converting from oC to K
William Thomson
Baron of Kelvin
• Absolute Zero
Defined as 0 Kelvin.
Average temperature of space is 2.7K
Scientists have gotten within fractions of absolute zero, but it is impossible to ever completely stop the movement of an atom, since that means it has zero energy.
Boomerang Nebula contains the coldest known temperature in the universe at 1K
Helium can only become a gas at below 5K
• Temperature Scale Comparisons
373 K = 100°C
37°C = 99°F
298 K = 25°C
273 K = 0°C
-40°C = -40°F
0 K = -273°C
• Heat Transfer
Conduction, Convection, and Radiation
• Types of Heat Transfer
• Conduction
Takes place between solids or solids with liquids
Particles vibrating or moving faster transfer some of their energy to nearby atoms
• Conduction
When particles collide and the faster ones pass some of their energy on to the cooler ones.
This results in a change in energy for each particle
This causes the faster ones to slow down and cool
The slower ones speed up and heat up
• Examples of Conduction
Conduction requires direct contact
• Convection
Occurs in Fluids (liquids and gases)
Caused by a change in density due to a change in temperature.
• Convection con’t
The warmer fluid expands, becomes less dense and rises.
The cooler fluid contracts, becomes more dense and sinks.
• Convection con’t
Lava Lamps are an example of convection that you have probably seen before.
• Importance of Convection
Convection causes warm water vapor to rise, condense into clouds when it cools,
and then falls back as rain
Without convection, there would be no rainfall and thus no plants
• Examples of Convection
Magma in the mantle rises due to convection.
The heat from the core heats it and then it rises to form volcanoes on the surface
The transfer of energy due to Infrared and other electromagnetic rays.
Radiation can travel through space.
All things radiate heat.
• Why are light bulbs hot?
They produce infrared radiation in addition to visible light
Infrared transfers energy to the molecules that makes them vibrate faster (thus hotter)
• Thermal Expansion
When objects heat up their particles move faster, hit others harder, and bounce further, creating more empty space between the particles.
As a result, the entire substance expands.
This is known as thermal expansion
• Examples of Thermal Expansion
Roads crack as they expand in the heat
On bridges and other sensitive sections, expansion panels allow it to flex.
• Thermal Expansion continued
The liquid in a thermometer expands as it warms.
This causes it to head up the tube and tell you the temperature
• Heat Transfer
Heat Conductors
Good thermal conductors transfer heat rapidly
Metals are good thermal conductors
Radiators are metals that transfer the heat in the water to the air
Frying pans transfer heat from the stove to the food
• Heat Transfer
Thermal Insulators
Poor thermal conductors of heat.
Asbestos, cork, ceramic, cardboard, and fiberglass are examples of thermal insulators