Unit 28 - Heat And Temperature
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Transcript of Unit 28 - Heat And Temperature
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 ThomsonBaron 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°F298 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
ConductionWhen 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.
Lava Lamps are an example of convection that you have probably seen before.
Convection con’t
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
Radiation
• 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