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 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