What is Heat Ch 10.2 8th

8/14/2019 What is Heat Ch 10.2 8th

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WHAT IS HEAT?

Chapter 10 Section 2


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Objectives:

Define heat as thermal energy transferred

between objects at different temperatures

Compare conduction, convection, and

radiation

Use specific heat capacity to calculate heat


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Section vocabulary:

Heat

Thermal energy

Thermal conduction

Thermal conductor Thermal insulator

Convection

Radiation

Specific heat


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Transferred Thermal Energy:

Heat: the energy transferred between objects

that are at different temperatures

Why do some objects feel hot and others

cold??

When 2 objects come in contact, heat istransferred from the highertemp to the lower

temp object


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Reaching the Same

Temperature:

Objects in contact, energy is transferred from

the warmer object to the colder object

When objects have the same temperature

there is no net change in thermal energy

One object may have more thermal energythan the other, both objects are at the same

temperature


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Energy Transfer:

http://resources.edb.gov.hk/cphysics/heat/tep/trans/heat_transfer.gif


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Conduction, Convection, &

Radiation:

3 Ways to transfer thermal energy:

http://4.bp.blogspot.com/_yHkXsgfstqE/Suzu5YuQkBI/AAAAAAAAAGM/0eorThn-bZA/s400/heat-transmittance-

means.jpg


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Conduction & Insulators:

Thermal conductors: substances that conduct

thermal energy very wellExample: doctors metal in a stethoscope

Thermal insulators: substance that do not

conduct thermal energy well

Example: doctors wooden tongue depressor

*Table in text pg. 283


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Convection:

Convection: the transfer of thermal energy by

the movement of a liquid or a gas

Circular patterns of convection due to

differences in density (convection currents)

Warmer water rises, cooler water sinks


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Convection:

http://upload.wikimedia.org/wikipedia/commons/0/08/Convection.gif


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Radiation: Radiation: the transfer of energy by

electromagnetic waves (ex: visible light, infraredwaves)

Energy transferbetween particles OR acrossempty space

Sun emits visible light you can see and infraredand UV waves you cannot see

Yourbody absorbs infrared waves which can befelt as heat


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Radiation:

http://www.wyckoffschools.org/eisenhower/teachers/chen/images/3-14.jpg http://www.valorfireplaces.com/_img/education/radiantheat.j

pg


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Radiation & the Greenhouse

Effect: The Earths atmosphere traps heat energy like

a greenhouse

Greenhouse gases: water vapor, carbon

dioxide, methane

Too many trapped gases may make the Earthtoo warm


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Heat & Temperature Change Thermal Conductivity: the rate at which a

substance conducts thermal energy

Example: Your seatbelt metal buckle has a

higher thermal conductivity; the cloth does notconduct heat well. They are both the same

temperature, the metal feels hotter!


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Specific Heat: Most metals have very low specific heat

Waterhas a very high specific heat

Substance Specific Heat(J/kgC)

Metal of seatbelt 500

Cloth of seatbelt 1,3

40Water 4,184


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Heat, Temperature, & Amount: Energy must be calculated, it cannot be

measured directly

Heat (amount of energy) is measured in joules

(J)

How much energy is needed to heat a cup of

water to make tea?

Must consider the waters mass, temperaturechan e, and specific heat


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Calculating Heat: Formula:

Heat (J) = specific heat (J/kgC) x mass (kg)

x

change in temperature (C)

You can now calculate the heat transferred to

the water

Heat increasing (positive value)

Heat decreasing (negative value)


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Quick Quiz: Heat is the transferbetween 2 objects with different

temperatures. (T/F)

Convection currents result from temperature differences

in liquids and gases (T/F)

Radiation is the means by which the energy from the

sun is transferred to the Earth (T/F)

Water stays warm or cool longer than land does

because water has a lower specific heat than land does

(T/F)

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What is Heat Ch 10.2 8th