Thermal Energy Ch 6 Ms. Patterson Physical Science 2012

Thermal EnergyCh 6

Ms. Patterson

Physical Science 2012

Schedule for the rest of the year

Objectives

• 6-1 Explain the difference between heat and temperature• 6-2 Determine the thermal energy for any amount of

substance• 6-3 Determine if an item is an insulator or a conductor• 6-4 Determine the type of heat transfer – conduction,

convection or radiation• 6-5 Explain the difference between types of heat transfer

– conduction, convection or radiation

Section 1 - Heat

Objectives: 6-1 Explain the difference between heat

and temperature

Heat• DEF: Energy that flows

from high temperature to low temperature

• Which way is the heat flowing?

Temperature

• DEF: a measure of the average kinetic energy of the molecules of a substance

Temperature Scales

• Classroom is celsius (°C)• Scientific is kelvin (K)• Everyday is fahrenheit (°F)

ConversionsPut these on your formula sheet

°C + 273 = K

°F = °C+32

°C = (°F-32)

9

5

5

9

Now let’s practice

• 58 °C = ________________ K

• 156 °F= ________________ °C

• 91 °C = ________________ °F

Specific Heat• DEF: The amount of heat energy (J)

needed to raise the temperature of 1kg of some material by 1C

• Aka: the ability of a material to absorb or release heat.

Requires Tools Needed

•Mass of substance Balance

•Change in temperature

Thermometer

•Specific heat of substance

Resource Chart

Substance Specific Heat in J/g°C

Aluminum CopperBrassSilverGoldLead

MercuryWaterIron

Ice (-10 C)Glass

0.90.3860.38

0.2350.1260.1280.14

4.1840.4502.05 0.84

Comparison - Which has more heat?

• 5 kg of water at 100C

• 1 kg of water at 100C

1 kg of water at 70C

1 kg of iron at 70C

Exa

mpl

e 1

Exa

mpl

e 2

Q = m * c * (Tf-Ti)

Measurement Variables Units

change in thermal energy Q J

mass m g or kg

specific heat CJ/g°C orJ/kg°C

change in temperature(Tf-Ti)

∆T °C

• A 30 g silver spoon cools from 60°C to 20°C. How much thermal energy did it lose? C = .235 j/g*°C

Q = m * c * (Tf –Ti)Q = 30 g * .235 J/gC * 40 C Q = 282 J

How much mass is present if -368J of thermal energy are given off when water in a pond cools from 12°C to 10°C? C = 4.184 j/g°C

• What is the specific heat of glass if a window pane with a mass of 230 g warms from 12°C to 20°C and the change in thermal energy is 1,546 J?

Section 2 – Transferring Thermal Energy

Objectives• 6-3 Determine if an item is an insulator or a

conductor• 6-4 Determine the type of heat transfer –

conduction, convection or radiation• 6-5 Explain the difference between types of heat

transfer – conduction, convection or radiation

Conduction

• DEF: Heat transfer when the molecules in 2 objects touch–Happens in

•Solids, liquids, gases

• Conductors •DEF: material that passes heat well•Examples: silver, copper, and aluminum

• Insulators•DEF: material that does not pass heat well

•Examples: Wood, plastic, air, paper, cloth

Radiation• DEF: Heat transfer through electromagnetic waves•No matter needed for transfer!

• Examples•Infrared light•Heat from a fire or hot stove•Energy from the sun!

(

Convection• DEF: heat transfer through

movement of fluids

• When a fluid is heated, it expands, becomes less dense, and rises. Cooler fluid then settles to the bottom.

• Examples–Convection currents - soaring birds (aka. kettles), convection ovens, lava lamps

Convection Currents

Convection Currents

Heat Transfer