thermal energy ch 6 ms. patterson physical science 2012
TRANSCRIPT
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