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HEAT (PART 1)8TH GRADE
CHAPTER 21 SECTION 2
DO NOW…CONVERSION PRACTICE
•The temperature of the science lab is 70 F. What is this temperature in Celsius?
•The temperature outside is 25 C. What is this temperature in Fahrenheit?
THERMAL ENERGY (FROM YESTERDAY)
Potential Energy
•1) Molecules in a material exert attractive forces on each other
•Ex: Gravity exerts an attractive force on a ball.
•2) Molecules in a material have potential energy
•Ex: A ball above the ground has potential energy.
•3) As molecules move closer together or farther apart, potential energy changes
•Ex: As a ball moves closer to or farther from Earth’s surface, its potential energy changes.
OBJECTIVES
Students will…
•Explain the difference between thermal energy and heat
•Describe 3 ways thermal energy is transferred
HEAT AND THERMAL ENERGY
• Heat is the transfer of thermal energy from one object to another when objects are at different temperatures.
• The amount of thermal energy that is transferred when 2 objects are brought into contact depends on the difference in temperature between objects.
20 degree
s
100 degree
s
60 degree
s
60 degree
s
CONDUCTION, RADIATION AND CONVECTION
• Transfer of thermal energy by direct contact by collisions between particlesConducti
on
• Transfer of energy by electromagnetic waves
Radiation
• Transfer of thermal energy by the movement of particles in a gas or liquid
Convection
CLASSIFYING TYPES OF ENERGY TRANSFER
•Complete each sentence using radiation, convection or conduction
•1) The sun’s rays heat sand particles by ____________.
•2) Cool air pushes in to replace warm, air flow by natural _____.
•3) Body heat is transferred in to the air by _______.
•4) Heat from the sun warms iced tea by __________.
•5) A fan pushes air molecules by forced__________.
MINI LAB: COMPARING RATES OF MELTING
•Purpose: Observe the effect of ice water on melting ice.
•Lab procedures/directions
•Complete lab worksheet.
•Questions?
FOR NEXT TIME….
•Read pgs. 616-617
•Define convection, conductor, specific heat and thermal pollution on index cards.
•Test signed by Thursday.
HEAT (PART 2)8TH GRADE
CHAPTER 21 SECTION 2
MINI LAB
OBJECTIVES
Students will…
•Identify materials as insulators or conductors
•Complete mini-lab to observe convection
THERMAL CONDUCTORS VS. THERMAL INSULATORS
Thermal Conductors
- Conducts heat easily
-gold and copperMaterial contains
loosely held electrons
Thermal Insulators- Does not
conduct heat easily
-materials do not contain loosely held electrons
Depend on how strongly atoms hold electrons
HEAT ABSORPTION
•Specific Heat- is the amount of thermal energy needed to raise the temperature of 1kg of the substance by 1 degree C.
•More thermal energy is needed to change the temperature of a material with a high specific heat than one with a low specific heat.
•Ex: sand on a beach has lower specific heat than ocean water
THERMAL POLLUTION
•Thermal pollution- increase in the temperature of a body of water caused by adding warmer water.
•Effects: organisms need more oxygen and warmer water has less dissolved oxygen=organisms die due to low oxygen. Also organisms are more sensitive to chemical pollutants, parasites and disease.
•Reducing: Cooling warm water produced by factories, power plants and run off.
MINI LAB: OBSERVING CONVECTION
Purpose: Observe convection process
•Lab procedures/directions
•Safety precautions (esp. wearing goggles during experiment!)
•Complete lab worksheet
•Proper clean up
•Questions?
FOR NEXT TIME…
Khan Academy Videos
•Converting F to C
•Comparing F and C
•Each lab group needs to bring a pair of oven mitts or pot holders.
