2. Thermal Energy
Thermal Energy: the sum of kinetic and potential energy of the particles in an object.
Thermal energy increases as mass increases.
Thermal energy increases as temperature increases.
Temperature: a measure of the average kinetic energy of particles in an object.
The higher the temperature, the faster the particles are moving.

3. How do you know if someone has been sitting in your chair?
Thermal Energy
How do you know if someone has been sitting in your chair?
Thermal energy always flows from higher temperature objects to lower temperature objects.
Heat: (Q) the transfer of energy from one object to another.
Measured in Joules.
I like to ask first question to get them thinking about how heat transfers from higher temp objects to lower temp.

4. Transfer of Thermal Energy
No such thing as “cold”
When you feel cold, you are simply feeling the absence of heat.
Example: Explain what happens when you hold a cold drink and your hand starts to feel “cold”.
When heat flows into an object, the change in heat is +
When heat flows out of an object, the change in heat is -
Answer: Heat leaves the higher temperature object (your hand) and transfers to the lower temperature object (the cup). This is why the cup starts to ”sweat” and condensation forms. This is also why your hand feels “cold” due to the absence of heat from the heat leaving your hand and going to the cup.

5. Transfer of Thermal Energy
Can be transferred 3 ways.
Conduction: transfer of energy through matter by direct contact of particles.
Solids are best conductors of heat.
Particles are already so close together so contact is easy.

6. Transfer of Thermal Energy
Can be transferred 3 ways.
Convection: transfer of energy by the movement of heated particles.
Occurs in liquids and gases.
Currents move heat from warmer to cooler parts of the substance.

7. Transfer of Thermal Energy
Can be transferred 3 ways.
Radiation: transfer of energy through electromagnetic waves.
Occurs fastest in gases.
Can be absorbed or reflected.
Can travel through space and between molecules.

8. Some materials transfer heat well, and others do not.
Conductors: materials that allow heat to flow easily
Ex. Metals and skin
Insulators: materials that do not allow heat to flow easily
Ex. Air, wood, styrofoam, plastic, fiberglass

9. Specific Heat
Specific Heat: the amount of heat needed to raise the temperature of 1 kg of a material by 1 °C or K.
Specific to different types of materials.
Measured by a calorimeter.
Q = mcΔT
Q = change in thermal energy (or heat)
Measured in J
m = mass
Measured in kg
c = specific heat
Measured in J/kg °C
ΔT = change in temperature (Tf – Ti)
Measured in °C

10. Example #1
A wooden block has a mass of 20 kg and a specific heat of 1,700 J/(kg oC). Find the change in thermal energy of the block as it warms from 15 oC to 25 oC.
Q = (20)(1700)(25-15)
Q = (20)(1700)(10)
Q = 340,000 J
m = 20.0 kg
C = 1700 J/(kg oC)
Ti = 15 oC
Tf = 25 oC
Q = ?
Q = mcΔT
Q = mc(Tf – Ti)

11. Practice Time
The air in a living room has a mass of 60 kg and a specific heat of 1,020 J/kg oC. What is the change in thermal energy of the air when it warms from 20 oC to 25 oC?
The thermal energy of water in a mug increases by 12,552 J when the water is heated from 20 oC to 40 oC. If the specific heat of water is 4,184 J/kg oC, what is the mass of the water?
Answer: Q = 306,000 J
I have students work these out in their notes and I walk around and help them as they work. Then we go over the answers all together. I especially encourage CP students that if they don’t know what to do, they at least need to set up the problem (labeling values that they know and writing the appropriate equation.) They should NEVER leave a problem blank!
CP can definitely do rearranging problems with this equation, like in #2. It will just be more of a challenge for them.
Again, #2 would definitely be challenge or bonus question for CP, but I still like to talk through these with them because it is good for them to be challenged! These would be required for honors for sure.
Answer: m = 0.15 kg