IPC Chapter 6 - Thermal Energy

I.Temperature: thermometers = Kelvin, Celsius, Fahrenheit

  1. Matter in motion – all matter is made of tiny particles (atoms & molecules) that are in constant motion -> KE
  2. Temperature- measurement of average Kinetic energy (KE) of the molecules in a substance (K)
  1. Thermal energy
  2. = sum of Kinetic and potential energy of all molecules in an object
  3. Heat transfers warm -> cool
  4. Thermal energy ^ as Temp ^
  5. Thermal energy ^ as Mass ^

Example: Glass vs beaker of water. Have same temperature, but beaker has more thermal energy because it has more mass

  1. Heat
  2. Warm chair? Thermal energy transferred from person to chair.
  3. Form of Energy (J)
  4. Warm -> cold
  5. Specific Heat
  6. = the amount of heat needed to raise the temp of 1 kg of some matl by 1 degree C (J/(kgK)): water = 4184; iron = 450
  7. Can be used to identify an object
  8. Water as a coolant b/c can absorb heat w/out a large change in temp. (strong bonds); takes longer to cool down
  9. Calculate changes in thermal energy
  10. change in thermal energy = mass x change in temp x spec. heat
  11. change in temp = temp final – temp initial
  12. Q = m C T
  13. Ex: The temp of a 32 g silver spoon increases from 20 degrees C to 60 degrees C. If silver has a spec. heat of 235 J/kgK, what is the change in the thermal energy of the spoon?

M = 32g = .032 kg

C = 235 J/kgK

Ti = 20 C

Tf = 60 C

Q = ?

Q = m delta TC

= .032 kg x (60-20) x 235 J/kgK

= 301 J

  1. delta T = (+); Q = (+);when heat flows into object, temperature rises
  2. delta T = (-); Q = (-);When heat flows out of an object, temperature decreases
  3. Calories- unit commonly used to measure heat; measured by calorimeter (food labels)

6.2 Transferring thermal energy

  1. Transfer of Heat, Climate
  2. Conduction: Transfer of heat energy throughout a substance by DIRECT CONTACT. (soup spoon)
  3. Depends on collision between the molecules of a substance.
  4. Solids and metals are good conductors b/c particles close and electrons move easily (pots made of metal)
  5. Heat transfer: Differences in weather conditions are due to transfer of heat energy. Heat energy from sun reaches Earth by radiation- (Equator difference vs. pole) Convection currents form as air is heated by Earth’s surface---these create our wind and rain patterns.
  6. Convection, Radiation, and Thermal Expansion
  7. Convection- transfer of heat energy by movement of a fluid (liquid or gas), creating convection currents. Hot air is less dense and rises, cool air sinks = current.

Example: oven

  1. Radiation- transfer of energy by infrared waves such as fire or the sun. When infrared waves strike your skin, the molecules vibrate faster and become warmer.

*Doesn’t require a medium-can travel through the vacuum of space.

  1. Radiation in Solids, Liquids, and Gases

In all phases, radiant energy can travel through the space between molecules. Because molecules are farther apart in gases than in solids or liquids, radiation passes more easily through gases

  1. Controlling Heat Flow

Almost all living things have special features that help them control heat flow.

Example: fur and blubber (penguins); Lizard’s scaly skin (reflects)

-We use things such as coats to keep out cold or oven mitts to keep out heat.

  1. Insulators- Material that doesn’t allow heat to flow through it easily. Good conductors are poor insulators. Gases usually better than solids or liquids.

Example: Down, wood, plastic, fiberglass

  1. Thermal expansion- an increase in the volume of a substance
  2. Solids- Expansion joints between segments of the road prevent buckling of the concrete and metal as they expand.
  3. Liquids- Reason we don’t put unopened coke cans in the freezer and why water overflows when heated (boiling)
  4. Gases- Over inflated tires burst after long trips due to gas molecules heating up.
  1. Temperature scales

A. Celsius: C = K – 273

  1. Kelvin: K = C + 273

1. Absolute zero- molecules in a substance are so cold they quit moving and have no KE.