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Key Idea: Energy is transferred through a material by conduction by the random collisions of atoms and molecules that make up the material.

Students should know that:

  1. The atoms and molecules that make up an object are constantly in motion, and when they collide they transfer energy from one to another. 
  2. When rapidly moving atoms or molecules collide with slower moving atoms, there is a net energy transfer from the rapidly moving atoms to the slower moving atoms. The slower moving atoms increase in speed while the rapidly moving atoms decrease in speed.
  3. Energy is transferred from a warmer part of an object to a cooler part of the object or from a warmer object to a cooler object when the objects are in contact, through the random collisions of atoms or molecules.
  4. When the faster moving atoms and molecules of a warmer object (or part of an object) collide with the slower moving atoms and molecules of a cooler object (or part of an object), the average speed of the faster moving atoms and molecules decreases, which means that the warmer object (or part of an object) gets cooler and, therefore, has less thermal energy than before.  The average speed of the slower moving atoms and molecules of the cooler object increases, which means that the cooler object (or part of an object) gets warmer and, therefore, has more thermal energy than before.
  5. Different substances will transfer energy by conduction at different rates depending on the types of atoms/molecules that make them up.
  6. The transfer of energy by conduction typically occurs faster in solids and liquids than in gases because the atoms or molecules that make up a solid or liquid are more closely packed compared to the atoms or molecules that make up gases, and therefore the atoms and molecules that make up a solid or liquid are in closer proximity to other molecules with which they can interact.

 

Boundaries:

  1. Items do not ask students to calculate how much energy is transferred by conduction in a particular situation.
  2. Contexts of assessment items are limited to those that do not involve changes of state.
  3. While the mass of the atoms or molecules of a substance and interatomic bonding play a role in determining how much kinetic energy the atoms or molecules have and, therefore, how much energy can be transferred by conduction, items use contexts in which the atoms or molecules of the warmer object are moving faster than the atoms or molecules of the cooler object so that mass or bonding do not have to be considered.