Key Idea: All atoms and molecules are in constant motion.

Students are expected to know that:

  1. Atoms and molecules of all matter are always moving.
  2. This is true for atoms or molecules of solids, liquids, and gases.
  3. Even when objects that are made up of these atoms and molecules appear not to be moving, the atoms and molecules that make up those objects are nonetheless themselves in constant motion.
  4. The motion of atoms or molecules can include moving back and forth with respect to a fixed point, around a fixed point, and/or past each other from one fixed point to another.
  5. The motion (speed and direction) of an atom or molecule can change when it undergoes collision with another atom or molecule resulting in one speeding up and the other slowing down.
  6. Because atoms and molecules are continually colliding with each other, the atoms/molecules of the substance do not have the same speed.

Boundaries:

  1. Students are not expected to know the terms rotation, translation, and vibration.
  2. They are also not expected to know that atoms and molecules of different substances move at different speeds at the same temperature.
  3. Students are not expected to know the special case of absolute zero temperature where, according to kinetic theory, there should be no motion.