Caption: The animation shows a metal bar
being heated at one end by a Bunsen burner flame. A zoom
into the bar reveals the closely-packed atoms of the metal.
Heat is a manifestation of the movement of the atoms. Cold
atoms (blue) do not move much, but the atoms (red) above the
flame have more energy, and vibrate more. Their energetic
vibrations are passed through collisions to their colder neighbours, making those vibrate more in turn. The process
continues as more heat is added to the system, and the bar