Balloons can be used to model molecules attached to a surface. In this case
the balloons are filled with helium and have a steel ball as a weight in one
end. A breeze is used to model thermal energy.
Balloons as models.
Deposition of molecules on a surface.
Molecules on a surface are in constant motion.
An increase in ambient energy on the left side of the surface causes a drift in surface coverage.
A step edge is higher in energy.
When ambient energy is increased the surface-molecular attraction may
no longer hold the molecules.