The intermolecular force is the sum of all the forces between two neighboring molecules. The forces result from the actions of the kinetic energy of atoms and the slight positive and negative electrical charges on different parts of a molecule that affect its neighbors and any solute that may be present.
The three main categories of intermolecular forces are London dispersion forces, dipole-dipole interaction, and ion-dipole interaction. Hydrogen bonding is considered a form of dipole-dipole interaction, and so contributes to the net intermolecular force.
In contrast, intramolecular force is the sum of the forces that act within a molecule between its atoms.
The intermolecular force is measured indirectly using measurements of various properties, including volume, temperature, pressure, and viscosity.