Final answer:
Dispersion forces, or London dispersion forces, are the weakest type of intermolecular force, significant in all atoms and molecules due to electron motion.
Step-by-step explanation:
The weakest type of force between particles of a substance is termed dispersion force, also known as the London dispersion force. These are a type of van der Waals force and are the weakest of all intermolecular forces. They occur between all atoms and molecules due to the random motion of electrons, resulting in temporary dipole moments that cause a weak electrostatic attraction between the particles.