London-van der Waals Force

Table 1. van der Waals force for a m particles.  For comparison  and  a separation of is assumed.

Particle	Surface	(In air)		(In water)
Polystyrene	Polystynene	1.2-1.8	70-100	0.2	12
Si	Si	13.6-14.4	800-850	7	410
Cu	Cu	17	1000	9.8	580
Ag	Ag	18	1060	15.5	910

Table 2: Variation of Forces (N) versus particle diameter, d (μm), or a flow velocity of
	Van der Waals	Surface Tension	Added Mass	Drag/Lift	Basset
Diameter
Air
d (μm)
0.2
2
20
Water
d (μm)
0.2		___
2		___
20		___

Values of van der Waals, surface tension, added mass, drag and Basset forces acting on a sphere of different sizes moving with a velocity of 10 m/s are shown in Table 2. For a particle in air, it is seen that the surface tension force is order of magnitudes larger than the other forces, which is followed by the van der Waals force. Among the hydrodynamic forces, drag is the dominating force and the virtual mass and the Basset forces are negligibly small. In water, the surface tension force is absent and the drag force acting on large particles beomes comparable with the van der Waals adhesion force.