Use the Gravity Force node to exert a gravitational force on particles. By specifying the density of the surrounding fluid, the effect of buoyancy on the particle motion can also be included. The gravity vector can point in any direction with any magnitude, although the default is for particles to move downward using the acceleration due to gravity at Earth’s surface. For submicron particles, the drag and other external forces can dominate, so gravity can often have little effect on the particle trajectories.

Enter coordinates based on space dimension for the Gravity vector g (SI unit: m/s2). The default magnitude for the gravity vector is g_const, which is a built-in physical constant equal to g = 9.80665 m/s2 corresponding to the standard acceleration due to gravity on Earth. The default direction is the negative y direction in a 2D geometry or the negative z direction for a 2D axisymmetric or 3D geometry.

The default Density ρ (SI unit: kg/m3) is taken From material, from a physics interface that defines or computes the density, or select User defined to enter another value or expression.

Use the Particles to affect list to apply the force to specific particles. The available settings are the same as for the Force node.