The Gravity space warp simulates the effect of natural gravity on particles generated by a particle system. Gravity is directional it adds pull to particles that are moving in its direction and repels particles moving in the opposite direction. Gravity has been updated to work with Dynamics in the Utillites topic.
Gravity effect on snow
These parameters control gravity space warps.
Strength: Increasing Strength increases the effect of gravity. Strength less than 0.0 creates negative gravity it repels particles moving in the same direction and attracts particles moving in the opposite direction. When Strength is 0.0, the gravity warp has no effect.
Decay: When Decay is 0.0, the gravity warp has the same strength throughout world space. Increasing the Decay value causes gravity strength to diminish as distance increases from the position of the gravity warp object. Default=0.0.
Planar: Gravity effect is perpendicular to the plane of the gravity warp object, throughout the scene.
Spherical: Gravity effect is spherical, centered on the gravity warp object. This is good for creating water fountain effects.
Icon Size: Size of the gravity warp object icon, in active units. You set the initial Icon Size value when you drag to create the gravity object. This value does not change the gravity effect.
The gravity icon appears. For planar gravity (the default), the icon is a wireframe square with a direction arrow coming out of one side. For spherical gravity, the icon is a wireframe sphere.
The initial direction of planar gravity is along the negative Z axis of the construction grid that is active in the viewport where you drag. You can rotate the gravity object to change the direction.