From LightWiki

GravityFX is a force which will accelerate HardFX, ClothFX, SoftFX and ParticleFX items, affecting them by their weight.

• Group - Controls which Dynamics Group this effect belongs to.
• Size Effect - Chooses how the size of the Gravity item affects it. Setting it to Gravity means the size will be multiplied by the strength of the gravity, setting it to Region, means the size will change the area that the gravity will affect.
• Gravity Mode - This determines the direction the gravity is applied. Direction will use the Gravity(m/s^2) vector setting below to accelate the dynamic object in that direction. Point will accelerate the item away or (if Power is negative ) towards a point. This is good for planets etc. 2-pole is like the Earth's magnetic field, pushing away from one point and towards another.
• Falloff Mode - This controls how far the force extends. It can be Linear, starting at 100% at the centre and falling off to 0% at the Radius, Inverse distance, starting at 100% then falling off quickly but never quite reaching 0%, like a planet's gravity, or OFF.
• Radius - This is the distance used by Falloff Mode.
• Power - The strength of the gravity.
• Gravity (m/s^2) - This also affects the strength, but determines the direction of the gravity, if the Gravity is using it. You can also rotate the gravity item to change the gravity's pull.

If the gravity is directional, you can get localised Earth style gravity either setting Power to 981% and Gravity (m/s^2) to <0,-1,0> or Power to 100% and Gravity to <0,-9.81,0> or some other way of multiplying Power X Gravity to equal <0,-9.81,0>.