There are 2 types of forcefield, linear and radial, these can provide effect like gravity, wind and water.
linearforcefields can simulate a number of very different effects depending on their settings.
If a linearforcefield has no size attribute (or it is left blank) then it is an ambient field, and it affects the entire level. Almost all of the original levels have an ambient field providing the gravity.
linearforcefields can also be localized by giving them a size and a center. In this case only objects inside the field are affected by it. This is used most commonly to simulate wind or to support the Goo Balls when they are sitting on a cloud.
When the water attribute is set to true, the game displays the water effect within the field in the given color. The top edge of the field is given surface ripples and makes little splashes when objects enter or leave at speed. However beyond these visual differences the field's physics operates in the same way as any other Local field.
These fields are also used to provide a gravity effect, but on a larger scale. Used in Graphics Processing Unit and Main World View to give the orbiting effect. These fields cannot be ambient, so they must always have a center and a radius specified. The type,antigrav and dampeningfactor attributes work the same as linearforcefields see above
This attribute can be applied to linear fields. When set to true the field only affects dynamic geometry objects and not Goo Balls. This can be useful in the construction of mechanisms - [link to...]
Note: geomonly tag was present on all radialforcefields in the original levels, but doesn't have any effect when set to true, so was removed from WooGLE in v0.74