To create a gravity control object: Choose Get 
Force Gravity from the Simulate toolbar, Get Primitive Control Object Gravity from the other toolbars, or Create Force Gravity from the Hair toolbar.
To redisplay this property editor: Select the gravity object and press Enter.
The Gravity force simulates a gravitational pull on simulated objects, including in a negative direction.
Gravity is the most common type of "force" that you will use, for obvious reasons. Gravity is actually a constant that is the same for all objects regardless of their mass: every object falls at the same rate (remember Galileo and Newton?). However, everything changes at the moment there is air resistance/friction or when the object collides with another because that's where its mass, energy, and momentum play a major role.
For more information on forces in general, see Forces [ Simulation].
To use this force in an ICE tree, see Creating and Applying ICE Forces to ICE Simulations [ICE Fundamentals].
Length of the arrow is determined by the Amplitude value.
