# Force: Gravity

Model ElementForce_Gravity defines the acceleration due to gravity along the global X, Y, and Z directions.

## Format

```
<Force_Gravity
grav_x = "
```*real"*
grav_y = "*real"*
grav_z = "*real"* >
/>

## Attributes

`grav_x`- Defines the acceleration due to gravity in the global X direction. The default value is 0.0.
`grav_y`- Defines the acceleration due to gravity in the global Y direction. The default value is 0.0.
`grav_z`- Defines the acceleration due to gravity in the global X direction. The default value is 0.0.

## Example

The example below shows the gravity components in SI units.

```
<Force_Gravity
grav_x = "0."
grav_y = "0."
grav_z = "-9810."
/>
```

The following example shows gravity components modeled as a function of time.

```
<Force_Gravity
grav_x = "9810*STEP(TIME,0,0,2,1)"
grav_y = "0."
grav_z = "-9810*STEP(TIME,0,1,2,0)"
/>
```

## Comments

`grav_x`,`grav_y`,`grav_z`may be specified as real numbers or as function expressions. This allows you to model gravity as a function of time. If gravity is modeled as a function of displacements, forces or other states of the system, MotionSolve may have difficulty finding a converged solution.To represent state dependent gravity effects, use Force_Vector_TwoBody.

- The dimension of acceleration due gravity is: L
T
^{-2}.