Field of force due to point mass

Forces and Torques

This block represents the gravitational field of a point mass. This field applies a gravitational force at the center of mass of each rigid body. The force magnitude decays with the square distance from the field origin, coincident with the base port frame origin. The force on a rigid body follows from Newton’s universal gravitation law:

$${F}_{g}=-\text{\hspace{0.17em}}G\frac{Mm}{{R}_{BF}{}^{2}},$$

*F*_{g}is the force that the gravitational field exerts on a given rigid body.*G*is the universal gravitational constant, 6.67384 × 10^{-11}m^{3}kg^{-1}s^{-2}.*M*is the total mass generating the gravitational field.*m*is the total mass of the rigid body the gravitational force acts upon.*R*_{BF}is the distance between the source mass position and the rigid body center of mass.

The figure shows these variables. The plot shows the inverse square dependence between the gravitational force and distance.

The source mass can be positive or negative. Combine multiple instances of this block to model the gravitational effects that positive and negative mass disturbances impose on a stronger gravitational field, such as a reduction in the gravitational pull of a planet due to a concentration of low-density material along a portion of its surface.

This block excludes the gravitational forces that other rigid bodies exert on the field source mass. To include these forces, you can connect Gravitational Field blocks to other rigid bodies in the model. Alternatively, you can use the Inverse Square Law Force block to model the gravitational forces between a single pair of rigid bodies.

The gravitational field is time invariant. To specify a time-varying, spatially uniform field, use the Mechanism Configuration block.

This block supports code generation for real-time simulation
tasks. Certain blocks and block settings may be more suitable for
simulation on a real-time device. For suggestions on how to improve
real-time simulation performance, use the Simulink^{®} Performance
Advisor (Simulink). Suggestions include ways to reduce model complexity
where helpful and to decrease numerical stiffness.

Select **Analysis** > **Performance Tools** > **Performance
Advisor** in the Simulink menu bar to
open the Performance Advisor. Set the **Activity** parameter
to `Execute real-time application`

to view
suggestions specific to real-time simulation performance. Expand the **Real-Time** node
in the tree view pane to select performance checks specific to Simscape™ products.

**Mass**Total mass generating the gravitational field. The resulting gravitational forces are directly proportional to this mass. This mass adds no inertia to the model. The default value for the mass parameter is

`1.0`

kg.

Frame port B represents a frame with origin at the point mass responsible for the gravitational field.

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