$\newcommand{\deriv}[2][]{\dfrac{\partial #1}{\partial #2}} \newcommand{\tderiv}[2][]{\tfrac{\partial #1}{\partial #2}} \newcommand{\fderiv}[2][]{\dfrac{d #1}{d #2}} \newcommand{\derivII}[3][]{\dfrac{\partial^2 #1}{\partial #2 \partial #3}} \newcommand{\tderivII}[3][]{\tfrac{\partial^2 #1}{\partial #2 \partial #3}} \newcommand{\derivIII}[4][]{\dfrac{\partial^3 #1}{\partial #2 \partial #3 \partial #4}} \newcommand{\tderivIII}[4][]{\tfrac{\partial^3 #1}{\partial #2 \partial #3 \partial #4}} \newcommand{\derivIV}[5][]{\dfrac{\partial^4 #1}{\partial #2 \partial #3 \partial #4 \partial #5}} \newcommand{\half}{\tfrac{1}{2}} % Macro for 1/2 \newcommand{\ud}{\mathrm{d}} \newcommand{\op}{\circ} \newcommand{\dq}{\dot{q}} \newcommand{\ddq}{\ddot{q}} \newcommand{\dt}{\Delta t}$

Gravity – Basic Gravity

class trep.potentials.Gravity(system[, gravity=(0.0, 0.0, -9.8), name=None])

(Inherits from Potential)

Parameters:

• system (System) – An instance of System to add the gravity to.
• gravity (Sequence of three Float) – The gravity vector
• name – A string that uniquely identifies the gravity.

Gravity implements a basic constant acceleration gravity (\(F = m\vec{g}\)).

Implemented Calculations

Calculation	Implemented
V	Y
V_dq	Y
V_dqdq	Y
V_dqdqdq	Y

Examples

Adding gravity to a system is as easy as declaring an instance of Gravity:

>>> system = build_custom_system()
>>> trep.potentials.Gravity(system)
<Gravity 0.000000 0.000000 -9.800000>

The System saves a reference to the new Gravity, so we do not have to save a refence to prevent it from being garbage collected.

The default gravity points in the negative Z direction. We can specify a new gravity vector when we add the gravity. For example, we can make gravity point in the positive Y direction:

>>> system = build_custom_system()
>>> trep.potentials.Gravity(system, (0, 9.8, 0))
<Gravity 0.000000 9.800000 0.000000>

Gravity Objects

Gravity.gravity

The gravity vector for this instance of gravity.

Visualization

Gravity.opengl_draw()

Gravity does not draw a visual representation.