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.. _types-of-forces:

Types of forces
===============

Panda3D provides two types of forces that you can apply to an object.

LinearVectorForce
-----------------

A ``LinearVectorForce`` treats the object as
a point mass. It applies an acceleration in Newtons to the center of mass of
the object it was added to. The direction of this force is relative to the
orientation of the ``ForceNode`` that
the ``LinearVectorForce`` was applied to.

*Note: Since ``LinearVectorForce`` treats the
object as a point mass, it is not possible to apply a rotation of any kind to
your object. For rotational forces, see
``AngularVectorForce`` below.*

**Example:** 

.. code-block:: python

     
    lvf=LinearVectorForce(1,0,0)  # Push 1 newton in the positive-x direction 
    forceNode.addForce(lvf)  # Determine coordinate space of this force node
    actorNode.getPhysical(0).addLinearForce(lvf) # Add the force to the object



AngularVectorForce
------------------

The ``AngularVectorForce`` applies a torque to
the object it is attached to. The acceleration is in Newtons, and
``AngularVectorForce`` may be treated in much
the same way as ``LinearVectorForce``. There
are, however, some minor differences that that should be taken into account.

``AngularVectorForce`` does not have a
``.setDependantMass()``. The reason for this
is simple: mass **must** be used in the torque calculations. As such, you will
want to make sure your forces are sufficiently small or your masses are
sufficiently large to keep your rotational velocity sane.

**Example:** 

.. code-block:: python

     
    avf=AngularVectorForce(1,0,0) # Spin around the positive-x axis 
    forceNode.addForce(avf) # Determine which positive-x axis we use for calculation
    actorNode.getPhysical(0).addAngularForce(avf) # Add the force to the object



One additional caveat with
``AngularVectorForce``: Angular forces will
not be processed on your object until an
``AngularIntegrator`` is added to the
``PhysicsManager``.

**Example:** 

.. code-block:: python

     
    from panda3d.physics import AngularEulerIntegrator
    
    angleInt = AngularEulerIntegrator() # Instantiate an AngleIntegrator()
    base.physicsMgr.attachAngularIntegrator(angleInt) # Attatch the AngleIntegrator to the PhysicsManager



*Editor's Note: Each type of force should be given it's own page with much
more in depth examples, and perhaps a small sample program.*