Body (Docstrings)

Body

class sympy.physics.mechanics.body.Body(name, masscenter=None, mass=None, frame=None, central_inertia=None)

Body is a common representation of RigidBody or a Particle.

A Body represents either a rigid body or particle in classical mechanics. Bodies have a body-fixed reference frame, a mass, a mass center and possibly a body-fixed inertia.

Parameters:

name: String

Defines the name of the body. It is used as the base for defining body specific properties.

masscenter : Point, optional

A point that represents the center of mass of the body or particle. If no point is given, a point is generated.

frame : ReferenceFrame (optional)

The ReferenceFrame that represents the reference frame of the body. If no frame is given, a frame is generated.

mass : Sympifyable, optional

A Sympifyable object which represents the mass of the body. if no mass is passed, one is generated.

body_inertia : Dyadic

Central inertia dyadic of the body. If none is passed while creating RigidBody, a default inertia is generated.

Examples

Default behaviour. It creates a RigidBody after defining mass, mass center, frame and inertia.

>>> from sympy.physics.mechanics import Body
>>> body = Body('name_of_body')

Passing attributes of Rigidbody. All the arguments needed to create a RigidBody can be passed while creating a Body too.

>>> from sympy import Symbol
>>> from sympy.physics.mechanics import ReferenceFrame, Point, inertia
>>> from sympy.physics.mechanics import Body
>>> mass = Symbol('mass')
>>> masscenter = Point('masscenter')
>>> frame = ReferenceFrame('frame')
>>> ixx = Symbol('ixx')
>>> body_inertia = inertia(frame, ixx, 0, 0)
>>> body = Body('name_of_body',masscenter,mass,frame,body_inertia)

Creating a Particle. If masscenter and mass are passed, and inertia is not then a Particle is created.

>>> from sympy import Symbol
>>> from sympy.physics.vector import Point
>>> from sympy.physics.mechanics import Body
>>> mass = Symbol('mass')
>>> masscenter = Point('masscenter')
>>> body = Body('name_of_body',masscenter,mass)

Similarly, A frame can also be passed while creating a Particle.

apply_force(vec, point=None)

Adds the force to the point (center of mass by default) on the body.

Parameters:

vec: Vector

Defines the force vector. Can be any vector w.r.t any frame or combinations of frame.

point: Point, optional

Defines the point on which the force must be applied. Default is Body’s center of mass.

Example

To apply a unit force in x direction of body’s frame to body’s center of mass.

>>> from sympy import Symbol
>>> from sympy.physics.mechanics import Body
>>> body = Body('body')
>>> g = Symbol('g')
>>> body.apply_force(body.mass * g * body.frame.x)

To apply force to any other point than center of mass, pass that point as well.

>>> from sympy import Symbol
>>> from sympy.physics.mechanics import Body
>>> parent = Body('parent')
>>> child = Body('child')
>>> g = Symbol('g')
>>> frame = parent.frame
>>> l = Symbol('l')
>>> point = child.masscenter.locatenew('force_point', l * body.frame.y)
>>> gravity = child.mass * g
>>> body.apply_force(gravity * body.frame.x, point)

apply_torque(vec)

Adds torque to the body.

Parameters:

vec: Vector

Defines the torque vector. Can be any vector w.r.t any frame or

combinations of frame.