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from abc import ABC, abstractmethod
from sympy import Symbol, sympify
from sympy.physics.vector import Point
__all__ = ['BodyBase']
class BodyBase(ABC):
"""Abstract class for body type objects."""
def __init__(self, name, masscenter=None, mass=None):
# Note: If frame=None, no auto-generated frame is created, because a
# Particle does not need to have a frame by default.
if not isinstance(name, str):
raise TypeError('Supply a valid name.')
self._name = name
if mass is None:
mass = Symbol(f'{name}_mass')
if masscenter is None:
masscenter = Point(f'{name}_masscenter')
self.mass = mass
self.masscenter = masscenter
self.potential_energy = 0
self.points = []
def __str__(self):
return self.name
def __repr__(self):
return (f'{self.__class__.__name__}({repr(self.name)}, masscenter='
f'{repr(self.masscenter)}, mass={repr(self.mass)})')
@property
def name(self):
"""The name of the body."""
return self._name
@property
def masscenter(self):
"""The body's center of mass."""
return self._masscenter
@masscenter.setter
def masscenter(self, point):
if not isinstance(point, Point):
raise TypeError("The body's center of mass must be a Point object.")
self._masscenter = point
@property
def mass(self):
"""The body's mass."""
return self._mass
@mass.setter
def mass(self, mass):
self._mass = sympify(mass)
@property
def potential_energy(self):
"""The potential energy of the body.
Examples
========
>>> from sympy.physics.mechanics import Particle, Point
>>> from sympy import symbols
>>> m, g, h = symbols('m g h')
>>> O = Point('O')
>>> P = Particle('P', O, m)
>>> P.potential_energy = m * g * h
>>> P.potential_energy
g*h*m
"""
return self._potential_energy
@potential_energy.setter
def potential_energy(self, scalar):
self._potential_energy = sympify(scalar)
@abstractmethod
def kinetic_energy(self, frame):
pass
@abstractmethod
def linear_momentum(self, frame):
pass
@abstractmethod
def angular_momentum(self, point, frame):
pass
@abstractmethod
def parallel_axis(self, point, frame):
pass
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