Source code for sympy.physics.mechanics.particle

from __future__ import print_function, division

__all__ = ['Particle']

from sympy import sympify
from sympy.physics.mechanics.point import Point


[docs]class Particle(object): """A particle. Particles have a non-zero mass and lack spatial extension; they take up no space. Values need to be supplied on initialization, but can be changed later. Parameters ========== name : str Name of particle point : Point A physics/mechanics Point which represents the position, velocity, and acceleration of this Particle mass : sympifyable A SymPy expression representing the Particle's mass Examples ======== >>> from sympy.physics.mechanics import Particle, Point >>> from sympy import Symbol >>> po = Point('po') >>> m = Symbol('m') >>> pa = Particle('pa', po, m) >>> # Or you could change these later >>> pa.mass = m >>> pa.point = po """ def __init__(self, name, point, mass): if not isinstance(name, str): raise TypeError('Supply a valid name.') self._name = name self.set_mass(mass) self.set_point(point) self._pe = sympify(0) def __str__(self): return self._name __repr__ = __str__
[docs] def get_mass(self): """Mass of the particle.""" return self._mass
def set_mass(self, mass): self._mass = sympify(mass) mass = property(get_mass, set_mass)
[docs] def get_point(self): """Point of the particle.""" return self._point
def set_point(self, p): if not isinstance(p, Point): raise TypeError("Particle point attribute must be a Point object.") self._point = p point = property(get_point, set_point)
[docs] def linear_momentum(self, frame): """Linear momentum of the particle. The linear momentum L, of a particle P, with respect to frame N is given by L = m * v where m is the mass of the particle, and v is the velocity of the particle in the frame N. Parameters ========== frame : ReferenceFrame The frame in which linear momentum is desired. Examples ======== >>> from sympy.physics.mechanics import Particle, Point, ReferenceFrame >>> from sympy.physics.mechanics import dynamicsymbols >>> m, v = dynamicsymbols('m v') >>> N = ReferenceFrame('N') >>> P = Point('P') >>> A = Particle('A', P, m) >>> P.set_vel(N, v * N.x) >>> A.linear_momentum(N) m*v*N.x """ return self.mass * self.point.vel(frame)
[docs] def angular_momentum(self, point, frame): """Angular momentum of the particle about the point. The angular momentum H, about some point O of a particle, P, is given by: H = r x m * v where r is the position vector from point O to the particle P, m is the mass of the particle, and v is the velocity of the particle in the inertial frame, N. Parameters ========== point : Point The point about which angular momentum of the particle is desired. frame : ReferenceFrame The frame in which angular momentum is desired. Examples ======== >>> from sympy.physics.mechanics import Particle, Point, ReferenceFrame >>> from sympy.physics.mechanics import dynamicsymbols >>> m, v, r = dynamicsymbols('m v r') >>> N = ReferenceFrame('N') >>> O = Point('O') >>> A = O.locatenew('A', r * N.x) >>> P = Particle('P', A, m) >>> P.point.set_vel(N, v * N.y) >>> P.angular_momentum(O, N) m*r*v*N.z """ return self.point.pos_from(point) ^ (self.mass * self.point.vel(frame))
[docs] def kinetic_energy(self, frame): """Kinetic energy of the particle The kinetic energy, T, of a particle, P, is given by 'T = 1/2 m v^2' where m is the mass of particle P, and v is the velocity of the particle in the supplied ReferenceFrame. Parameters ========== frame : ReferenceFrame The Particle's velocity is typically defined with respect to an inertial frame but any relevant frame in which the velocity is known can be supplied. Examples ======== >>> from sympy.physics.mechanics import Particle, Point, ReferenceFrame >>> from sympy import symbols >>> m, v, r = symbols('m v r') >>> N = ReferenceFrame('N') >>> O = Point('O') >>> P = Particle('P', O, m) >>> P.point.set_vel(N, v * N.y) >>> P.kinetic_energy(N) m*v**2/2 """ return (self.mass / sympify(2) * self.point.vel(frame) & self.point.vel(frame))
[docs] def set_potential_energy(self, scalar): """Used to set the potential energy of the Particle. Parameters ========== scalar : Sympifyable The potential energy (a scalar) of the Particle. 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.set_potential_energy(m * g * h) """ self._pe = sympify(scalar)
@property
[docs] def potential_energy(self): """The potential energy of the Particle. 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.set_potential_energy(m * g * h) >>> P.potential_energy g*h*m """ return self._pe