'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'

def linear_momentum(self, frame):

    return (self.mass * self.point.vel(frame))
