'Linear momentum of the rigid body.
The linear momentum L, of a rigid body B, with respect to frame N is
given by
L = M * v*
where M is the mass of the rigid body and v* is the velocity of
the mass center of B in the frame, N.
Parameters
frame : ReferenceFrame
The frame in which linear momentum is desired.
Examples
>>> from sympy.physics.mechanics import Point, ReferenceFrame, outer
>>> from sympy.physics.mechanics import RigidBody, dynamicsymbols
>>> M, v = dynamicsymbols(\'M v\')
>>> N = ReferenceFrame(\'N\')
>>> P = Point(\'P\')
>>> P.set_vel(N, v * N.x)
>>> I = outer (N.x, N.x)
>>> Inertia_tuple = (I, P)
>>> B = RigidBody(\'B\', P, N, M, Inertia_tuple)
>>> B.linear_momentum(N)
M*v*N.x'

def linear_momentum(self, frame):

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