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- from sympy.core.symbol import symbols
- from sympy.physics.mechanics import Point, Particle, ReferenceFrame, inertia
- from sympy.testing.pytest import raises, warns_deprecated_sympy
- def test_particle():
- m, m2, v1, v2, v3, r, g, h = symbols('m m2 v1 v2 v3 r g h')
- P = Point('P')
- P2 = Point('P2')
- p = Particle('pa', P, m)
- assert p.__str__() == 'pa'
- assert p.mass == m
- assert p.point == P
- # Test the mass setter
- p.mass = m2
- assert p.mass == m2
- # Test the point setter
- p.point = P2
- assert p.point == P2
- # Test the linear momentum function
- N = ReferenceFrame('N')
- O = Point('O')
- P2.set_pos(O, r * N.y)
- P2.set_vel(N, v1 * N.x)
- raises(TypeError, lambda: Particle(P, P, m))
- raises(TypeError, lambda: Particle('pa', m, m))
- assert p.linear_momentum(N) == m2 * v1 * N.x
- assert p.angular_momentum(O, N) == -m2 * r *v1 * N.z
- P2.set_vel(N, v2 * N.y)
- assert p.linear_momentum(N) == m2 * v2 * N.y
- assert p.angular_momentum(O, N) == 0
- P2.set_vel(N, v3 * N.z)
- assert p.linear_momentum(N) == m2 * v3 * N.z
- assert p.angular_momentum(O, N) == m2 * r * v3 * N.x
- P2.set_vel(N, v1 * N.x + v2 * N.y + v3 * N.z)
- assert p.linear_momentum(N) == m2 * (v1 * N.x + v2 * N.y + v3 * N.z)
- assert p.angular_momentum(O, N) == m2 * r * (v3 * N.x - v1 * N.z)
- p.potential_energy = m * g * h
- assert p.potential_energy == m * g * h
- # TODO make the result not be system-dependent
- assert p.kinetic_energy(
- N) in [m2*(v1**2 + v2**2 + v3**2)/2,
- m2 * v1**2 / 2 + m2 * v2**2 / 2 + m2 * v3**2 / 2]
- def test_parallel_axis():
- N = ReferenceFrame('N')
- m, a, b = symbols('m, a, b')
- o = Point('o')
- p = o.locatenew('p', a * N.x + b * N.y)
- P = Particle('P', o, m)
- Ip = P.parallel_axis(p, N)
- Ip_expected = inertia(N, m * b**2, m * a**2, m * (a**2 + b**2),
- ixy=-m * a * b)
- assert Ip == Ip_expected
- def test_deprecated_set_potential_energy():
- m, g, h = symbols('m g h')
- P = Point('P')
- p = Particle('pa', P, m)
- with warns_deprecated_sympy():
- p.set_potential_energy(m*g*h)
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