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| from sympy import symbols | |
| from sympy.physics.mechanics import Point, Particle, ReferenceFrame, inertia | |
| from sympy.physics.mechanics.body_base import BodyBase | |
| from sympy.testing.pytest import raises, warns_deprecated_sympy | |
| def test_particle_default(): | |
| # Test default | |
| p = Particle('P') | |
| assert p.name == 'P' | |
| assert p.mass == symbols('P_mass') | |
| assert p.masscenter.name == 'P_masscenter' | |
| assert p.potential_energy == 0 | |
| assert p.__str__() == 'P' | |
| assert p.__repr__() == ("Particle('P', masscenter=P_masscenter, " | |
| "mass=P_mass)") | |
| raises(AttributeError, lambda: p.frame) | |
| def test_particle(): | |
| # Test initializing with parameters | |
| 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 isinstance(p, BodyBase) | |
| 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) | |