[blocks and roller] Showing two blocks on the slopes of a triangle. #manim #geometry #physics

20240226_blocks.py

# https://www.reddit.com/r/manim/comments/1b0mkad/help_making_an_animation_for_a_physics_explainer/
class blocks(Scene):
    def construct(self):
        height = 5
        tri = Polygon(
            [-height*np.tan(30*DEGREES),-3,0],
            [height*np.tan(60*DEGREES),-3,0],
            [0,height-3,0]
        )
        tri.shift(-tri.get_center()[0]*RIGHT)
        self.add(tri)

        shift = ValueTracker(0)

        left_block = Rectangle(
            width=1,
            height=1,
        )
        left_block.shift(tri.get_vertices()[0]-left_block.get_critical_point(DL))
        left_block.rotate(60*DEGREES, about_point=tri.get_vertices()[0])

        def left_block_updater(mobj):
            mobj.shift(
                tri.get_vertices()[0]
                +shift.get_value()*np.array([np.cos(60*DEGREES),np.sin(60*DEGREES),0])
                -mobj.get_vertices()[2]
            )
        left_block.add_updater(left_block_updater, call_updater=True)

        right_block = Rectangle(
            width=2,
            height=1,
        )
        right_block.shift(tri.get_vertices()[2]-right_block.get_critical_point(DL))
        right_block.rotate(-30*DEGREES, about_point=tri.get_vertices()[2])
        def right_block_updater(mobj):
            mobj.shift(
                tri.get_vertices()[2]
                +shift.get_value()*np.array([np.cos(30*DEGREES),-np.sin(30*DEGREES),0])
                -mobj.get_vertices()[2]
            )
        right_block.add_updater(right_block_updater, call_updater=True)

        roler_dist = 0.35  # from apex
        roler_axis = tri.get_vertices()[2]+roler_dist*np.array([-np.sin(15*DEGREES),np.cos(15*DEGREES),0])
        roler_radius = 0.5-roler_dist/np.sqrt(2)
        roler = always_redraw(lambda:
            VGroup(
                Circle(radius=roler_radius).shift(roler_axis),
                *[Line(roler_axis, roler_axis+roler_radius*RIGHT).rotate(2*PI/5*i-shift.get_value()/(PI*roler_radius), about_point=roler_axis)  for i in range(5)]
            ).set_color(RED)
        )

        rope_left = always_redraw(lambda:
            Line(
                roler[0].point_at_angle(150*DEGREES),
                0.5*(left_block.get_vertices()[3]+left_block.get_vertices()[0]),
                color=YELLOW
            )
        )
        rope_right = always_redraw(lambda:
            Line(
                roler[0].point_at_angle(60*DEGREES),
                0.5*(right_block.get_vertices()[1]+right_block.get_vertices()[2]),
                color=YELLOW
            )
        )
        rope_on_roler = Arc(
            radius=roler_radius,
            start_angle=60*DEGREES,
            angle=90*DEGREES,
            color=YELLOW
        ).shift(roler_axis)

        self.add(left_block, right_block, roler, rope_left, rope_right, rope_on_roler)
        self.play(shift.animate.set_value(4), run_time=4, rate_func=rate_functions.linear)
        self.play(shift.animate.set_value(0), run_time=4, rate_func=rate_functions.there_and_back)
        self.wait()

readme.md

https://www.reddit.com/r/manim/comments/1b0mkad/help_making_an_animation_for_a_physics_explainer/