From 5fa3109fdc1b750e1aa2fb8a0ed51bfb1195bdb4 Mon Sep 17 00:00:00 2001
From: Heejin Park <rhaos68@naver.com>
Date: Wed, 30 Sep 2020 20:29:17 +0900
Subject: [PATCH] explain_radian

---
 explain_radian.py | 91 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 explain_radian.py

diff --git a/explain_radian.py b/explain_radian.py
new file mode 100644
index 0000000..3e12579
--- /dev/null
+++ b/explain_radian.py
@@ -0,0 +1,91 @@
+from manimlib.imports import *
+
+class ExplainRadian(Scene):
+    def construct(self):
+        R = 2
+        A = np.array([R,0,0])
+        #A = circle.point_from_proportion(0)
+
+        #1. draw circle
+        circle = Circle(radius=R)
+        o_dot = Dot(color=BLUE).move_to(circle.get_center())
+        o_text = TextMobject("O").next_to(circle.get_center(),DOWN)
+        self.add(circle, o_dot, o_text)
+
+        #2. draw r
+        r_line = Line(circle.get_center(), circle.point_from_proportion(0), color=BLUE)
+        a_dot = Dot(color=BLUE).move_to(A)
+        a_text = TextMobject("A").next_to(A, RIGHT)
+        r_text = TextMobject("r", color=BLUE).next_to(r_line, DOWN)
+        self.play(
+            LaggedStart(
+                ShowCreation(r_line),
+                ShowCreation(a_dot),
+                FadeIn(a_text),
+                ShowCreation(r_text),
+            ),
+            run_time=2,
+        )
+
+        #3. make another r line
+        r_line2 = r_line.copy().next_to(circle.get_top(),UP)
+        line_text = TextMobject("a string equal to radius r").next_to(r_line2, UP)
+        self.play(
+            LaggedStart(
+                ShowCreation(line_text),
+                ShowCreation(r_line2),
+            ),
+            run_time=3,
+        )
+        self.play(r_line2.move_to, r_line.get_center(), run_time=1.5)
+        self.wait(0.5)
+        target = r_line2.generate_target()
+        target.shift(R * RIGHT)
+        self.play(
+            LaggedStart(
+                FadeOut(line_text),
+                MoveToTarget(r_line2),
+            ),
+            run_time=2,
+        )
+        self.wait()
+
+        #4. draw arc
+        B = circle.point_from_proportion(1 / (2 * PI))
+        arc = ArcBetweenPoints(A,B, angle=TAU/6, color=BLUE)
+        b_dot = Dot(color=BLUE).move_to(B)
+        b_text = TextMobject("B").next_to(B,RIGHT).shift(UP*0.1)
+        r2_text = r_text.copy().next_to(arc,RIGHT, buff=0.1).shift(UP*0.05)
+        self.play(
+            LaggedStart(
+                Transform(r_line2, arc),
+                ShowCreation(b_dot),
+                ShowCreation(b_text),
+                ShowCreation(r2_text),
+            ),
+            run_time=4,
+        )
+        self.wait()
+
+        #5 draw BO line
+        bo_line = Line(B, ORIGIN, color=BLUE)
+        r3_text = r_text.copy().next_to(bo_line, LEFT).shift(RIGHT*0.4)
+        self.play(
+            LaggedStart(
+                ShowCreation(bo_line),
+                ShowCreation(r3_text),
+            ),
+            run_time=2,
+        )
+
+        #6. radian
+        theta = ArcBetweenPoints(r_line.point_from_proportion(0.2), bo_line.point_from_proportion(1-0.2),color=YELLOW)
+        radian_text = TextMobject("1 radian", color=YELLOW).scale(0.7).next_to(theta,RIGHT).shift(LEFT*0.15+UP*0.1)
+        self.play(
+            LaggedStart(
+                ShowCreation(theta),
+                ShowCreation(radian_text),
+            ),
+            run_time=2,
+        )
+        self.wait()