Data commit

Task/Animate-a-pendulum/Racket/animate-a-pendulum.rkt

@@ -0,0 +1,19 @@
+#lang racket
+
+(require 2htdp/image 2htdp/universe)
+
+(define (pendulum)
+  (define (accel θ) (- (sin θ)))
+  (define θ (/ pi 2.5))
+  (define θ′ 0)
+  (define θ′′ (accel (/ pi 2.5)))
+  (define (x θ) (+ 200 (* 150 (sin θ))))
+  (define (y θ) (* 150 (cos θ)))
+  (λ (n)
+    (define p-image (underlay/xy (add-line (empty-scene 400 200) 200 0 (x θ) (y θ) "black")
+                                 (- (x θ) 5) (- (y θ) 5) (circle 5 "solid" "blue")))
+    (set! θ (+ θ (* θ′ 0.04)))
+    (set! θ′ (+ θ′ (* (accel θ) 0.04)))
+    p-image))
+
+(animate (pendulum))