Animate a pendulum: Difference between revisions

(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)))