;; $Id: grav-force.scm,v 1.6 2002/04/09 22:25:24 leavens Exp $

;;; AUTHOR:  Gary T. Leavens

;;	GRAVITATIONAL FORCE EXAMPLE
	
(define G
  ;; UNITS: N * m^2 / kg^2
  6.670e-11)

(define square
  ;; UNITS: (-> (m) m^2)
  (lambda (r) (* r r)))

(define grav-force
  ;; UNITS: (-> (kg m kg) N)
  (lambda (m1 r m2)	
    (if (zero? r) 
	0.0
	(/ (* G (* m1 m2))
	   (square r)))))

(define grav-force-c 
  ;; UNITS: (-> (kg)
  ;;           (-> (m)
  ;;               (-> (kg)
  ;;                   N)))
  (lambda (m1)			; kg 
    (lambda (r)			; m
      (lambda (m2)		; kg 
          (if (zero? r) 
	      0.0
              (/ (* G (* m1 m2))
	         (square r)))))))

      
;;		USING IT

(define mass-of-earth
  ;; UNITS: kg
  5.96e24)

(define radius-of-earth
  ;; UNITS: m
  6.37e6)

(define earths-force
  ;; UNITS: (-> (m) (-> (kg) N))
  (grav-force-c mass-of-earth))

(define force-at-surface
  ;; UNITS: (-> (kg) N)
  (earths-force radius-of-earth))