add air drag.

1 files changed, 5 insertions, 1 deletions

diff --git a/dat.h b/dat.h
index 24799b8..da2038d 100644
--- a/dat.h
+++ b/dat.h
@@ -1,4 +1,6 @@
-#define Eg	9.81
+#define Eg	9.81	/* earth's gravity (m·s⁻²) */
+#define Cd	0.45	/* drag coefficient for a sphere */
+#define ρ	1.293	/* air density (kg·m⁻³) */
 #define PIX2M	0.001
 #define M2PIX	(1.0/PIX2M)
 
@@ -6,6 +8,7 @@ enum {
 	Stheta = 0,
 	Spos,
 	Svel,
+	Sdrag,
 	Sdeltax,
 	Seta,
 	SLEN,
@@ -17,4 +20,5 @@ struct Projectile
 {
 	Point2 p, v;
 	double mass;
+	double r;
 };