semi-stable physics engine

0 rem I started writing this program on march 24, And tried to fix collision detection for 2 months, And failed.
0 rem So i present to you - 2 months late - A broken physics engine

10 hgr2
20 R = 10 : rem Radius of ball.
30 X = 30 : Y = 10 : rem Ball starting positions
40 G = 0.2 : rem Gravity
50 T = 4 : rem Terminal velocity


60 C = 1.5

210 Poke 230,32 : gosub 300 : Poke 49236,0 : poke 230,64 : gosub 300 : poke 49237,0 : goto 210
300 hcolor = 0 : hplot 0,0 : call -3082

310 Hcolor = 3 : hplot 0,0 to 80,191 : hplot 279,0 to 200,191 : hplot 0,100 to 279,191 : hplot 279,100 to 0,191

320 hcolor = 6 : for ch = 0 to 6.28 step 0.1
325 if hscrn(sin(ch)*r+x,cos(ch)*r+y) = 3 then vx = vx - sin(ch)*c : vy = vy - cos(ch)*c
330 next
340 for ch = 0 to 6.28 step 0.1 : hplot sin(ch)*r+x,cos(ch)*r+y : next : x = x + vx : vy = vy + g : y = y + vy
350 if vx > t then vx = t
360 if vy > t then vy = t
370 if vx < -t then vx = -t
380 if vy < -t then vy = -t
390 return

400 return