http://www.youtube.com/watch?v=AK4WHbm6q3c&sns=em

I was playing around with the physics stuff and got a nice simulation, only to find that after a few iterations it starts going really slowly. But it’s not doing anything different so somewhere it is accumulatong a drag. How do I get rid of that?

Video above, code below.

```
-- Use this function to perform your initial setup
displayMode(FULLSCREEN)
function setup()
sand = {}
scalefactor = 2
radius = 7
nradius = 2
gap = 2*(radius+nradius+5)
grains = 0
watch("grains")
mgrains = 100
w = 200
h = 300
x = - w/2
y = - h/2
ground = {physics.body(POLYGON,
vec2(x,y+20),
vec2(x,y),
vec2(x+w,y),
vec2(x+w,y+20)),
physics.body(POLYGON,
vec2(x,y+20),
vec2(x+20,y+20),
vec2(x+20,y+h-20),
vec2(x,y+h-20)),
physics.body(POLYGON,
vec2(x+w,y+20),
vec2(x+w-20,y+20),
vec2(x+w-20,y+h-20),
vec2(x+w,y+h-20)),
physics.body(POLYGON,
vec2(x+w,y+h-20),
vec2(x+w,y+h),
vec2(x,y+h),
vec2(x,y+h-20)),
physics.body(POLYGON,
vec2(x+20+gap,y+h/2+40),
vec2(x+w-20-gap,y+h/2-30),
vec2(x+w-20-gap,y+h/2-40),
vec2(x+20+gap,y+h/2+30)
)
}
for k,v in ipairs(ground) do
v.type = STATIC
v.restitution = .5
end
t = 0
physics.gravity(vec2(0,0))
physics.iterations(1,1)
flip = 1
gstrength = .5
--startRecording()
end
-- This function gets called once every frame
function draw()
-- This sets a dark background color
background(40, 40, 50)
translate(WIDTH/2,HEIGHT/2)
scale(2)
-- This sets the line thickness
strokeWidth(20)
stroke(0, 76, 255, 255)
noFill()
rect(x,y,w,h)
noStroke()
ellipseMode(RADIUS)
-- Do your drawing here
local a = 10*vec2(UserAcceleration.x,UserAcceleration.y)
local g = flip*gstrength*vec2(Gravity.x,Gravity.y)
for k,v in ipairs(sand) do
fill(191 + 64*v.info.gdir, 0, 0, 255)
ellipse(v.x,v.y,v.radius)
v:applyForce(a + v.info.gdir*g)
end
if grains < mgrains then
if ElapsedTime - t > .1 then
t = ElapsedTime
grains = grains + 1
addGrain()
end
end
end
function addGrain()
local s =
physics.body(CIRCLE,
radius - nradius+ 2*nradius*math.random()*math.random())
s.x = math.random(x+40,x+w-40)
s.friction = 0
s.info = {}
if math.random() < .5 then
s.info.gdir = -1
s.y = y+3*h/4
else
s.info.gdir = 1
s.y = y+h/4
end
table.insert(sand,s)
end
function touched(touch)
if touch.tapCount == 2 then
--stopRecording()
end
if touch.state == BEGAN then
flip = - flip
end
end
```

tap screen to flip gravity.