local PTM_RATIO = 32.0

    local gravity = b2Vec2(0.0, -10.0)
    local _world = b2World:new_local(gravity)

    
    -- Create edges around the entire screen
    local groundBodyDef = b2BodyDef:new_local()
    groundBodyDef.position = b2Vec2(0, 0)
    local groundBody = _world:CreateBody(groundBodyDef)


    local groundEdge = b2EdgeShape:new_local()
    local boxShapeDef = b2FixtureDef:new_local()
    boxShapeDef.shape = groundEdge

    groundEdge:Set(b2Vec2(0,0), b2Vec2(winSize.width/PTM_RATIO, 0))
    groundBody:CreateFixture(boxShapeDef)

    groundEdge:Set(b2Vec2(0,0), b2Vec2(0, winSize.height/PTM_RATIO))
    groundBody:CreateFixture(boxShapeDef)

    groundEdge:Set(b2Vec2(0, winSize.height/PTM_RATIO), b2Vec2(winSize.width/PTM_RATIO, winSize.height/PTM_RATIO))
    groundBody:CreateFixture(boxShapeDef)

    groundEdge:Set(b2Vec2(winSize.width/PTM_RATIO, winSize.height/PTM_RATIO), b2Vec2(winSize.width/PTM_RATIO, 0))
    groundBody:CreateFixture(boxShapeDef)

        -- Create body and shape
        local bodyDef = b2BodyDef:new_local()
        bodyDef.type = b2_dynamicBody
        bodyDef.position:Set(x/PTM_RATIO, y/PTM_RATIO)
        bodyDef.userData = bodySprite
        local _body = _world:CreateBody(bodyDef)
 
        local circle = b2CircleShape:new_local()
        circle.m_radius = 26.0/PTM_RATIO
 
        shapeDef = b2FixtureDef:new_local()
        shapeDef.shape = circle
        shapeDef.density = 1.0
        shapeDef.friction = 0.2
        shapeDef.restitution = 0.8
        _body:CreateFixture(shapeDef)

        table.insert(body_list, _body)

    -- tick
    local function tick(dt)
        _world:Step(dt, 10, 10)
        if body_list ~= nil then
            for i, body in ipairs(body_list) do
                    local sprite = sprite_list[i]
                    sprite:setPosition(b2Vec2(body:GetPosition().x * PTM_RATIO, body:GetPosition().y * PTM_RATIO))
                    sprite:setRotation(-1 * CC_RADIANS_TO_DEGREES(body:GetAngle()))
            end
        end
    end

    CCDirector:sharedDirector():getScheduler():scheduleScriptFunc(tick, 0, false)