local allBalls = {}

local function destroyBall(ball)
    allBalls[ball] = nil
    ball:removeSelf()
end

function newBall(x, y)
    local ball = display.newGroup()
        ball.x, ball.y = x, y
    ball.shadow = display.newImage(ball, "shadow.png")
        ball.shadow.x, ball.shadow.y = 3, 3
    ball.image = display.newImage(ball, "ball.png")
        ball.image.x, ball.image.y = 0, 0
    physics.addBody(ball, {bounce=0.6 ,radius=ball.image.width / 2})
    ball.isFixedRotation = true
    allBalls[ball] = ball
    ball.destroy = destroyBall
    return ball
end