--if you don't need to insert more balls at a later point, you can use this method of storing them.
local balls = {} --creates empty array.
 
balls[1] = display.newCircle( 100, 100, 30 )
balls[2] = display.newCircle( 100, 100, 30 )
balls[3] = display.newCircle( 100, 100, 30 )
balls[4] = display.newCircle( 100, 100, 30 )
 
--4 balls now in the array, now to reference them.
 
for i = 1, #balls do --starts at 1 and goes through all the values in your array. #balls = 4.
        
        --reference using i, means every ball in array is effected as you're not using direct reference such as balls[1] or balls[2]
        -- you're using a value that incrememnts every time the loop goes round.
        
        --makes every ball a different colour.
        balls[i]:setFillColor( i*55, 255-i*55, 220 )
        
        balls[i].x = 160
        balls[i].y = 100 * i
 
        print("i is now: " .. i)
 
end
 
--so in your touch listner for moving balls you would use ball[i] instead of ball. 
 
--look at the drag body sample code, in the sample code folder.