****WATER BUOYANCY EXAMPLE****

IF YOU HAVE SIMULATOR OF CORONA SDK THEN ITS GREAT: OR DOWNLOAD IT FROM THIS LINK. http://developer.coronalabs.com/user/register?destination=downloads/coronasdk
And complete the process. ITS EASY.
STEPS TO RUN THE CODE.
1. START NOTEPAD.
2. PASTE THE CODE.
3. OPEN FILE MENU AND CLICK ON SAVE AS.
4. GIVE NAME AS main.lua AND Select ALL FILE just below the SAVE AS OPTION.
5. NOW OPEN THIS FILE main.lua IN SIMULATOR.



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---------------------- *** WATER BUOYANCY EXAMPLE ***  --------------------------
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-- HIDE STATUS BAR

display.setStatusBar(display.HiddenStatusBar)


-- INIT PHYSICS
local physics = require("physics")
physics.start()
physics.setGravity( 0, 40 )

local gx, gy = physics.getGravity()


-- FORWARD REFS

local _W = display.contentWidth
local _H = display.contentHeight

local ground, ceiling, leftWall, rightWall

local liquidLevel


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-----------------------------------------  *** SETTINGS ***  ------------------------------------------
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local liquidDensity = 1.0     -- Sets the desnity of the liquid (e.g. 1.0 default = water, 2.5 = oil etc)

local numberOfBoxes = 5        -- Sets the number of boxes

local boxSize = 40             -- Sets the size of the boxes


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-- CREATE SCREEN BOUNDARY

display.newImage( "Logo.png", 0, 450 )

ground = display.newRect(0,0,_W,20)
ground.x = _W * 0.5; ground.y = _H + (ground.height * 0.5)

ceiling = display.newRect(0,0,_W,20);
ceiling.x = _W * 0.5; ceiling.y = 0 - (ceiling.height * 0.5)

leftWall = display.newRect(0,0,10,_H)
leftWall.x = 0 - (leftWall.width * 0.5); leftWall.y = _H * 0.5

rightWall = display.newRect(0,0,10,_H)
rightWall.x = _W + (rightWall.width * 0.5); rightWall.y = _H * 0.5

physics.addBody(ground, "static", {friction = 0.1})
physics.addBody(ceiling, "static", {friction = 0.1})
physics.addBody(leftWall, "static", {friction = 0.1})
physics.addBody(rightWall, "static", {friction = 0.1})


-- CREATE 'BOXES' DISPLAY GROUP & BOXES

-- A display group we can loop through -
-- works just like a table, but allows us to perform other display functions upon the boxes as well.
-- Be sure to use boxes.numChildren instead of #boxes when getting the number of boxes in the group,
-- but otherwise it works just like a table (which is really just an array)

local boxes = display.newGroup()


-- It adds that box to the 'boxes' display group

local function addBox()
   
        local box = display.newRect( boxes, 0, 0, boxSize, boxSize)
       
        box.x = math.random(50, _W - 50); box.y = math.random(50, _W / 3)
        box.area = box.height * box.width
        box.density = 3.0
        box.mass = box.area * box.density
       
        box:setFillColor( math.random(0,255), math.random(0,255), math.random(0,255) )
       
        physics.addBody( box, { density=3.0, friction=0.5 } )
   
end



-- CREATE SET NUMBER OF BOXES (DEFINED IN SETTINGS ABOVE)

for i=1, numberOfBoxes do
        addBox()
end


-- CREATE LIQUID

local liquid = display.newRect(0, 0, _W, _H * 0.5)

liquid:setFillColor(0, 102, 255)
liquid.alpha = 0.3
liquid:setReferencePoint(display.TopCenterReferencePoint)
liquid.x = _W * 0.5
liquid.y = _H * 0.5


-- TOUCH TO DRAG FUNCTION
               
local function dragBody(e)
        local body = e.target
        local phase = e.phase
        local stage = display.getCurrentStage()
       
        if(phase == "began") then
                stage:setFocus(body, e.id)
                body.isFocus = true
                body.tempJoint = physics.newJoint("touch", body, e.x, e.y)
        elseif(phase == "moved") then
                if(body.tempJoint ~= nil) then
                        body.tempJoint:setTarget(e.x, e.y)
                end
        elseif(phase == "ended" or phase == "cancelled") then
                if(body.tempJoint ~= nil) then
                        stage:setFocus(body, nil)
                        body.isFocus = false
                        body.tempJoint:removeSelf()
                        body.tempJoint = nil
                end
        end

        return true
end


-- LOOP TO MAKE ALL BOXES DRAGGABLE

for i=1, boxes.numChildren do
        boxes[i]:addEventListener("touch", dragBody)
end


-- FLOAT/BUOYANCY FUNCTION

local function float()
        for i=1, boxes.numChildren do -- LOOP TO APPLY FORCES TO EACH BOX INDIVIDUALLY
               
                -- get the box from the display group
                local box = boxes[i]
               
                -- apply forces to box
                if (box.y + (box.height * 0.5)) >= liquid.y then
                       
                        local submergedPercent = math.floor (100 - (((liquid.y - box.y + (box.height * 0.5)) / box.height) * 100))
                       
                        if submergedPercent > 100 then
                                submergedPercent = 100
                        end
                       
                        if submergedPercent > 40 then
                               
                                local buoyancyForce = (box.mass * gy)
                                box:applyForce( 0, buoyancyForce * -0.002, box.x, box.y )
                               
                                box.linearDamping = 4 * liquidDensity
                                box.angularDamping = 5 * liquidDensity
                        else
                                box.linearDamping = 0
                                box.angularDamping = 0
                        end    
                end    
        end    
end

Runtime:addEventListener( "enterFrame", float )