Lua - Gravity

local physics=require("physics")
physics.start()
physics.setGravity(0,9.8)

local ball=display.newImage("ball2.png")
ball.x=display.contentWidth/2

physics.addBody(ball)

local floor=display.newImage("floor.png")
floor.y=display.contentHeight-10
floor.x=display.contentWidth/2

physics.addBody(floor,"static")