How to make a body move upward using lua with corona sdk?

Question

This is my object which i want to give upward velocity

local myImage = display.newImage( "rose.png" )
myImage.x = 320
myImage.y = 500
myImage.rotation = 0
physics.addBody( myImage, { density=0.1, friction=2.0, bounce=0.0,velocity=-40 } )

Function to give upward velocity

local function test()
myImage:setLinearVelocity(0, -20)
end
test()

The object is not moving upward and this is my physics:

adding Physics
local physics =require("physics")
physics.setGravity(0,0.9)
physics.start()

Answer 1

Your object's linear velocity is being affected by gravity. You can either set the linear velocity every frame with a Runtime enterFrame listener, or you could turn off gravity for your myImage object with:

myImage.gravityScale = 0

After you add the physics body.

Answer 2

尝试将重力的y值设置为负数。

physics.setGravity(0, -0.98)