swift - UIKit dynamics slowing gravity -

i'm using uikit dynamics create falling object , wondering if slow gravity make ball fall slower on command. example, object falling, press button, ball falls slower. how go doing this? here code (p.s. added squareview above didn't include because it's irrelevant question)

var squareview: uiimageview! var gravity: uigravitybehavior! var animator: uidynamicanimator! var collision: uicollisionbehavior! func viewdidload() {     super.viewdidload()      animator = uidynamicanimator(referenceview: view)     gravity = uigravitybehavior(items: [squareview])     gravity.gravitydirection = cgvector(dx: 0.0, dy: 1.1)     animator.addbehavior(gravity) } 

i tried writing gravity.gravitydirection = cgvector(dx: 0.0, dy: 0.5) flung object across screen frantically don't know here.

you can change magnitude of gravity behavior. (alternatively, possibly can change drag of falling object giving uidynamicitembehavior resistance, haven't tried i'm not of it.)