Animation starts slowly and get faster with time ios Swift
<p>i am trying to animate the rotation of an imageview. it is rotating and animating but my animation start slowly and it speed up with time
lets say i am performing animation with 5 seconds duration then first 1-2 seconds my image is rotating slowly but as time gets closer to 5 it speeds up here is my code</p>

<pre><code>UIView.animateWithDuration(5.0, delay:0 , options: .Repeat , animations: {
//fan is UIImageView
        self.fan.transform = CGAffineTransformMakeRotation((180.0 * CGFloat(M_PI)) / 180.0)
    }, completion: nil) 
</code></pre>