CustomScrollView.m

//get velocity from pan gesture
CGPoint velocity = [panGestureRecognizer velocityInView:self];
if (self.bounds.size.width >= self.contentSize.width) {
    //make movement zero along x if no horizontal scrolling
    velocity.x = 0;
}
if (self.bounds.size.height >= self.contentSize.height) {
    //make movement zero along y if no vertical scrolling
    velocity.y = 0;
}

//we need the negative velocity of what we get from the pan gesture, so flip the signs
velocity.x = -velocity.x;
velocity.y = -velocity.y;

POPDecayAnimation *decayAnimation = [POPDecayAnimation animation];

POPAnimatableProperty *prop = [POPAnimatableProperty propertyWithName:@"com.rounak.boundsY" initializer:^(POPMutableAnimatableProperty *prop) {
    // read value, feed data to Pop
    prop.readBlock = ^(id obj, CGFloat values[]) {
        values[0] = [obj bounds].origin.x;
        values[1] = [obj bounds].origin.y;
    };
    // write value, get data from Pop, and apply it to the view
    prop.writeBlock = ^(id obj, const CGFloat values[]) {
        CGRect tempBounds = [obj bounds];
        tempBounds.origin.x = values[0];
        tempBounds.origin.y = values[1];
        [obj setBounds:tempBounds];
    };
    // dynamics threshold
    prop.threshold = 0.01;
}];

decayAnimation.property = prop;
decayAnimation.velocity = [NSValue valueWithCGPoint:velocity];
[self pop_addAnimation:decayAnimation forKey:@"decelerate"];