With our image view responding to gravity and our screen bounds we can start detecting collisions. You may have noticed that when the image view is falling, it falls right through our two labels below it.

This is because UIKit Dynamics will only respond to UIView elements that have been assigned behaviors. Each behavior can be assigned to multiple objects, and each object can have multiple behaviors. Because our labels have no behaviors associated with them, the UIKit Dynamics physics engine simply ignores it.

Let's make the food image view collide with the date label. To do this, we simply need to add the label to the collision behavior allocation call. Here is what the new code looks like:

collision = [[UICollisionBehavior alloc] initWithItems:@[self.foodImageView, self.foodDateLabel]];

As you can see, all we have done is add self.foodDateLabel to the initWithItems array property. As mentioned before, any single behavior can be associated with multiple items. Run your code and see...