Exam 2 key 2011 - Avian Biology Exam#2 Key Spring 2011...

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Avian Biology Exam #2 Key Spring 2011 1a) (Doug graded) Profile drag is the force associated with pushing air aside as a bird’s body moves through the air. Induced drag is created by air “slipping” from the high pressure area under the wing, around the tip of the wing, to the area of low pressure on top of the wing, creating swirling pockets of air behind the wingtips and taking energy in the process. b) The end of the fan is bent upwards to block the flow of air around the tip of the blade, and hence to reduce induced drag. This design feature will make the fan blades turn with less force (less electricity). You may recall an example from lecture in which the wingtips of some airplanes are bent upwards in a similar way, for an identical reason. c) The blades are pointed. This reduces induced drag in two ways, which are related to each other. First, the small airfoil at the end of the blade results in very little pressure difference between the front and back of the blade, reducing the tendency of air to flow around the tip from the area of high to low pressure. Second, the very small point of the blade means that there is a very small area for air to flow around. Hence, the energy-zapping swirls of air (drag on the turning of the blades) are very much reduced. 2a) (Doug graded) Your power curve should have looked something like this: (b) At low velocities, birds that fly in the air require far more power because the force of gravity is so much stronger than the upward on penguins. This means that flying birds in the air must expend a lot of energy flapping their wings hard enough to counter the force of gravity. Note, in particular, how quickly the power curve you drew in part “a” rises as velocity approaches zero. (c) At high velocities, both types of birds encounter problems with drag. However, because water is so much denser than air, profile drag will be much higher for penguins – they will have to expend far more energy to move quickly. 3a) (Doug graded) Smaller clutches are typically selected for when nest predation is high because fewer eggs and young in the nest mean that the number of feeding trips is reduced, the noise of nestlings is reduced, and the total time of eggs and young in the nest is reduced. All of these will potentially lessen the chance a predator will find the nest. Even if a predator does find the nest, less investment in eggs and young by
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Exam 2 key 2011 - Avian Biology Exam#2 Key Spring 2011...

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