The drinking bird. A popular novelty bird toy consists of two semievacuated glass chambers (the head and the body), which are connected by a glass tube as shown in Figure P16.58 (left). The head is covered with an absorbent coating, and the bottom chamber is partially filled with a liquid that has a boiling point near room temperature. The bird goes through a cycle illustrated in Figure P16.58 (right). The bird starts with all the liquid in the bottom chamber and is suspended at an off-center pivot point so that it leans slightly forward. Next the fluid rises slowly up the tube, which is open at the bottom but submerged in the fluid. The fluid reaches the top chamber, and the bird tips forward. Finally, at full tilt, the bottom of the tube breaks the surface and the liquid pours back into the bottom chamber. The bird then returns to the upright position, and the cycle repeats. (a) Is work done by this cyclic process? Is the bird a heat engine? Describe. (b) The bird dips its head in the water during the cycle. Why is that important for the toy’s operation?
Figure P16.58
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