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Chapter 9: Problem 152

A spherical block of dry ice at \(-79^{\circ} \mathrm{C}\) is exposed to atmospheric air at \(30^{\circ} \mathrm{C}\). The general direction in which the air moves in this situation is (a) horizontal (b) up \(\quad(c)\) down (d) recirculation around the sphere (e) no motion

Short Answer

Expert verified
Answer: (c) Down, as the cooler air molecules near the surface of the dry ice are denser and sink, pushing the warmer air molecules upward.

Step by step solution

01

Identify the temperature difference

There's a significant temperature difference between the dry ice (-79°C) and the atmospheric air (30°C). The air is warmer in comparison to the dry ice.
02

Understand the principle of convection

Convection is the transfer of heat within a fluid (in our case, air) due to the motion of the fluid. When air comes into contact with the dry ice, the air molecules near the surface of the dry ice lose energy and become cooler and denser. Because cool air is denser than warm air, it tends to sink.
03

Determine the direction of air flow

Due to the cooling effect of the dry ice, the air molecules nearest to it will become cooler and denser, causing them to sink. As these denser air molecules move downwards, they push the warmer air molecules, resulting in an upward flow of warm air. This sets up a continuous flow where cool air sinks and warm air rises.
04

Conclude the general direction of air movement

In conclusion, the general direction in which the air moves in this situation is: (c) down, as the cooler air molecules near the surface of the dry ice are denser and sink, pushing the warmer air molecules upward.

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Most popular questions from this chapter

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