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Chapter 18: Problem 17

Why is a dry, fluffy coat a better insulator than the same coat when it is wet?

Short Answer

Expert verified
Answer: A dry, fluffy coat is a better insulator because it contains numerous air pockets that resist the flow of heat. When the coat becomes wet, water molecules fill the air pockets and reduce the coat's insulating properties, as water is a better conductor of heat than air. The presence or absence of trapped air pockets significantly affects the insulating properties of the coat.

Step by step solution

01

Understanding insulation

Insulation is the process by which a material resists the flow of heat. Good insulators help keep heat in during cold temperatures and keep heat out during warm temperatures. The property of insulation is often determined by the composition of a material and how its structure affects heat transfer.
02

Explaining the role of air pockets and fluffy materials

Fluffy materials with many air pockets, such as the dry, fluffy coat, are excellent insulators because air itself is a poor conductor of heat. The trapped air pockets within the fluffy coat create a barrier that resists heat transfer, causing the coat to act as an effective insulator.
03

Discussing the impact of water on the coat's insulation properties

When the same fluffy coat becomes wet, the water molecules can fill the air pockets, reducing the space between fibers of the coat. Water is a better conductor of heat than air, which means it transfers heat more efficiently than trapped air. Consequently, when the air pockets are filled with water, the coat loses its insulating properties due to the increased heat transfer.
04

Comparing dry and wet coats

In summary, a dry, fluffy coat provides better insulation because it contains numerous air pockets that resist the flow of heat. On the other hand, when the coat becomes wet, the water molecules replace the insulating air pockets, making the coat less effective as an insulator. The key difference between the two situations lies in the presence or absence of trapped air pockets, which significantly affects the insulating properties of the coat.

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Most popular questions from this chapter

In one of your rigorous workout sessions, you lost \(150 \mathrm{~g}\) of water through evaporation. Assume that the amount of work done by your body was \(1.80 \cdot 10^{5} \mathrm{~J}\) and that the heat required to evaporate the water came from your body. a) Find the loss in internal energy of your body, assuming the latent heat of vaporization is \(2.42 \cdot 10^{6} \mathrm{~J} / \mathrm{kg}\). b) Determine the minimum number of food calories that must be consumed to replace the internal energy lost (1 food calorie \(=4186\) J).

An air-cooled motorcycle engine loses a significant amount of heat through thermal radiation according to the Stefan-Boltzmann equation. Assume that the ambient temperature is \(T_{0}=27^{\circ} \mathrm{C}(300 \mathrm{~K})\). Suppose the engine generates 15 hp \((11 \mathrm{~kW})\) of power and, due to several deep surface fins, has a surface area of \(A=0.50 \mathrm{~m}^{2}\). A shiny engine has an emissivity \(e=0.050\), whereas an engine that is painted black has \(e=0.95 .\) Determine the equilibrium temperatures for the black engine and the shiny engine. (Assume that radiation is the only mode by which heat is dissipated from the engine.)

A gas has an initial volume of \(2.00 \mathrm{~m}^{3}\). It is expanded to three times its original volume through a process for which \(P=\alpha V^{3},\) with \(\alpha=4.00 \mathrm{~N} / \mathrm{m}^{11} .\) How much work is done by the expanding gas?

The \(R\) factor for housing insulation gives the thermal resistance in units of \(\mathrm{ft}^{2}{ }^{\circ} \mathrm{F} \mathrm{h} / \mathrm{BTU}\). A good wall for harsh climates, corresponding to about 10.0 in of fiberglass, has \(R=40.0 \mathrm{ft}^{2}{ }^{\circ} \mathrm{F} \mathrm{h} / \mathrm{BTU}\) a) Determine the thermal resistance in SI units. b) Find the heat flow per square meter through a wall that has insulation with an \(R\) factor of 40.0 , with an outside temperature of \(-22.0^{\circ} \mathrm{C}\) and an inside temperature of \(23.0^{\circ} \mathrm{C}\)

A cryogenic storage container holds liquid helium, which boils at \(4.2 \mathrm{~K}\). Suppose a student painted the outer shell of the container black, turning it into a pseudoblackbody, and that the shell has an effective area of \(0.50 \mathrm{~m}^{2}\) and is at \(3.0 \cdot 10^{2} \mathrm{~K}\). a) Determine the rate of heat loss due to radiation. b) What is the rate at which the volume of the liquid helium in the container decreases as a result of boiling off? The latent heat of vaporization of liquid helium is \(20.9 \mathrm{~kJ} / \mathrm{kg} .\) The density of liquid helium is \(0.125 \mathrm{~kg} / \mathrm{L}\).
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