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Chapter 17: Problem 20

For food storage, what is the advantage of placing a metal lid on a glass jar? (Hint: Why does running the metal lid under hot water for a minute help you open such a jar?)

Short Answer

Expert verified
Question: Explain the advantage of using a metal lid on a glass jar for food storage and how running the metal lid under hot water can help open the jar. Answer: The advantage of using a metal lid on a glass jar for food storage is that it creates an airtight seal due to the higher rate of thermal expansion of metals, preventing the entry of air, contaminants, and microorganisms. Running the metal lid under hot water causes it to heat up and expand more than the glass, loosening the airtight seal and making it easier to open the jar.

Step by step solution

01

Identifying the materials and their properties

First, we need to identify the materials involved in this exercise: a metal lid and a glass jar. Metals generally have a higher rate of thermal expansion compared to glass. This means that metals expand more when heated and contract more when cooled compared to glass.
02

Understanding the advantage of a metal lid on a glass jar

Due to the higher rate of thermal expansion of metals, placing a metal lid on a glass jar creates an airtight seal as the metal lid contracts around the glass jar's opening when it cools down. This advantage prevents the entry of air, microorganisms, and any other contaminants, thus ensuring the food inside the jar is well-preserved.
03

Explaining the link between heating the metal lid and opening the jar

When the metal lid is placed under hot water, it heats up and expands. Since the metal expands more than the glass, loosening the airtight seal between the lid and the jar. This process makes it easier to open the jar, as it reduces the force required to break the seal between the lid and the jar.
04

Conclusion

In conclusion, the advantage of using a metal lid on a glass jar for food storage is the ability to create an airtight seal, which preserves the food inside by preventing the entry of contaminants. Running the metal lid under hot water helps to open the jar, as the expansion of the metal due to heating breaks the tight seal, thus making it easier to open.

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Most popular questions from this chapter

Which of the following bimetallic strips will exhibit the greatest sensitivity to temperature changes? That is, which one will bend the most as temperature increases? a) copper and steel b) steel and aluminum c) copper and aluminum d) aluminum and brass e) copper and brass

In a thermometer manufacturing plant, a type of mercury thermometer is built at room temperature \(\left(20^{\circ} \mathrm{C}\right)\) to measure temperatures in the \(20^{\circ} \mathrm{C}\) to \(70^{\circ} \mathrm{C}\) range, with \(\mathrm{a}\) \(1-\mathrm{cm}^{3}\) spherical reservoir at the bottom and a \(0.5-\mathrm{mm}\) inner diameter expansion tube. The wall thickness of the reservoir and tube is negligible, and the \(20^{\circ} \mathrm{C}\) mark is at the junction between the spherical reservoir and the tube. The tubes and reservoirs are made of fused silica, a transparent glass form of \(\mathrm{SiO}_{2}\) that has a very low linear expansion coefficient \((\alpha=\) \(\left.0.4 \cdot 10^{-6}{ }^{\circ} \mathrm{C}^{-1}\right) .\) By mistake, the material used for one batch of thermometers was quartz, a transparent crystalline form of \(\mathrm{SiO}_{2}\) with a much higher linear expansion coefficient \(\left(\alpha=12.3 \cdot 10^{-6}{ }^{\circ} \mathrm{C}^{-1}\right) .\) Will the manufacturer have to scrap the batch, or will the thermometers work fine, within the expected uncertainty of \(5 \%\) in reading the temperature? The volume expansion coefficient of mercury is \(\beta=181 \cdot 10^{-6}{ }^{\circ} \mathrm{C}^{-1}\).

In order to create a tight fit between two metal parts, machinists sometimes make the interior part larger than the hole into which it will fit and then either cool the interior part or heat the exterior part until they fogether. Suppose an aluminum rod with diameter \(D_{1}\) (at \(\left.2.0 \cdot 10^{1}{ }^{\circ} \mathrm{C}\right)\) is to be fit into a hole in a brass plate that has a diameter \(D_{2}=10.000 \mathrm{~mm}\) (at \(\left.2.0 \cdot 10^{1}{ }^{\circ} \mathrm{C}\right) .\) The machinists can cool the rod to \(77.0 \mathrm{~K}\) by immersing it in liquid nitrogen. What is the largest possible diameter that the rod can have at \(2.0 \cdot 10^{1}{ }^{\circ} \mathrm{C}\) and just fit into the hole if the rod is cooled to \(77.0 \mathrm{~K}\) and the brass plate is left at \(2.0 \cdot 10^{1}{ }^{\circ} \mathrm{C} ?\) The linear expansion coefficients for aluminum and brass are \(22 \cdot 10^{-6}{ }^{\circ} \mathrm{C}^{-1}\) and \(19 \cdot 10^{-6}{ }^{\circ} \mathrm{C}^{-1}\), respectively.

Which air temperature feels coldest? a) \(-40^{\circ} \mathrm{C}\) c) \(233 \mathrm{~K}\) b) \(-40^{\circ} \mathrm{F}\) d) All three are equal.

Even though steel has a relatively low linear expansion coefficient \(\left(\alpha_{\text {steel }}=13 \cdot 10^{-6}{ }^{\circ} \mathrm{C}^{-1}\right),\) the expansion of steel railroad tracks can potentially create significant problems on very hot summer days. To accommodate for the thermal expansion, a gap is left between consecutive sections of the track. If each section is \(25.0 \mathrm{~m}\) long at \(20.0{ }^{\circ} \mathrm{C}\) and the gap between sections is \(10.0 \mathrm{~mm}\) wide, what is the highest temperature the tracks can take before the expansion creates compressive forces between sections?
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