A common trick for opening a stubborn lid on a jar is to run very hot water over the lid for a short time. This is because the coefficient of expansion for glass is less than that for steel. Glass expands less than steel when heated. This makes it easier to open the lid. Is this true or false
The Correct Answer and Explanation is :
The statement is true.
Here’s an explanation:
The trick of running hot water over the lid of a jar works based on the differences in the thermal expansion properties of glass and steel. When materials are heated, they expand. The degree to which they expand depends on their coefficient of thermal expansion (CTE), which is a measure of how much a material’s size changes with temperature.
Glass typically has a lower coefficient of thermal expansion compared to steel. This means that when heated, glass expands less than steel. So, when you apply hot water to the metal lid of a jar, the steel lid expands more than the glass jar. This difference in expansion can make it easier to loosen the lid.
Here’s why:
- Steel Lid Expansion: The metal lid expands more than the glass jar due to its higher CTE. This expansion of the lid can cause it to loosen slightly from the glass rim. The lid might even slightly “pop” as the metal expands faster than the glass, helping to break the seal.
- Effect on Sealing: When the steel lid expands, it might temporarily create a bit of extra space between the lid and the jar, reducing the grip and making it easier to twist off.
- Practical Consideration: Running hot water over the lid (as opposed to the entire jar) is more effective because it focuses on the metal lid, causing it to expand while the glass jar remains relatively unaffected.
In conclusion, the process works because of the different thermal expansion properties of glass and steel, which helps break the seal between the lid and the jar, making the lid easier to unscrew.