Final answer:
Running hot water over a tight metal lid on a glass jar helps because the hot water causes the metal lid to expand more than the glass jar, making it easier to open. The higher coefficient of expansion of metals compared to glass is key here. Although in practice, wet surfaces could make it difficult to grip the lid and the jar.
Step-by-step explanation:
Yes, running hot water over a tight metal lid on a glass jar before trying to open it can be helpful. This effectiveness stems from the fact that metals typically have a higher coefficient of thermal expansion compared to glass. As a result, when the lid is exposed to hot water, it expands slightly more than the glass jar does.
This small expansion of the metal lid relative to the jar can create enough extra space to make the lid easier to unscrew. However, one should note that in practice, getting the lid and jar wet might make gripping them more challenging unless you dry them or use a cloth to improve grip.
When inserting a metal peg into a hole in a metal block, the correct temperature difference can ensure a tight fit. If the metal block is hotter than the peg, it will expand, allowing the slightly larger peg to be inserted. Once the temperatures equalize, the peg will remain tightly fitted within the block.
Liquids and solids generally expand with increasing temperature because of increased kinetic energy of their atoms and molecules. However, some materials exhibit anomalous behavior, known as negative thermal expansion, and they actually shrink with an increase in temperature. This unusual behavior is due to the unique structure or bonding characteristics within the material that cause it to contract when heated.