Final answer:
The incorrect step in fabricating a mouth protector is using a mouth guard that is too loose or too tight. For a snug fit when inserting a metal peg into a block, the block should be hotter to allow expansion. Running hot water over a jar lid helps remove it by expanding the lid more than the glass.
Step-by-step explanation:
The question relates to the incorrect step in fabricating a mouth protector. Among the listed options, using a mouth guard that is too loose or too tight is an incorrect step because it will not provide the proper fit necessary for protection and comfort. The correct steps involve heating the mouth guard to soften it, molding it to fit the individual's teeth and bite, and then cooling it down to set the shape.
Now, to answer the referenced physics questions:
- The block should be hotter than the peg during insertion, since heating the block will cause it to expand, making the hole larger and allowing the ideally slightly larger cold peg to be inserted. Once the temperatures equalize, the peg will fit snugly within the block.
- Running hot water over a tight metal lid on a glass jar does help to open it. The heat causes the metal lid to expand more than the glass, loosening the seal and making it easier to twist off.
- Liquids and solids usually expand with increasing temperature due to increased kinetic energy. However, anomalous expansion can occur when a material's structure is altered in a way that results in a decrease in overall volume with increasing temperature.