Take a copper ring that looks like an O and cut a segment so it looks like the letter C Would the gap grow wider or more narrow as the metal expands if you were to heat the metal and explain?

Answer 1

You answered your own question with "as the metal expands." The gap stays proportionally the same, because the whole piece of copper expands when it is heated. It isn't relevant that someone cut out a piece of it, because the copper is completely unaware of this. It expands because you heated it, causing its atoms to move apart. This expansion occurs everywhere in the copper, but obviously not in the gap (there's nothing there but air). You may be thinking something like, "Well then the copper must close the gap," but you have to remember that ALL of the copper expands. You get a bigger version of what you had before you heated it. Tight pipe and machinery fittings are accomplished using this method. Heat it to expand, cool it to shrink.

Answer 2

The gap where the segment was cut would grow wider as the metal expands from heating. When metal is heated, it expands uniformly in all directions, causing the gap to widen. Conversely, when the metal cools, the gap would narrow as the metal contracts.