There was, if I am not mistaken, an episode of I Love Lucy wherein Lucy manages to get her head stuck in a metal teakettle. Ethel jokingly (I hope!) suggests that she put her head in the oven to heat up the metal so it will expand and she can fit her head out. A clever idea, not counting the fact that it would have unfortunate side effects for Lucy!
But we shouldn’t be so convinced it would work. Consider a piece of sheet metal with a circular hole punched out. Heated, the metal expands. The hole will either get larger or smaller – does the overall expansion cause the metal to expand away from the hole, or does the metal’s expansion force it into the space formerly occupied by the emptiness of the hole?
Or what if it’s not a circle? Does the shape of the hole make a difference?
I like to poll my students on this. The split is usually pretty even between the larger and smaller schools of thought, at least among those who haven’t had engineering classes that might have already told them the answer. The neat thing about science is that you don’t have to decide which school of thought to believe, and the numbers of people who think one way or another are absolutely irrelevant. Instead, you can check your idea against first principles and then check your check via experiment.
Here’s a hint. Think of the atoms of the material as though they were arranged in a neat grid. Thermal expansion makes the grid spacing larger. If there’s a gap in the grid, what happens to its size as the grid spacing increases?
And should you want to see the answer for yourself experimentally (you should!), I’ve found a site that actually has video of the experiment.