## An Interesting Puzzle On The Expansion Of Heated Metal - Question of the Week 2014 Summer Girls Special Part 3

Everyone knows that when you heat something up it expands. Well, almost everything, except water around the freezing point and a few other weird substances. One example of something that expands when heated is the brass plate shown in the photograph below.

The question this week involves the hole.

When the brass plate is heated up by the gas burner shown in the photograph, the hole will:

• (a) get bigger.
• (b) get smaller.
• (c) remain the same size.

Click Read More for the asnwer.

The answer is (a): the hole will get bigger. We can see this experimentally by performing two demonstrations using the hole and the ball seen in the photograph below.

First, we attempt to push the ball through the hole when the plate is cool (at room temperature).

The concept of linear thermal expansion indicates to us how the metal (or other solid material) expands when heated. In particular, the expansion occurs such that the distance between any two points on the metal plate increases by the same ratio - for example, the distance between two adjacent corners, between two diagonal corners, or a diameter across the hole. One method of expansion that is specifically excluded is that the brass could expand inward into the hole. The brass does not expand equally in all directions, such as inward into the hole.