Why does a bridge have gaps at regular intervals?
Any bridge will expand in hot weather- that is, grow longer – due to its particles absorbing energy. The increase in energy causes the particles to vibrate faster and more violently about their fixed positions, meaning there is more space between them. This is why you often see those metal “grates” or gaps, as you call them, at regular intervals. This allows them to expand, without cracking in the process, since the metal will push the two parts of the bridge apart as it expands as well. In winter, the opposite occurs. In other words, the particles have less energy and so the parts of the bridge contract i.e. become smaller – to a less noticeable degree than the expansion in summer. Once again, the metal “grate” allows the pieces of the bridge to get smaller without one part being ripped away from the other.
