Question

Considering how solids act when they are heated and cooled, why do you think they put flexible connections in the road on a bridge?

Answer 1

These expansion joints are placed in the roadway to allow for the thermal expansion of the concrete or what ever material is used.

Explanation:

The amount of expansion and contraction that occurs between the high heat of summer and the depths of winter will cause materials to expand and contract in proportion to their length.

For concrete, the expansion amounts to about one part in `10^-5` per °C, which translates into only one centimeter over a distance of a kilometer for each 1°C temperature increase. Even still, room must be given to allow for this, or the roadway would buckle as the temperature rose from (say) -10°C to +30°C, or pull apart as the temperature fell.