How Do Bridges Stand Up Without Falling Down?

Bridges stay up because they are really good at sharing the weight. Imagine a long stick resting on two trees. If you stand in the middle, it bends down. But if you push its ends together tight, or tie strings to hold it up, it stays straight! Bridges use these same tricks with metal and stone.

Every bridge has parts that get squeezed (called compression) and parts that get stretched (called tension). Stone bridges love being squeezed. Metal bridges love being pulled tight.

You might have seen big triangles on the sides of a bridge. These are called trusses. A triangle is the strongest shape because it cannot squish into a square unless its sides break. They spread the weight from cars and trains all over to the ground safely.