Bridges and Forces

What Is a Bridge?

A bridge is a structure that lets people, cars, and trains cross over something like a river or a road. It holds up the weight of everything that moves across it. Bridges can be made from wood, steel, concrete, or even rope. Even though they look different, all bridges have one job: stay strong and safe.

How Forces Act on a Bridge

When something sits on a bridge, it pushes down. This push is called Gravity. The bridge must push back upward; this is called the Support Force. If the bridge can’t push back enough, it will bend or break.

Other forces can also act on a bridge:

• Wind can blow sideways, trying to push the bridge over.
• Water can flow under the bridge and push against its supports.
• Earthquakes shake the ground, moving the bridge in many directions.

Engineers design bridges so they can handle all these forces. They use strong shapes, like triangles, because triangles keep their shape even when pushed.

Types of Bridges

Type	How It Handles Forces
Beam Bridge	Uses long, sturdy beams that bend a little but stay strong.
Arch Bridge	The curved arch pushes the weight outward into strong supports on each side.
Suspension Bridge	Cables hang from tall towers, spreading the weight across many points.
Truss Bridge	A web of triangles spreads forces evenly throughout the bridge.

Each type uses clever shapes to keep the bridge safe. By understanding forces, engineers can build bridges that last for many years and help people travel safely.