Jennifer Swanson - Bridges!: With 25 Science Projects for Kids

Titles in the Explore Engineering Set

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Imagine that youre sitting on the school bus, on your way to school. As the bus bounces along the road, you look up. Huge steel bars and cables rise up around you toward the sky. You tip your head back to see how high they go. What are you looking at? Parts of a bridge ! Look down and youll notice that the bus is crossing something, such as a river.

Bridges connect things. They allow people to move from one place to another more easily. A bridge can cross a road, a narrow valley, or even a body of water.

WORDS TO KNOW

steel: a hard, strong material made of iron combined with other elements.

bridge: a structure built to cross something that blocks your way, such as a river, bay, road, railway, or valley.

canyon: a deep trench in the earth, often with steep sides.

BCE: put after a date, BCE stands for Before Common Era and counts down to zero. CE stands for Common Era and counts up from zero. These nonreligious terms correspond to BC and AD. This book was printed in 2018 CE.

goods: items, such as food and clothing, that people can buy and sell.

arch: a curved structure in the shape of an upside-down U or semi-circle.

engineer: a person who uses science, math, and creativity to design and build things.

iron: a strong, hard, magnetic metal.

span: to stretch from side to side of something. Also, the distance between two things.

Bridges pass over lakes and rivers, connect mountains, and cross canyons . There is even a bridge across the Grand Canyon!

Bridges have been around for thousands of years. The ancient Romans first built bridges in the second century BCE . They were built to allow people to cross rivers to trade goods and tell each other news. Roman armies needed these bridges to move from one place to another.

The Romans mostly built bridges using arches to support them. At first, Roman engineers used stone blocks that were held together with iron clamps. These bridges were large and heavy, though, and couldnt span long distances.

The Romans tried using other materials. They mixed broken bits of stone with clay, sand, and water to create something that hardened when it dried, even under water.

What had they invented? The first concrete , which they used to build bridges. Concrete bridges faced with stone were much stronger and easier to build. These bridges also lasted a lot longer. Hundreds of Roman bridges built during and after the second century BCE are still standing.

WORDS TO KNOW

concrete: a hard construction material made with cement, sand, and water.

BRIDGE STRUCTURES TODAY

There are six basic bridge structures in use today. These include beam, truss, arch, cantilever, suspension, and cable. Each type of bridge has a different purpose. Some are stronger than others, some can fit into smaller areas of land, and some just look nicer. Each bridge design is carefully selected for the area where it will stand, what it will carry, and how far it must span.

Have you ever seen a picture of a famous bridge, such as the Golden Gate Bridge in San Francisco or maybe the Sydney Harbour Bridge in Australia? How were these bridges constructed?

THE SYDNEY HARBOUR BRIDGE

WORDS TO KNOW

prototype: a model of something that allows engineers to test their ideas.

GOOD ENGINEERING PRACTICES

Engineers and scientists keep their ideas organized in notebooks. Engineers use the engineering design process to keep track of their inventions, and scientists use the scientific method to keep track of experiments.

As you read through this book and do the activities, record your observations, data, and designs in an engineering design worksheet or a scientific method worksheet. When doing an activity, remember that there is no right answer or right way to approach a project. Be creative and have fun!