Bridges

Essential Question
How do people build stronger and more efficient bridges?

Objectives

 * Recognize and apply different designs as related to function of bridges.
 * Model different existing styles of bridges.

Introduction & Student Background
What kind of bridges exist in your neighborhood, town, or city? How busy are they, how many cars pass on them? How does this impact their design, and what factors and/or problems should they design with in mind? How sturdy/secure do each one of these bridges have to be, depending on their size, and height/length? What resource limitations are people working under?

In this activity, students will use plastic disposable straws of various lengths, and tape to build a model bridge. They must build across a fixed distance and have a certain width. The bridge will then be tested by adding a weight to the center of the bridge and seeing how much weight the bridge can support.

Vocabulary
''Note: Students do not necessarily need to know these building concepts to do the activity. If you want to and have the time to involve the students in more actual physics and construction, then introduce these ahead of time. ''

Efficiency: the mass of the load or weight held, divided by the mass of the bridge

Level: The evenness of the base. If the base of the tower is not even then everything built subsequently is not balanced.

Tension: the pulling force of a string, cable, or in this case, straw.

Compression: The opposite of tension. A pushing force (balanced inward).

Materials

 * Plastic (soda) straws
 * Scissors
 * Scotch/clear tape
 * Masking tape
 * String/Yarn
 * Ruler(s)
 * Bucket
 * Sand (or other pourable material)
 * Containers for straws.

PREP

 * 1) Divide the plastic soda straws in half. Leave one half alone, and cut the straws in the other group in half.
 * 2) optional: print or otherwise obtain pictures of different buildings and bridges as examples of real-life application.
 * 3) Set out the different group of straws (in separate containers) and the tape in the center of the table.
 * 4) Use the ruler to measure out a set distance for the bridge to span. Either mark the distance using a length of masking tape on the table at a workspot or providing a ruler for the builder to use.
 * 5) Move two tables to each other so that the distance between them is slightly less than the set distance for the bridge. This will be the testing area.
 * 6) Tie the string to the bucket handle.

ACTIVITY

 * 1) Introduce the topic by asking students about what famous buildings and bridges they know of, and what kind of buildings are present in their local community/neighborhood. (see student background)
 * 2) Have students categorize different famous buildings and their functions.
 * 3) Make sure both ends of the bridge can be taped down to the end tables of the testing area. Move the bridge to the testing area after the student has completed construction and use masking tape to tape the bridge down.
 * 4) Loop the string around the center of the bridge (alternatively, use paper clip hooks tied to the string to hook onto the bridge?)
 * 5) Pour sand slowly into the bucket until the bridge collapses, breaks, or falls.
 * 6) Measure the weight of the bucket on a scale, OR by number of sand scoops.

How it fits to Standard

 * Use simple tools and materials to solve problems in a creative way (K-1)
 * Develop a solution to a problem by using a simplified technological design process. Investigate the use of tools. (2-3)

Follow Up
What types of structures worked well? Which structure was the most efficient (use of straws versus function?)