Tacoma Narrows Bridge Lesson Plans
Science
Many Kinds of Bridges
Bridges of all types are amazing structures, and have been used
from the time of the earliest humans. They vary in complexity from
simple logs straddling streams to beautiful, highly technical modern
structures such as suspension bridges. The simplest beam bridges
span short distances, while fragilelooking suspension bridges span
the longest crossings. There are many factors to take into account
when building a bridge: the distance needing to be spanned, geographic
factors, cost, aesthetics, available materials and technical expertise.
All of these factors determine how bridges are built.
Lesson Objectives
As a result of this lesson, students will be able
to:
 Describe four common bridge types, including suspension, arch,
beam and truss.
 Understand some of the basic design considerations engineers
take into account when building bridges;
 Understand basic bridge building vocabulary;
 Understand the function of bridges in modern society.
Time: Two days or class periods, plus
a week at home to build their own bridge.
Materials Needed:
 PowerPoint slides of bridge types, list of bridge terms and
their definitions, plastic straws, pins and plastic containers.
Legos or other small blocks, strips of poster board 18 inches
long and 2 inches wide, and packages of individually wrapped stackable
candies, such as Starbursts are also required.
Lesson Steps
Day One:
1. Explain to students
that there are several important elements to be considered
before a bridge is built. These include the proposed location, the
strength needed, the costs involved, and how the bridge will look.
2. Explain that bridges need to withstand strong
natural forces such as wind, hurricanes, and earthquakes,
as well as supporting their own weight and the weight of cars and
trucks driving across them.
3. All bridges move, and therefore have
to be able to bend and flex with the forces of compression and tension
acting upon them. (Show students what those words mean by using your
hands, a braided rope, or paper creased in a simple accordion fold.)
4. Show students slides of the beam, or girder
bridge. This bridge can be as basic as a log across a creek.
Its simple design makes this type of bridge easy to build and relatively
inexpensive. Ask students to build their own beam bridges, using
the blocks, candy and strips of poster board provided. Let them
experiment with how many candies each bridge will hold, depending
on where the supports are placed. This activity will help them to
understand that the longer the span, the weaker the bridge, and
if the span is too great, the bridge will collapse of its own weight.
5. Next show students slides of arch bridges.
Explain that the arch is one of the earliest architectural
elements developed, and was used extensively by the Romans in their
buildings, bridges and aqueducts. Ask a couple of volunteers to
demonstrate the arch bridge by pressing their palms together high
over their heads and leaning forward. Ask students where the strength
of this bridge lies. Ask what would happen if the volunteers were
standing on a slippery floor. Then ask how could they counteract
that movement in their bridge design. Lead students to understand
that it’s the strength of the abutments that determine the
strength of the bridge.
Day Two:
1. On the second day, put the students in groups
of five, and give each group about 50 plastic straws, 50
pins and a small plastic container, and ask them to create a structure
that can suspend the container 30 cm high. Give them about 15 minutes.
Then, have them test their structures by carefully filling up the
containers with candy until they collapse. Ask students to keep
track of how many candies their structures were able to hold. When
all groups are finished, come together as a group and discuss students’
findings.
2. Ask students to build two each of three different
shapes: triangles, squares, and circles. Have them experiment
with these shapes by placing the containers on top and filling them
with candy. The weight of the candy will test the strength of each
shape. Again, come together and discuss students’ findings.
These experiments are designed to show the structural superiority
of the triangle.
3. Show students slides
of geodesic domes as well as truss bridges. Ask them why
the domes don’t need interior walls. Then ask them why truss
bridges are most commonly used for trains and drawbridges. Ask them
what the drawbacks might be of using truss bridges. They should
comment on the bridge’s strength because of its shape, but
also note that they are expensive to build, heavy and not that aesthetically
pleasing to the eye.
4. Finally, show the students slides of suspension
bridges. Point out the cables, and explain how the suspension
bridge works. Ask students what the advantages and disadvantages
of suspension bridges are. They should note the beauty of the bridge
and its ability to span long distances, but also see the complexity
of the design, and the expense of the materials used.
5. After students have mastered bridge vocabulary
and concepts, assign them the task of building their own
bridge. They will become the bridge engineers, and apply their own
expertise to solve a real transportation problem. Ask them to use
their imaginations to create a geographical situation that requires
building a bridge. They should choose the bridge that would work
best in the situation they create, while taking into account the
location, the strength required and aesthetic considerations. They
will then build the bridge using materials of their choice.
6. When the bridges are completed, ask
students to bring them to school and present them to the class.
They should explain the transportation problem, the solution, and
why this particular bridge type was chosen. They can discuss the
advantages and disadvantages of their bridge, and describe its attributes,
including strength and aesthetic appeal. Ask students to use as
much bridge building terminology as possible in their presentations.
Related links on this site:
Evaluation
Before students begin working on their bridges, bring them together
in a large group and ask them to help create a grading rubric. Ask
them what attributes a topquality bridge project might have, and
list those attributes on an overhead projector or white board.
Possibilities might include:
 Bridge is well designed and crafted;
 Type of bridge chosen matches the transportation problem described;
 Arguments for building a particular bridge are well supported;
 Bridgebuilding terminology in used in the presentation;
 Shows adequate investment of time and effort
Evaluate each attribute on an appropriate scale based on your own
school’s grading system, for example giving points or letter grades.
Include student evaluations also, if desired.
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