Bridges: Teacher Notes
Engineers test the materials
used in construction of buildings, roads, bridges, etc., for durability,
strength, and safety. Testing models gives them the information in
a manageable, cost efficient manner. The following activity is similar
to a procedure used in testing the strength of bridge beams.
Students work in pairs.
Each pair needs:
- 1 paper cup with 2 holes
punched on opposite sides
- 1 cupful of pennies
- Uncooked spaghetti (about
- Thread a piece of spaghetti through the holes in the cup.
- One person will suspend the cup by placing each index finger approximately
one inch in from the ends of the spaghetti.
- Another student will carefully add pennies to the cup, one at a
time, until the spaghetti breaks.
- Record results below.
- Repeat the above procedure with 2, 3, 4, and 5 pieces of spaghetti
until one or more pieces of spaghetti breaks.
# of spaghetti
# of pennies
- GRAPH THE RESULTS: Plot the data from your table on a coordinate
plane as ordered pairs (x, y).
- READ THE RESULTS: Looking at your graphed points, do they
seem to lie along a straight line or curve?
Use the graph to answer the following:
- Find the number of pennies needed to break "bridges"
of 6 pieces: _____ pennies, 7 pieces: ______ pennies, 8 pieces:
- About how many more pennies are required to break a "bridge"
each time another piece of spaghetti was added? How can you tell
this from your graph?
- Extend the line or curve you have drawn so that it crosses the
y-axis. Identify the ordered pair where this occurs: (0, ___ ).
It sounds crazy, but the graph may suggest that a bridge of no
spaghetti would crumple with a weight of ______ pennies.
- Describe in words how to determine the number of pennies
needed to break a bridge if you know the number of pieces of spaghetti.
- Use your description to predict how many pennies would be needed
before a bridge of 20 pieces of spaghetti would break. Show your work!
- Translate your words above to an equation that could be used to
determine the number of pennies (y) needed if you know the
number of pieces of spaghetti (x).
- Use your equation to predict the number of pennies needed
to break a bridge of 50 pieces of spaghetti.
As a result of this activity,
students will be able to collect, graph and interpret data.
Have students write answers
to the following questions in their journals:
- Explain how they knew
the graph was linear.
- Using the equation,
find the number of pennies needed to break a bridge of 75 pieces