Building a bridge out of Popsicle sticks or toothpicks is a common project for a beginning physics class. The point of this exercise is to demonstrate distribution of force, capacity, resilience, strength and basic principles of engineering. The key to building a really strong Popsicle stick bridge is understanding where the stress or load bearing points of your design is. Once you've identified those areas, it is fairly easy to reinforce the bridge so it is capable of bearing weight up to 50 lbs. and flexing only to the standard of 1.5 centimeters.
Draw the plans for your bridge to scale. Refer to an example of a Warren Truss bridge to help you create your design. On one piece of paper draw the bottom of the bridge. On the other two pieces of paper draw each side of your bridge (left and right). Mark the pieces accordingly so that when you are assembling the bridge later you know which piece goes where.
Lay out the Popsicle sticks on the pieces of paper on top of the scale designs. Glue the pieces together using white glue and allow to dry overnight.
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Assemble the bridge and glue the bottom and side pieces into place. Examine the design and see if once assembled you can identify any weak points in your design. If you can, reinforce them with Popsicle stick subdivisions or more glue. Allow the project to dry overnight.
Build the base using a base diagram. Measure 2.5 centimeters from the left edge and draw a line using your ruler. Measure 2.5 centimeters from the right edge and draw a line using your ruler. This divides your cardboard base into thirds. In the center third, cut a 4-centimeter square hole for the scale string needed to test the bridge. Draw a 5-centimeter square in the center of both the left and right third of the base. This is where your bridge will sit to test the load.