|
|
|
Researched by Timothy S. 2000-01 |
|
The purpose of this experiment was to determine which bridge structure would hold the most mass.
I became interested in this idea when I saw a picture of a few different types of bridges. I have also been fascinated by the size of bridges and wondered how they could hold so much weight.
The information gained from this experiment could be used by engineers
to know which type of bridge to build according to the amount of traffic
in that area.
My first hypothesis was that the suspension bridge would hold the most mass. My second hypothesis was that the beam bridge would hold the least mass before failing.
I based my first hypothesis on the article "Bridges," in The World Book Encyclopedia, which states that the suspension bridge's cables are very big and strong. I based my second hypothesis also on the article "Bridges," in The World Book Encyclopedia, which tells that the weakest and simplest bridge is the beam bridge.
The constants in this study were:
- The height of the platform
- Materials used to build the bridges
- The materials used in the testing
- Distance between the piers
- Placing the bridge on the same base
- The width of the bridges
The manipulated variable was the type of bridge.
The responding variable was the mass supported by the bridge before failing.
To measure the responding variable I measured the mass in grams of the sand and the bucket at the point of bridge failure.
| QUANTITY |
ITEM DESCRIPTION |
| 6 |
strips of 4 mm, and 3 cm width, 30 cm long, balsa wood |
| 1 | big bag of sand |
| 1 | bucket |
| 1 | roll of string |
| N/A | staples 1-2 cm across the top |
| 30 | strips of 10 cm high, 3 cm width balsa wood |
| 2 |
strips of 40 cm long, 4 mm width balsa wood |
| 1 | bottle of school glue |
Constructing the Bridges
1. Gather materials.
2. Place the 30 cm long balsa wood on top of the 10 cm high wood. The 10 cm wood should be at the very edge of the long wood.
3. Glue the wood together. You now have a beam bridge.
4. Label these bridges "beam bridge."
5. Build another beam bridge except: on top, 6 cm in from piers, place another 10 cm piece of wood.
6. Cut a 58 cm long piece of string. Staple one side of the string to one of the top balsa wood . Do the same thing with the other end of the string. The 50 cm string should be1/2 a cm in from the edge of the tower. Do the same thing on the other side. The sting should come down diagonally to the edge of the platform.
7. Customize some strings so that they can tie to the top string and be stapled to the platform of the long wood. There should be 6 strings on each side each evenly spaced. On the sting coming down to the edge of the platform, there should be a string tied to it in the very center. You now have a suspension bridge.
8. Repeat steps 6-8 until you have three suspension bridges.
9. Label these three bridges "suspension bridge."
10. Repeat steps 1-2, using a 40 cm long piece of balsa wood instead of 30 cm wood. The pier should be 5 cm in from the edge. Repeat this step 3 times.
11. Put the towers 8 cm from the edge of the platform.
12. Customize string so that they are able to come diagonally down from the top balsa wood. The first string should be at the top, the next five cm down from the top. Repeat this step on each side of each tower.
13. Repeat steps 11-13 until you have 3 of this kind of bridge.
14. Label these bridges "cable-stayed."
Testing
15. Put the bridges into three groups. One type of bridge in each group.
16. Attach a bucket to the very center of the first beam bridge.
17. Very slowly and carefully pour sand into the bucket until the bridge fails (cracks or breaks.) If the bucket gets too full, use rocks
18. Weigh the sand and the bucket on the triple beam balance.
19. Record data.
20. Repeat steps 17-20 on the cable stayed bridge.
21. Repeat steps 17-20 on the suspension bridge.
22. Repeat steps 17-21 for trial two.
23. Record data in data chart.
24. Record observations in experiment log.
The original purpose of this experiment was to determine which bridge structure would hold the most mass.
The results of the experiment were that the cable stayed bridge held the most weight, then the suspension bridge and the beam bridge held the least weight. The second beam bridge held 6251.3 grams. That was more than both suspension bridges and the first cable-stayed bridge. When you averaged both beam bridges it was 4372.1 grams. The cable-stayed bridge averaged 5845.6 grams, while the suspension bridges held 4651.8 grams. The first suspension bridge cracked along the staples. I think that when the staples dug into the wood, it weakened the bridge.
My first hypothesis was that the suspension bridge would hold the most mass. My second hypothesis was that the beam bridge would hold the least amount of mass.
The results indicate that this first hypothesis should be rejected. The results also indicate that my second hypothesis should be accepted.
Because of the results of this experiment, I wonder if I built the same structure of bridge with slightly different materials, if they would hold different amounts of weight.
My findings should be useful to engineers, because they will know that the cable-stayed bridge is much stronger than the suspension bridge.
If I were to conduct this project again I would cut my wood more square. I would have three trials instead of only two. This would "break the tie." I would also do something better than staples so that the suspension bridge would be stronger.
- My dad helped me while I was cutting wood for the bridges. When I conducted the experiment, he suggested what to do. He helped me weigh all of the mass that caused bridge failure. It got very complicated, because the mass went over what the balance supplied for us to use. He and my mom were also my biggest supporters. They spent lots of money on balsa wood for me.
- Mr. Newkirk stayed after school so that I could work on my science board and journal.
- Mrs. Pasckvale gave advice on my board in areas I never took notice of. She helped me cut the papers that I put on the display board.
THANK YOU!!!!
Top of page