Building Bridges
Presented by l'Acad�micien
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1. TITLE: Straw Bridges
PURPOSE:
To build a bridge made out of plastic straws and scotch tape that will support the most mass.
OBJECTIVES:
The student will:
1. Construct a model of a bridge, which will support as much mass as possible.
2. Understand the value of triangles in physical structures.
MATERIALS: (per team)
1. 30 plastic straws
2. I roll of scotch tape
3. 1 pair of scissors
4. Ruler
5. Wooden support structure
6. 1-8oz paper cup:
7. Several pennies
8. Balance
SKETCH:
PROCEDURE:
1. The students will work in teams of two.
2. Each team will be given the listed materials.
3. Each team will count their straws to be sure that they have 30 straws.
4. The students will be given 30 minutes to construct a bridge using only the provided materials.
5. A place for the cup to sit must be built into the bridge.
6. The cup may NOT be taped to any part of the bridge.
7. At the end of 30 minutes, the students will be instructed to stop and no more construction will be allowed.
8. While the teacher, or appointed judge, is watching, the student will add pennies to the paper cup until the bridge sags enough so that any part of the bridge touches any part of the bottom support structure.
9. The cup and the pennies are placed on the balance and the total mass of the cup and pennies is recorded.
10. The bridge may NOT be wrapped with tape.
11. The cup must sit in the center of the bridge.
12. The students may (should) use plans or drawings to help in the construction of the bridge.
Scoring:
1. Each team scores 10 points for each UNUSED straw, plus 1 point for each gram the bridge supports. (The last penny added DOES count)
2. In the event of a tie for first place (only).
a. The team having the most UNUSED straws will win.
b. if the tie still exists the bridges will be re-positioned on the support
structure and pennies will be added again as described in the rules above.
c. if the tie still exists, duplicate 1st place awards will be given.
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2. TITLE: Bridge Building Contest
Purpose:
To build a bridge, constructed from toothpicks, that will support the most weight as compared to its mass and length.
Objectives:
The students will:
1. Use their knowledge of geometry in designing a strong structure.
2. Apply their knowledge of forces and vectors in the construction a model.
3. Test their model under laboratory conditions.
Materials:
1. Flat toothpicks "Richwood" Birch (flat).
2. White glue (Elmer's).
3. Balance.
4. Meter stick
5. Scale
6. Bar, Hook, Sand and Bucket
Sizes: Length - Mm. 18 in., max. 22 in.
Width - Mm. 3 in., max. 7 in.
Height - Mm. 1 toothpick higher than the place where the load plate will be placed. (sub structures are legal).
Testing
You must make a place for the bridge to be loaded. The teacher will have the bar and hook. You must make a place in the center of your bridge where the bar and hook can be placed. (See sketch)
Scoring
150 points for any bridge that meets size requirements and will support at least 4 pounds.
Y= load (how many pounds holds) x length of bridge (inches)
mass of bridge (pounds)
SKETCH:
TEACHER NOTES:
- This activity works well for 8th grade students and above. It is not recommended for younger students because of the lack of small motor coordination skills in most younger children. There is a 1'frustration factor" because the toothpicks tend to move easily when they are being glued and tend to stick to the students fingers.
2. The bridges do not necessarily need to be able to have a small car drive over them. Most bridges are more of a structure that spans a distance and many will not look like real bridges.
3. A discussion of construction techniques is helpful before the students begin to build so that they begin to realize how real bridges are constructed. Be sure to point out the existence of triangles in most bridges.
4. Students should be encouraged to draw a full scale drawing of the bridge before they start construction. They can pin the drawing to a large flat piece of wood and build directly on it.
5. One of the main problems with most bridges is that they are not symmetrical. A bridge that is not symmetrical will tend to twist rather than break. The teacher should emphasize the importance of side to side support as well as vertical support.
6. One of the most important factors is that the glue must have time to dry. Many times the best designed bridges fail because the glue is still wet. Students should be encouraged to let the glue dry for 48 hours before testing. (You may make them due on Friday and test them on Monday!)
7. Well made toothpick bridges will hold several pounds. It is not uncommon to see a bridge hold over 100 pounds. The best bridge ever recorded was 22 inches long, had a mass of 126 grams, and held 242 pounds!!
8. The support bar should be made from heavy metal or HARD WOOD (oak or walnut should work). The students should be able to see the bar and hook before they start to build because they need to make room in the bridge for the bar and hook.
9. Two tables set from 18 to 22 inches apart with the 2 x 4 supports fastened to them with a "C" clamps work well as a test bed. The bar and hook are inserted in the bridge, the bucket is attached, and sand is added to the bucket. When the bridge fails the whole set up (bar, hook, bucket, and sand) are weighted. This will give the value for the "Load".
Hint: Use the scale from the gym or clinic to weigh the load. (Customary measurement units are used in this activity because many students have problems in obtaining metric measurement devices.)
10. The bridges should be measured and weighed before they
are tested this data should be recorded on the data table.
(see below) You will need some kind of a lab balance to
get the mass of the bridges. Most bridges will have a
mass from 100 grams to 400 grams. (Use 1000 grams =
2.2 pounds to convert grams to pounds)
Name |
Lenghth (inches) |
Mass of Bridge (Pounds) |
Load (pounds) |
Score |
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Lesson plans from Mr. Ross Smith, James Morden Public School, Ontario, Canada.