Today we came into the room and saw the tables pulled apart. However, they had a piece of cardboard duct taped to them creating a bridge. Intrigue filled the children as they tried to figure out just what Mr. Jack was up to.
Once the stragglers arrived, Mr. Jack began. He pulled out a box of clear drinking straws and sat them on the first table. The children looked around at each other and waited.
Mr. Jack asked if they thought the straw was strong. There were mixed opinions amongst the group. Where was this leading?
He had one child bend the straw in half. Then he had another child try to pull the straw apart. What conclusions could they draw from these simple experiments?
The straws have weak points and strong points. We can compress the straw in the middle and cause it to bend. We cannot pull the straw apart due to the tensile strength it has. How can we use these properties to build a bridge?
Mr. Jack discussed various bridges the children would be familiar with and the shapes found on the bridges. He brought out a square he made of the straws and let the children determine if the shape was very supportive. He then brought out a triangle he had made of straws and let the children compare it to the square. They determined the triangle was much more supportive.
Mr. Jack told the children about why bridges and buildings must have some 'give' to them. He explained why they shouldn't have a lot of 'give' to them sighting the Tacoma Narrows Bridge aka The Galloping Gertie.
Their task was to build a bridge that would span the gap in the table. The bridge needs to be strong to hold weight without collapsing.
Some children worked in groups, others individually. They were all transfixed on creating the perfect bridge. Masking tape was being ripped. Straws placed strategically and taped together. The span measured. Decks built.
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| The girls are discussing how to build their bridge. |
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| Mr. Jack showing the boys how to build the triangles. |
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| The girls are still discussing the plans. Notice the boys are busy building. |
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| Little Man busy taping his straws. |
An hour passed by so fast that it seemed like mere minutes. Half of the children were done. The other half still working and finalizing their masterpiece.
Time to test the strength of the bridges! Whose bridge would hold up the best?
The children eagerly gave their bridges to Mr. Jack to test. He had a 6 volt lantern battery for the weight. Would the bridges hold up to the weight?
A group of three teenagers went first. Their bridge contained many triangular supports on the sides extending upward. The bridge looked very futuristic and solid. The weight was applied. The bridge held, but it did give in the middle. The teens were satisfied with the results. Mr. Jack critiqued their bridge with pointers on where to add more triangular support.
Little Man was up next. I had helped him a bit with the taping and deck, but he came up with the design. Mr. Jack placed the weight on his bridge. It held all the weight and did not give. Little Man's eyes lit up and he smiled. The teens had been beat by a seven year old. They took it in stride.
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| Little Man watching the weight pull on his bridge. |
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| Mr. Jack explaining why Little Man's bridge held so well. |
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| He is so proud of his bridge! |
Other bridges were tested and had to much give.
Finally, Egee and her group's bridge was tested. It held the weight, but wanted to twist at the top. More support was needed to stop the twisting. The girls were proud of their bridge.
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| The girls turn. |
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| The bridge is starting to twist. Mr. Jack is telling them how to correct the problem. |
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| They still think their bridge is pretty good. |
Another fun day with Mr. Jack!
