Bridge Building Series - Truss Bridge 2

Truss Bridge 2 – Straws & tape (A challenge project)

This project needs more accurate taping, which might be a tad difficult for primary students. However, I've done this project with a group of 3rd graders, and they were able to build sufficient truss bridges.

Supplies:

·         A bag/box of straws

·         Tape

·         Scissors

·         Small cups

·         Paper clips

·         Weights – pennies, paper clips, etc. Anything is OK as long as they weigh the same. You want to compare how much different bridge designs can support

    

Instructions:

1.      Cut a bundle of straws to same size (~2 1/2 inches long). Leave some for different lengths. These will be cut to size.

2.      Tape four pieces together to make a square. Tape uniformly across all places. Create enough square to span an opening that is 10 inches wide.

Created bottom of the truss bridge first, then continued to build the sides of the bridge. (These squares measure to 11 inches in length.)

3.      After creating several squares, put cross bracings diagonally (cut these to size).

4.      Put the top pieces last and enclose the truss bridge.

5.      Place the truss bridge between two desks, tables, chairs, etc.

6.      Hang a small cup in the middle of the bridge (use hole puncher and paper clips) and load it with pennies, paper clips, etc. to weigh it down and test its strength.

Same amount as beam bridge

Added more coins

Added another bucket full of coins.

7.      Different size straws, too much tape on one side vs. the other side, etc. will create imbalance and weaknesses in the bridge structure. Try to balance taping, straw usage, etc. on all sides.

This straw and tape truss bridge was much stronger than I expected. I think I could have added another bucket of coins, but I ran out of bridge space. Maybe you can build a longer bridge and test how many buckets of coins your bridge will hold. Of course, the longer the bridge span, weaker the bridge. So, you might have to consider the bridge span vs. support strength of the abutment.

Remember, Engineering is all about failing and trying, again. So, try and try, again.

Bridge Building Series - Truss Bridge 1

Truss bridge building instructions 1

We’ll make different truss bridges using two different materials - foam cubes and cut drinking straw pieces.

Design Rules for both bridges:

1.      Bridge must span 10 inches (25 cm)

2.      Bridge must have a place to attach a small cup in the center of the span (preferred).

3.      The ends of the bridge are not taped onto the support structure.

Bridge 1 – Marshmallow/foam cubes/cheese balls & toothpicks

NOTE: The best material for this project is foam cubes. However, a container of foam cubes can get very expensive (I've paid $27.49 for a container of 105 foam cubes), so if you can find more affordable ones, please let me know.

I've done this project with marshmallows, and it's doable (for intermediate grades). And cheese balls get messy, but doable as well.

Supplies:

·         A bag of marshmallows, foam cubes, or cheese balls

·         A box of toothpicks

·         Tape

·         Small cups

·         Paper clips

·         Weights – pennies, paper clips, etc. Anything is OK as long as they weigh the same. You want to compare how much different bridge designs can support

    

Instructions:

1.   Create a square with four foam cube pieces and toothpicks. Create 3 more. Put them together to create a cube. 

2.   Create several more cubes and put them together until you reach 10 inches in length. Remember, your bridge must be longer than the span it needs to bridge (add an inch or two to the total length of your bridge).

  

3.   Place the bridge between two desks, tables, chairs, etc.

4.   Hang a small cup in the middle of the bridge (use hole puncher and paper clips) and load it with pennies, paper clips, etc. to weigh it down and test its strength.

~same number of coins in the cup as the beam bridge project

added another cup of coins

added more coins to each cup

Again, this project works best with these foam cubes. I purchased from Amazon, but they are pricey. I did find some smaller foam cubes from the Dollar Tree store, and they worked well. But it's very difficult to find them consistently. You can see them on their online store, and the store managers don't seem to know when or if they'll ever get another shipment. So, if you find another source of reasonably priced foam cubes, please let me know.

Strength of Materials - April 15, 2015

These are the pictures from the project I did in the fall. Again, because I had to load the books carefully, and the structures did collapse, I don't have "action" pictures. But these are some of the examples of the support structure the students from 2nd - 5th grades built.

Previous Supplies List:
25 straws (Dollar Store variety)
6 bamboo chopsticks (3 pairs)
scotch tape

New Supplies List:
25 straws (Dollar Store variety)
6 chopsticks (3 pairs)
scotch tape

I couldn't get my hands on the same, stronger bamboo chopsticks, so I had to settle for either thinner, weaker bamboo chopsticks or regular wooden ones. I bought both types, but they didn't quite hold up. Still, it doesn't make this project any less fun to do.

Project Instructions:

1. Hand out 25 straws and 6 chopsticks to each team of students.
2. Talk about load distribution.
3. Build and test.
4. Get more material (another pair of chopsticks or 5 straws) and make repairs. And test again.

The records to beat for next year:
2nd graders - 18 lbs.
3rd graders - 32 lbs.
4th graders - 36 lbs.
5th graders - 46 lbs.

Some load pictures:

Some very interesting designs:

 I have many pictures, but I couldn't post all of them. These are some contenders and some interesting ones.

Have fun.

Fantastic Foam Bridges - March 30, 2015

I do a lot of hands-on building projects because the students seem to enjoy them the most. This project is a variation on a marshmallow bridge project. This one is really exciting for the students because there's an element of competition, which brings and urgency into the situation.

 Supplies List:

•     Foam cubes - it doesn't matter what the size is unless it's really small. 1 inch foam cubes work pretty well.
•     Toothpicks
•     Small cups to hold pennies (tiny cups you'd get from a dentist's office)
•     Paper clips
•     Pennies (up to 700 pennies)
•     Plastic tub (to catch the pennies if/when the bridge collapses)

I draw a couple of truss bridge designs on a white board and talk about the triangles in the bridge design. Then I go on to talk about the advantages of using triangle; however, I caution them about the hypotenuse. With the toothpicks, the students have to do something about the length difference.

Project Instructions:

1.     Hand out a tube of foam cubes and ~250 toothpicks to each team of students.
2.     Build whatever shape the team wants to build.
3.     Build, test, & build, again!

Here are some records to break for next year:
 
2nd graders - last year, 298 pennies
3rd graders - this year, 250 pennies
4th graders - this year, 450 pennies
5th graders - this year, 650 pennies

I don't have a lot of class pictures because I have to load the pennies very carefully, evening out the load on the bridge. So, the teachers take the pictures, but I haven't received the pictures, yet. So, here's what I have.

~150 pennies in the right and the left cups each

Try this one at home and have a wonderful time.

P.S. - The only problem with this project is that the foam cubes are quite expensive (between $17.95 - $24.95 per 102 cubes), and we can't keep reusing the foam cubes. So, it does get expensive for a class project when I try to collect $10/year/student for the science projects. If you know where I can get them cheaper, please let me know.

Absolutely Amazing!

I started volunteering in classrooms in 2007, and since then, I've conducted over 350 - 400 science projects in classrooms. I usually have projects I do each month, and I follow that because it gets too confusing to schedule different projects in 9 - 12 classrooms a month. Well, this month, it was our last project of the year in one of my second grade classes, and the teacher and I couldn't really think of a special project (after all these years, I struggle to make these projects fresh and interesting to children who were already exposed to them in the previous year and to myself as well). So, I just gathered up the supplies I had left over, and headed for the classroom. This was going to be a very open-ended project (the kind I like best).

This is what I gave to a class of 2nd graders (four groups of six students but smaller the better).

Supplies List:
25 straws (Dollar Store variety)
6 bamboo chopsticks (3 pairs)
scotch tape

I told the students to make a tower of some kind that would hold up at least one of their hard cover, heavy textbooks. I had 1 1/2 hours, and I gave them first hour to come up with a design and build their first version. After the first hour, this group built a structure that held almost 2 textbooks when all the other groups failed.

After the first design and build attempt, I gave additional five straws and another pair of chopsticks to all the groups with some ideas to make their structures stronger.

Well, this is the result and it blew me away. I thought maybe, just maybe a 2nd grader group could build something that would support 3 - 4 textbooks, but a group of them built something that held up 9 textbooks. That's probably between 20 - 25 pounds or more (I tend to underestimate weight consistently). What an awesome achievement! Another lesson in underestimating our children.

I actually think this structure could have held at least one more book, but we didn't have it handy. A little boy ran to the shelf to get another book when it collapsed. Amazing!

Without the books on top.

This turned out to be one of the best projects! I'm definitely going to use this project next year.

Try it at home and have fun.