## Building Tetrahedron Kites

Few things capture the spirit of spring like flying a kite. Watching a kite dance and sail across the sky is not only a visually appealing experience, it also provides a foundation for studies in aerodynamics – a discipline that beautifully integrates science and mathematics.  Building tetrahedron kites combines art and handcrafts as well.

## The Science of Kites

A kite is a tethered aircraft that flies when the forces of lift and thrust are greater than the forces of drag and gravity.  In between flying and crashing to the ground are a variety of swoops, wiggles, pitches, yaws, and rolls that show the kite is seeking a balance among the conflicting forces.

A kite creates a physical obstacle to the normal airflow which causes the air to change direction and speed. The air flows across one surface faster than it moves across the other side of that surface. This difference in speeds results in lift in the direction of the surface with faster moving air. As air pressure can be altered by changing the kite’s angle of attack, the changes in air speed result in changes in air pressure, which cause the kite to produce greater lift.

## Constructing a Kite

Begin by constructing a pyramid composed of equilateral triangles by running string through three straws, arranged in a triangle.  Continue on with the string through two additional straws, forming an additional triangle (the two triangles now share the same base).  Finally, run the string through one more straw and lift the left triangle upward to form a pyramid, tying the the lead end of the strings.

Use the template pictured here to cut out a tissue-paper covering for two sides of the tetrahedron. The template measurements are for standard length drinking straws.  Cover only two sides of the tetrahedron.  Glue the covering over the frame, wrapping the excess materials around the straw frame.  Repeat these steps to create a total of four tetrahedrons.

More detailed instructions for building these kites can be found at Easy Kitemaking: How to Build a Pyramid Kite.

## Designing an Experiment

Now that you have familiarized yourself with the characteristics of the tetrahedron kite, design an experiment to determine how changing one variable in the kite’s design will affect its performance.

For example, you may wish to build a kite using heavier tissue paper or a different kind of covering altogether (newspaper, plastic wrap, or aluminum foil for example).  You may try a kite with a larger number of tetrahedron cells (16 instead of 4).

## Bicycle Breakdown

We had such a good time this week with our science co-op.  For the past few weeks we have been meeting with to take part in an 12-week introductory physics class.  Today was the culminating activity for a unit on simple machines.  The kids had been looking forward to it for weeks and their enthusiasm was evident in how engaged they were throughout the lesson.

For Christmas each of the kiddos received a new bicycle from Santa.  I purposely held onto their old bikes for this activity.  If you would like to do this activity yourselves, I would encourage you to check with local bike retailers for an old bike they may be willing to donate to the cause.

Before we began, we reviewed the names of the 6 simple machines:  lever, wheel & axle, inclined plane, wedge,  and pulley.  We then discussed that a bicycle is a machine made up of many simple machines.  These simple machine work together to make a very efficient machine that helps us move distances much faster than on foot.

The kiddos worked in two small groups of 3 … just the right size to assure everyone had a fair chance to use the tools.   They examined the bike only briefly and immediately went to the pile of tools I had provided (some that were purposely of no use) to begin they process of taking it apart.  Of course, they wanted to work in segregated groups .. the boys took apart Buddy’s old bike while the girls dismantled MeiLi’s.  As they worked, they were encouraged to sketch the simple machines that made up the bike.  They were so engrossed in the activity, however, that this didn’t happen.

Everyone worked really well together and despite the fact that they did NOT record the simple machines they identified on paper, they stayed focused on the activity for nearly 2 hours.  It was such a delight … even us moms had an opportunity to visit … for me, that is a real treat!

At one point, the boys encountered a very troublesome bolt that was too tight for even I to loosen.  Fortunately, DH was home and showed us a little trick.  Using two wrenches, we extended the arm of the lever and thereby were able to loosen the bolt with less force.  Even I learned something today!

## Building Toothpick Bridges .. a Lesson Plan

We have an opportunity this year to participate in our first homeschool science fair.  The kiddos have been fascinated with bridges for a long time so I knew immediately what project we’d undertake … Toothpick Bridges.  I’ll share with you my toothpick bridges lesson plan with you here.

## Capture Their Attention

Before we began construction, we read again the delightful picture book Bridges Are to Cross by Philemon Sturges.  We then used the internet to make observations of many modern bridge designs, particularly those we were familiar with here in Oregon as well as those we’d seen first hand in San Francisco.  I set up a little demonstration to show what structure was strongest … squares or triangles … using just drinking straws taped together at the corners to form a square and a triangle.

## Strength in Design

I then gave the kids graph paper with which I instructed them how to begin designing bridges of their own.  They came up with several designs each – some of which weren’t feasible for toothpicks.  They then selected a design that would most easily be reproduced with toothpicks and we proceeded with construction.

## Building Bridges with Toothpicks and Glue

In the classroom setting, I used to provide each team with a predetermined amount of money with which they would need to purchase their material … lumber (toothpicks) and welding material (school glue).  However, here at home, their imagination and thereby their design were the only limitations.

## Testing Bridge Strength

We tested the strength of the bridges by suspending a gallon-sized milk jug beneath the bridge with a pencil.  Initially, we had used a smaller container but it turned out to be too small to contain the weights.  We then began to slowly add weights (marbles & metal washers) to the container.  When we ran out of weights, I began to slowly pour water into the jug.

We continued in this way until the bridges finally collapsed or gave in to the pressure.  In the classroom, the eminent collapse and destruction of the bridges was always a highlight and was met with cheers and shouts of enthusiasm.  Here at home, I hadn’t anticipated the the big tears that we experienced.

In the end, the two bridge far surpassed our expectations.  Buddy’s design took on 16 pounds before it finally succumbed to the weight.  Sweetie’s design held more than 19 pounds!  Had she had more trusses along the roadway that supported the pencil, we hypothesis that her bridge could have supported more weight as her bridge remained intact with the exception of the road that gave way.

The kiddos are looking forward to presenting their experiment on Friday at the science fair.  Buddy is even talking about building more toothpick bridges – but he says he doesn’t want to test them.  “I don’t want to break my bridge.”

For more details and links to do this project with your kids, check out my Engineering Marvels: Bridges unit study.