Experimentation is at the heart of modern science education. Many non-scientist consider experimentation to be the only true aspect of science. In fact, this is only one part of science. However, it is the part that is most frequently tested at the secondary school level.
As such, this curriculum unit has students performing experiments. They are not, however, traditional hypothesis driven experiments. These experiments are designed to produce observations which will be used in the later construction of the gingerbread house. These experiments will test the strengths of the materials the students propose to use in their houses under conditions which will simulate those that the materials will suffer in the actual building. Aside from being good science, these experiments save time and a good bit of heartache during the final construction phase of the building.
Begin Researching Gingerbread House Materials
Gingerbread houses are traditionally built of gingerbread. However, there are a number of modern substitutes for the gingerbread, and there are, of course, all of the decorations to consider. Because it is important for the students to learn how to do basic research, the students will do some research into the various materials that are used to make gingerbread houses. This research will also help guide the students in their later design efforts as it will help them to establish parameters for size and other design features.
Most of this research will be conducted online; however, the books listed in the gingerbread section of the resources are also good resources for this section of the unit. There are many excellent websites exclusively dedicated to gingerbread houses. Additionally, there are many more sites dedicated to recipes and cooking. Furthermore, many children's craft sites also have sections on gingerbread houses. Some sites even allow the user to plan decorations for their houses online. In my class, a number of these online sites will be collected together on a webpage which the students will use as a webquest in this particular activity. There are a number of free web hosting sites that are easy to use and could be used in other classrooms. Incidentally, this is another way to introduce technology into the classroom. It could even be a project that some students could do on their own.
From this activity the students will exit with a list of potential gingerbread house materials. It will probably include gingerbread, graham crackers, wafer cookies, icing, and various candies. These materials will then be used in the materials strength testing.
The Stonehenge Experiment
All buildings are made up of different elements. Most doorways, for example, are made of two posts and a lintel. Many porches consist of columns supporting a roof. Understanding basic building elements like these will help students to understand the slightly more complex materials strength testing that will follow. Most of these basic elements may be made from a simple set of children's wooden blocks. In fact, some, like the arch, are traditionally included in the set. These blocks are very useful in showing how a building is made up of various elements. Furthermore, if these blocks are combined with uniform slabs of playdoh, it is easy to demonstrate were the weight from applied loads ends up in various different structures.
In this experiment, or demonstration, tell the students that they are building a circle of standing stones like Stonehenge. These stones must also support stone lintels over the stone posts. All of this stone is going to produce a huge weight, officially called a "load". The students have to figure out the path that the load is going to travel from the lintels into the ground so that standing stones, aka posts, will be placed to provide enough support to carry the load. Feel free to make up your own back story here, if you don't like mine. In this experiment a fairly thick slab of playdoh, about a quarter of an inch thick, is placed between pieces of the structure. The slabs of playdoh will be indented at the places where a force is being exerted when a load is applied to the structure. Good spots for the playdoh slabs include the bottom side of the lintel, on the table under the posts, and anyplace else that two pieces of the structure come into contact. Once the posts and lintel are set up, you add weight to the lintel until you start to get impressions in the playdoh. The experiment is a bit more interesting if your posts are not perfectly vertical, but instead are slightly tilted.
A similar experiment can be done for almost any type of basic building element. The most important things to remember about this experiment are: get blocks that playdoh will peel off, and make the slabs of playdoh a uniform thickness.
Materials Strength Testing
Materials exhibit strength in many different ways. The two most common ways, though, are stress and strain. Stress is the amount of load, or weight or force, that is born over a certain area of material. It has the same units as a measure of pressure. For example, a car tire might be under a stress of 33 pounds per square inch. Strain is the measurement of how much a material stretches. It is the increase or decrease in length divided by the original length. In other words, it is the percent increase in the size of a material. For example, when the car tire is inflated to 33 psi, it may expand from its original size. Precisely how much it expands is a measure of strain. J. E. Gordon has a very good explanation of these concepts in his book Structures: or why things don't fall down.
In the context of gingerbread houses, stress makes gingerbread walls crumble and bow outward causing strain at the joints of the house. So, the experimentation that must be done on the gingerbread materials must focus on these two issues. This is also a very good place to introduce some of the engineering terms like tension and compression.
One of the easiest ways to study the effects of stress and strain on gingerbread house materials is to use a setup similar to the Stonehenge experiment. In this experiment, two upright pieces of some material like wood support a span of gingerbread material. Small weights are then added to the center of this span. As the weights are added, the material should begin to bend. In fact, it is stretching. The amount of stretch should be measured after each addition of weight. Furthermore, any thinning of the material should also be measured. The division of the weight, which is actually force, by the cross sectional area of the material under the weight will yield the stress on the material. This stress will change as more weight is added because both the load and the cross section will change. The division of the change in length of the material by the original length will yield the strain on the material. Gingerbread tends not to be very elastic, so very small weights should be used.
Another way to measure stress and strain is to suspend a piece of material from a spring scale. As weight is added to the bottom of the material, the material will stretch and eventually break. The same data that was collected in the last experiment may also be collected in this one. The choice depends on the materials available to the particular class.
Experimental Vocabulary
Vocabulary is essential for sensible conversation. Engineering terms in some ways are actually more important than many other forms of scientific vocabulary. The reason for this is that many of the term used in structural engineering are also used differently in common parlance. Therefore, it is essential to student comprehension of their experimental results that they understand the engineering version of the terms that they will be using. This vocabulary list, unlike the architectural one, will be more language based, but it will probably still also have room for sketches. Like the architectural terms, the structural engineering terms also have a strong visual and spatial element to them. Unlike architectural terms, engineering terms often have a very specific meaning which can easily be put into words. So, in this case, the vocabulary list is likely to be a combination of words and some pictures. As with the architectural list, a list of suggested words may be found in the appendix.