Archimedes screw pump
I suggested about a dozen different projects to our third grader before we found the one she wanted to do---she wanted to build an Archimedes screw pump. Archimedes originally designed this pump to remove water from a leaking ship. The design is still used in many modern day pumps. The version we built involved wrapping a vinyl tube in the form of a helix around a PVC pipe. As you rotate the PVC pipe, the lower end of the vinyl tube scoops up water. As the pipe continues to rotate, the water moves up toward the upper end by moving down inside the helical tube. It's quite a remarkable invention by Archimedes. Here's a video of our version in action:
Extracting strawberry DNA
Our fifth grader wanted to do a project with DNA. We found a simple project to extract strawberry DNA. You start by smashing some strawberries to pulp and adding a concentrated detergent solution. The detergent pops open the strawberry cells (the technical term for this is lyse), releasing strawberry DNA into the solution. You then separate the solution from the strawberry pulp using cheesecloth, and pour the solution into a test tube (instead of a test tube we used an inexpensive rain gauge that we found at the local hardware store). Finally, you pour chilled rubbing alcohol into the test tube. The alcohol forms a layer above the strawberry solution, and remarkably the DNA precipitates out into the alcohol! Here's a picture of the DNA we extracted:
The white stringy stuff is the DNA that has precipitated into the alcohol. (We didn't have any way to verify that this was indeed DNA---we're just assuming that it must be DNA!)
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