The densities of different liquids can be easily demonstrated by making a density column. Steve Spangler has a splendid density column demo that I decided to make on a much larger scale. Instead of using a graduated cylinder I decided to use a fluorescent light bulb tube guard. To seal one end of the tube I used duct tape and Goop so that no liquid would leak out. Once the tube is ready, it's just a a simple matter of pouring the liquids into the tube according to their densities. Check out the video for the results and for some additional tips.
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I picked up this in a toy shop. Students are fascinated by it and always wonder how it works. Once they learn about density, they figure it out pretty easily.
Eggs have an arch design in which compression forces are diverted from the top and bottom of the egg down to the sides. How much compression force can an egg take before it's smashed? Watch the video!
A polymer, sodium alginate, reacts with calcium chloride to produce calcium alginate. Calcium alginate is a gel that is not soluble in water. A new branch of cooking, called molecular gastronomy, uses this technique to trap flavor sauces in gels to put over food. Not familiar with molecular gastronomy? Lifehacker has a good set of simple videos on the subject. You can order the kit that I used from Educational Innovations.