Hypothesis testing

Jr. scientist A came up with a hypothesis and we decided to test it. He had discovered that the pump for his stomp rocket had a little nozzle that could be removed. He hypothesized that the nozzle, with its smaller opening, would result in less air being pushed out of the pump and thus the rocket would fly a shorter distance (personally I thought the smaller nozzle would result in greater pressure and thus a longer distance flight). We tested the hypothesis by setting up the stomp rocket and firing off rockets either with or without the nozzle in place. We marked each place the rocket landed - blue for with the nozzle and white for without. To my surprise, all three white lines (no nozzle) were farther than all three blue lines (with nozzle). This was a moderately well received introduction to rigorous hypothesis testing, but clearly a tad bit advanced for Jr. scientist A.

Baking soda and vinegar reaction without the vinegar

We found this reaction by accident. We decided to try to make baking soda crystals. Just like we've done when making salt crystals, we started with dangerously hot water so that we could dissolve a lot of baking soda into the water. To our surprise, when we dropped the first spoonful of baking soda into the water, it fizzed up as if there was vinegar in the solution. Thinking that I had grabbed a container that had a little vinegar residue in it, we marched on with our crystal experiment (standing a little farther back). Every time we added baking soda, we got another fizzy reaction, long past the point where any vinegar residue would have been used up in the reaction. It turns out that mixing baking soda into hot water does create carbon dioxide, just like when mixing vinegar and baking soda. Granted this was (unintentionally) not the safest experiment, but it's always fun to find a new fizzy reaction. Of course, Jr. scientist A had quite a lot of fun repeating this one.