Rocket balloon

This should work. Inflate a balloon, attach it to a straw with a tethered string running through it, and when you let the air go out of the balloon, the "rocket" should be propelled along the string. But despite various different rocket "designs," we haven't been able to get this to work. We've tried taping a big balloon directly to the straw with packing tape (the balloon may move a little along the rope but not very far - and re-inflating the balloon tends to make it pop because of the tape stuck to it), attaching a paper towel tube to the straw and sticking a long thin balloon into it (the rocket doesn't move at all), and taping a long skinny balloon to the bottom of the paper towel tube (again, basically no movement). Maybe it's not enough force, maybe the pressure is not being well directed. All I know is we can't seem to get this experiment to work. How frustrating!

Hydrophobic experiment

Trying to demonstrate what it means for something to be hydrophobic, we mixed together water and oil in a small (2 Tbs) measuring cup. The result was a rather unimpressive separated mixture with one layer clear and the other label an unimpressively different slight yellow. We added some red food color to the mixture - still not an impressive difference between the two layers. We tried to dye the oil a different color and learned that whatever the food coloring is made of, it's either water of hydrophilic - at best, we could get little dots of color in the oil. We'll have to work on this one.

Baking soda and vinegar rocket

Materials
soda bottle
scissors
baking soda
vinegar

Results
Perplexing

Working theory
Combining baking soda and vinegar creates a large amount of carbon dioxide gas, causing the mixture to expand and bubble out of the container. If we can direct that pressure downward, we should be able to propel the container upwards.

Experiment
We took an empty soda bottle and used a scissors to poke a hole in the lid. We put a good amount of vinegar into the bottle and filled the cap with baking soda. After our safety goggles were on we put the cap on the bottle and shook it up (with a finger over the hole). We placed the bottle on the ground, cap side down and stood back. Although the bottle became very pressurized and a bubbly stream came shooting out of the hole, we didn't get any lift. We think that either pressure was going out of the edge of the cap, near the threads (aimed upwards) or the cap wasn't flush against the ground, causing the pressure to go out at an angle.