Hydrophobic experiment, take 2

Our last hydrophobic experiment was less than successful, although we did learn that you can't dye olive oil with food coloring. Part of the problem was one of scale - it was too difficult to see the color difference with just a small layer of oil. This time we filled a small water bottle half full with water dyed red with food coloring. We then filled the other half with olive oil and sealed the bottle. We then shook up the bottle, making the liquid one uniform color. Nearly instantly the oil, being hydrophobic, started to separate out. We checked on the bottle every 1-2 minutes, watching the water and oil slowly separate. Within about 10 minutes, the two were almost completely separated, with a yellow liquid (oil) section and a red liquid (water) section.

What I liked about this experiment:

It allows a lot of jr. scientist participating - after the raw materials are in the bottle and the bottle is sealed, they can do the rest of the experiment themselves

It's infinitely resettable - at any point the bottle can be shaken and the experiment restarted

It's robust

It works quickly

It's fun

Tin can phones

We had some empty giant coffee creamer plastic containers so we decided to make some "tin can" phones. We had made some before using paper plates, string, and popsicle sticks (wrapping the string around a popsicle stick up against the plate), with limited success. The coffee creamer containers worked much better, probably because they captured sound better and added their own funny-sounding resonance. We also figured out that we could use one of the containers as an amplifier so when we strummed the string between the two "phones" we could hear a clear note come out of each container - a good example of how the string was transporting vibration and the containers were turning those vibrations into sound (o.k., technically the ear was turning them into sound and the containers were just amplifying and modifying the vibrations). Overall I'd say it was a fun experiment that worked well.

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.

Sun-bleaching

We're starting to do some experiments using the sun. The big downside is that these tend to take awhile so they're more set-it-and-forget-it types of experiments. Our first sun experiment is sun-bleaching. Since the sun will bleach color out of construction paper (or just about anything else), we set up a sheet of bright red construction paper in a window that gets strong sunlight and put a few objects on it - the idea being that the sun will bleach all of the paper except what is under the objects and we'll end up with permanent "shadows" of the objects.

Our first attempt was thwarted by our cats, who clearly aren't big fans of science (they often try to chew on the materials for our science projects) who knocked all the objects into different places on the paper each day, giving us multiple and ill-defined "shadows." Still very exciting to see that the experiment can work! We're now clipping a key to the paper, which I hope will prevent the cats from causing more mischief.

Next up: sun dials and pin hole (construction paper) cameras.

Invisible forces

Materials
clear tupperware
pen
string
paper clip
magnet

Results
Success

Working theory
Since magnetic fields can't be seen, if we tether a paper clip and put something between the paper clip and the magnet, the magnetic field should be more apparent.

Experiment
We tied a paper clip on a string and tied the other end to the middle of a pen. We put the pen across the top of a clear tupperware with the paper clip just touching the bottom of the tupperware. We moved a magnet around under the tupperware, dragging the paper clip around through the tupperware without it getting "stuck" to the magnet.

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.

Paper clip trains

Materials
paper clips
refrigerator magnet

Results
Success

Working theory
Ferromagnetic items (generally those with iron) can be magnetized. By rubbing a magnet across a ferromagnetic item like a paper clip, you can temporarily magnetize the item.

Experiment
We repeatedly rubbed a refrigerator magnet along a paper clip (always in the same direction - not sure if that matters). We were then able to use the magnetized paper clip to pick up another paper clip. By rubbing the magnet along multiple paper clips, we were able to make a series of magnetized paper clips. Placing them head to tail in a line we were then able to pull the whole train of paper clips by pulling the first one. We also magnetized other objects like certain keys, finding out that we could only magnetize objects that the refrigerator magnet would stick to (i.e. those that are ferromagnetic).

Rubber band guitar

Materials
Kleenex box
rubber bands
pens

Results
Success

Working theory

Sound results from periodic (i.e. regular) vibrations. Changing the length, thickness, or tautness of a rubber band should change how it vibrates and what pitch it produces.

Experiment

We started by placing different sized rubber bands around an empty Kleenex box, strumming the part of the rubber band that was over the opening of the box (where the Kleenex come out). This created a muted and muddy sound. Thinking the rubber band was up against too much of the box, preventing sustained vibrations, we moved two pens under the rubber bands and strummed in between them, making a nice note. By changing the distance between the pens (lengthening or shortening the part of the rubber band that vibrated), we were able to systematically change the pitch we got.