I did this with my students today. I saved up a bunch of water bottles and the students watched as I put it together. All you do is add some water, oil and food coloring. I put a little super glue on the lids so my behavior babies wouldn't have the chance to make a mess.
I teach kindergarten, so I used the younger version of the papers I created. I first let them explore with the bottles, tilt them, move them, give them a little shake. Then I had them get our their science journals. We added this paper. I gave them a minute to draw a picture of their bottle. Then we talked about what we saw. After a little discussion, I then asked them why they think this happened. I got some awesome results like: "maybe the oil is heavy and pushing all the color down, because the color always stayed on the bottom." The students were really thinking.
I also included a little bit older friendly version that asks the students to make predictions. Was their prediction correct. Explain.
I love science journals and experiments. The students have so much fun! I hope your students enjoy it as well!