In plain water the drop slowly swirls and moves throughout. In salt water, the drop starts to sink and then rises. In the fizz water, the drop quickly disperses and evenly colors the liquid. The gas bubbles in the fizz water act to speed things up, like an invisible stirring spoon. The drop of food coloring is quickly broken up and carried to all parts of the liquid.
Salt water is more dense than plain water.
The juice is used to test the pH of different liquids. Let cool and pour through a strainer into a large jar. Add a few drops of the cabbage juice to each solution and note any color changes. The juice should turn pink in acidic solutions, green in basic solutions, and not change in neutral solutions. Try some other solutions of interest.