Rinse out the soda bottle and cap to make sure it is clean.
Fill the bottle three-fourths of the way full with vegetable oil. Fill the remainder of the bottle with water. The bottle should be full, but not overflowing.
Add 10 to 20 drops of food coloring to the bottle. The amount of drops may vary depending on the color you choose for the project. Darker colors, such as blue, green and red, will take less color than lighter colors, like yellow, to show up.
Cut the effervescent antacid tablet into eight small pieces. Drop the first piece into the bottle. The mixture will bubble. When it stops bubbling, drop another piece into the bottle. Repeat this until all of the pieces have been dissolved into the mixture.
Screw the cap onto the soda bottle. Illuminate the bottle with your flashlight. This project works because the liquid (water, food coloring and dissolved antacid tablet) bonds together into a "lava blob." The oil is lighter than the liquid and forces it down to the bottom of the bottle. When you tilt the bottle onto its side and rock it back and forth, you'll see a "lava wave."