Do-It-Yourself... Ocean in a Bottle

What You Need

Food coloring

Water

Baby Oil or Mineral Oil

16 oz. Plastic bottles

Small objects: Cork, Plastic Starfish, Shells, etc.(optional)

What You Do.
Fill a small plastic bottle slightly less than 1/2 full with water. Fill the bottle to the top with mineral oil or baby oil. Add about 4 drops of food coloring. You may add small pieces to the bottle to make your ocean more interesting and see how objects of different weights move in a wave. After placing everything in the bottle put the cap on tightly (you may want to glue or tape the cap shut to reduce the chance of spilling). Turn the bottle on its side and gently rock the bottle to produce waves. Do your objects float or sink in the water and oil? Observe the changes that take place if you shake the bottle vigorously and then allow it to sit for a few minutes.

What’s Going On Here?
When you rock the bottle from side to side, a pattern resembling waves is produced. In oceans, rivers, and lakes, most waves are caused by wind, and move across great distances without changing much in terms of shape or energy. Waves are the result of a transfer of energy from one water molecule to the next. In one complete wavelength, a molecule of water moves in a circular path and ends up at about the same place that it started. Objects floating on the water’s surface may move horizontally slightly, but mostly they bob up and down as waves pass through the water. At this point, the waves they are called swells. As they approach shallow water, the circular motion of the water particles in the wave becomes more elliptical. Wavelength decreases and steepness increases. The velocity of particles at the crest increase with the height of the wave and eventually the wave is said to break.

The ocean in a bottle activity also demonstrates what happens when an oil spill occurs at sea. Since oil and water do not mix, the oil will never completely combine with the water. You can observe this by shaking the bottle vigorously. Because oil is lighter than water, it will remain at the surface. From your observations, can you think of a way to clean up an oil spill? The objects you placed in the bottle all have different densities. If an object is not as dense as the oil, yet denser than the water, it will float between the oil and water. Can you determine the relative densities of your objects by observing whether they sink or float?