Liquid that spins in a circular motion forms a whirlpool. A vortex is a whirlpool with a downward draft. Whirlpools occur most frequently when water is forced through a narrow opening and then flows into a more open area. The water speed increases as it goes through the opening, creating a whirlpool downstream. Whirlpools can also occur in the ocean where water flows through narrow straits, particularly when the tide is changing. A model of a whirlpool or vortex can be created with simple items around the home.
Remove the tops from both bottles. Fill the first bottle ¾ full of water. Add a few drops of food coloring.
Hold the second bottle above the first with the bottle openings together. Use the duct tape to join the two bottles together securely. Tip the bottles so the water flows over the joined section to verify no water leak occurs. If water leaks out add more duct tape.
Create a vortex. Turn the connected bottles vertically so that the bottle with the water is above the empty bottle. Swirl the bottles in a circular motion as fast as possible. A whirlpool will form in the top bottle as it drains into the bottom bottle.