A water tornado, or vortex, is a swirling mass of fluid that forms a funnel shape with a low-pressure area at its center. This phenomenon occurs when water moves in a circular path, causing it to spiral inward. Creating a controlled water vortex is a simple science demonstration that illustrates rotational fluid dynamics. The experiment uses common household materials, making it an accessible way to explore the physics of natural occurrences like tornadoes and whirlpools.
Creating a Vortex with Two Bottles
The most effective method for producing a sustained water tornado involves joining two standard two-liter plastic bottles. Begin by filling one bottle two-thirds to three-quarters full with water. For enhanced visibility, a few drops of food coloring or a pinch of glitter can be added.
Next, the two bottles must be securely connected mouth-to-mouth at their openings. This connection can be made using a specialized connector tube or by creating a watertight seal with a flat washer and strong duct tape. Ensuring the seal is watertight prevents leaks when the assembly is inverted and the full bottle is placed on top.
The crucial step is to initiate the rotational movement by grasping the connected bottles and swirling them rapidly in a horizontal circular motion. This spinning action causes the water to move along the bottle’s inner wall, forming the characteristic funnel-shaped water tornado. This method allows the water to drain quickly and dramatically into the bottom bottle, maintaining the vortex for several seconds.
Producing a Whirlpool in a Single Container
An alternative method for observing a smaller, more temporary vortex involves using a single container, such as a large glass jar or deep plastic cup. Fill the container with water, leaving a few inches of space at the top to prevent spillage.
The whirlpool is generated by introducing a rapid, continuous circular motion to the water using a long spoon or stick. Stirring must be maintained for several seconds to impart sufficient rotational energy. When the stirring implement is removed, the water continues to spin briefly, and a small, temporary depression appears in the center.
This single-container vortex is less dramatic than the two-bottle version because the water is not draining through a narrow opening. The swirling effect quickly dissipates as energy is lost to friction against the container walls and air. It serves as a rapid demonstration of how mechanical energy creates a rotating fluid mass.
The Physics Behind the Spinning Water
The formation of the water tornado demonstrates several principles of physics, primarily angular momentum and fluid dynamics. When the water is swirled, it gains angular momentum, the rotational equivalent of linear momentum. As the water spirals inward toward the center opening, its speed increases.
This increase in speed is due to the conservation of angular momentum, similar to how a spinning ice skater increases rotation speed by pulling their arms closer to their body. The swirling motion causes the water to be thrown outward against the bottle walls by centripetal force. This action clears a path in the center, forming a hollow, vertical column.
The resulting central column is where the physics becomes most apparent. It allows air from the lower bottle to rush up into the top bottle. Without this clear air passage, the water would drain slowly in a disruptive “glug-glug” manner as the water and air struggle to exchange places. The continuous, hollow air column facilitates a smooth, rapid, and sustained flow.