Super Spirals

Fragile seaweed can survive storms by adopting a spiral shape.

Seaweed has found a way to deal with heavy seas and storms. It forms a spiral shape that follows the path of least resistance. A spiral is a curved shape that winds around a central point, axis or line. There are many different types of spirals, each with their own unique properties and characteristics. In nature, spirals are commonly found, for example in snail shells, where they serve functional purposes such as protection or movement.

Inventor and entrepreneur Jay Harman noticed spiral-shaped seaweeds as a child and got intrigued by the spiral shape geometry that can be found in many places in nature: from water flows, to shell architectures, the shape of some antlers, sunflowers and even our own DNA. As an adult, he studied the mathematics behind how fluids flow and applied it to create devices that use far less energy and material than existing ones.

What is the effect of water movement on its speed?

• Organise pupils into groups of 3. Give two pupils a (plastic) bottle with water and one a timer.
• The two pupils with the bottle start a competition to get the water out of the bottle as fast as they can. Pupils 1 tries to get the water out by shaking the bottle up and down; pupil 2 by moving the bottle in circles (like a spiral).
• Who is the first to have an empty bottle? Why do you think this happens?

Simple explanation

Why water flows in a spiral?

You can see water flow in a spiral when you unplug a full bath to let the water drain. Before you open the drain, the water already has some motion, although probably too slow to notice. When you unplug the bathtub, the motion of the water is accelerated because it has to pass through a narrower channel. The water falling into the drain then moves faster than the water further away from the drain. When the water in one place is moving faster than it is in another place, it starts to spin. The curvature of the flowing water then begins to form a spiral. This type of spiral, where the curvature increases in distance as it circles around a point, is also called a growth spiral.

More detailed explanation

As the water spins, it creates a low-pressure area in the center of the circle. The low-pressure area sucks in more water from the surrounding area, which makes the spinning water go faster and faster. This phenomenon is known as a vortex, which is a swirling flow of fluid that rotates around an axis.

The size and behavior of the vortex in a draining bathtub can be influenced by several factors, such as the size and shape of the drain hole, the viscosity and temperature of the water, and any obstacles in the flow. Understanding vortices and their behaviour can be important in fields such as fluid dynamics and hydraulic engineering, where they play a role in many real-world applications.

How spiral shape helps seaweed

Kelp, a type of large brown seaweed, moves in spirals due to the movement of ocean currents. In oceans, water is subjected to strong currents and waves. When water moves around the kelp, it creates friction, causing the kelp to sway and bend. Over time, the repeated bending and swaying of the kelp can cause it to grow in a spiral pattern, as it tries to find the path of least resistance in the flow. This spiral growth can be influenced by various factors, such as the direction and strength of the currents, the presence of other underwater structures, and the biology and physiology of the kelp itself.

The spiraling growth of kelp can have various ecological benefits. As described above, it helps kelp to better withstand the forces of ocean currents and waves, which can reduce the risk of damage and increase its overall survival. Besides that, the spiral shape can increase the surface area available for photosynthesis, and improve the ability of the kelp to absorb nutrients and sunlight.

Inspired by the flow patterns of water in nature, Jay Harman created the lily impeller: a pump that mimics the flow pattern of vortices with a series of blades arranged in a spiral pattern. Due to the spiral-shape of the blades, they create a smooth, non-turbulent flow of water as they rotate. Because the impeller can rotate with minimal energy input, it reduces the amount of energy needed to mix and circulate water. This reduces any environmental harm from the use of energy, while also saving money. Additionally, because it is designed to create a gentle flow of water, the lily impeller can help to reduce the risk of fish or other aquatic life being harmed by strong currents or turbulence in the water. The resulting lily impeller has been used in a variety of applications, including water treatment, wastewater treatment, and industrial processes.

Some STEAM opportunities include:

• Understanding the relationship between structure and function.
• Identify how plants are adapted to suit their environment in different ways and that adaptation may lead to evolution.
• Asking questions and making observations.
• Carrying out simple tests.
• Making predictions.
• Apply learning to real world problems.

Watch a video of Jay Harman's lily impeller (watch here).

More explanation about water vortices (read more here).

Watch how kelp moves in the ocean (watch here).

Watch how water turbines are being invented based on the principle of vortices (watch here).