# Do you know 127 year old Physics Riddle is solved? What was that Riddle?

Have you ever noticed that while rearing a boat, wave’s ripple out which is known as wake. According to science since 127 years, the long uniformity of waves forms v-shape at an angle of exactly 39 degrees. It does not affected by the size of the vessel, speed or motor’s power. But now, a physicist proved this theory with other angle. Let us understand the science behind it.
Aug 22, 2019 17:51 IST
127 year old Physics riddle is solved

According to science, for 127 years, in water waves spread out in the form of triangle which is known as Kelvinangle. But recently, a Norwegian scientist challenged the theory and discovered that there is a current underneath the water and so, the angle changes. Let us understand it in detail.

The story behind the theory: An associate professor at the Norwegian University of Science and Technology's Department of Energy and Process Engineering namely Simen Adnoy Ellingsen challenged the theory of Kelvinangle in boat wakes. This theory was named after Irish physicist William Thompson, later known as Lord Kelvin. According to the Kelvinangle theory, in water waves spread out in a triangle.

While challenging Lord Kelvin's theory, Ellingen realised that he was going against history.

How Ellingsen solved the riddle?

He took the help of several genius people like Augustin-Louis Cauchy, Poisson and Kelvin to solve this wave riddle and took lot of effort even for the simplest case of still water without currents.

What are Waves?

To understand the riddle, it is necessary to know about shear flow: Boat wakes have different angle under certain circumstances and can even be off-centered with respect to the direction of the boat. This can happen when there are different currents in different layers of water which is known as shear flow and Kelvin's theory on boat wakes for shear flow is not applicable.

Further Ellingsen also predicted about Oblong rings that is under certain circumstances ring waves also act funny. When you throw a pebble in a lake on a peaceful summer's day then the pattern of the wave will be perfect that is concentric circles. But it will not be perfect if there is a shear flow. Then the rings might turn into ovals. He further expands Cauchy and Poisson's theory.

After doing Lab Research, Ellingsen ended up this theory in the Journal of fluid Mechanics.

Note: He has done all his calculations on the paper so, it is yet to be observed empirically.

He took around six months to do research in the lab.

The result that is published in the Journal of fluid Mechanics is that a large portion of fuel on ships actually goes into making waves. Further Ellingsen added that the consumption of fuel can be doubled of the vessel is travelling downstream as compared to upstream. These calculations are done on the currents at the mouth of the Columbia River in Oregon in the U.S. because, here the currents are strong and the boats were also in large quantity.

Therefore, the research on boats and ships in different currents is necessary to see the impact of reducing fuel consumption and consequently emissions.

At last, Ellingsen told that his theory doesn’t disprove Kelvin's theory but he had just extended it.

Kelvin's theory is true as long as there are no current layers under the surface when the water is deep.

But when there is a movement between the layers of water then different layers move at different speeds and the angle changes. He told that with extremely strong currents moving perpendicular to the direction of the boat, the wake can actually end up in front of the boat on one side. Then a person should go sailing somewhere else.

Ellingsen said that charge waves that strike gold surface to produce easily manipulatable tracks.

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