When will the Earth stop spinning? A question to a high school student ...

Updated: Apr 27


In January 2019, while watching a documentary about how the Solar System and the planets were formed including our very own, the Earth and its closest neighbor, the Moon, I fell far deep in thoughts of whether I could derive mathematical equations and get the numerical values of the quantities mentioned in the documentary. I also asked myself whether I could do all these by using only high school physics knowledge. The documentary pointed out that

  1. The Earth - Moon system was about 4 billion years old and the Moon was at a distance of a few tens of thousands of kilometers from the Earth by then.

  2. The Earth was spinning (i.e rotating about its own axis) so fast that one full day would take only about 6 - 7 hours about 4 billion years ago.

  3. Due to tidal forces, the Moon has been slowing down the Earth’s rotation about its own axis.

Amazed by this documentary, I pondered the slowing of Earth’s spin problem over that night, without making any attempts to solve it till following morning … a great strategy I have adopted for years: thinking first, rushing into the solution second. I would say, the most important phase of the solution process of a science problem is the very first one where the problem is contemplated and comprehended, which involves lots of intense thinking … Then, I have put together this study for the benefit of all who are interested in understanding the Universe.

This study also demonstrates the power of high school level knowledge to predict the PAST (i.e billions of years ago) and the FUTURE (i.e billions of years from today) of a dynamical system, here is the Earth’s spin motion. I hope it will also boost the motivation of students who would like to pursue their careers in one of the STEM (Science, Technology, Engineering, Math) fields.

The study here reveals that using basic Physics knowledge, anyone can show that

  1. One Earth day will be 100 years 5 billion years from today and the Earth will most likely stop spinning in 7.5 billion years.

  2. The Moon was much closer to the Earth when it was first formed about 4 billion years ago (of the order of few tens of mega meters)

  3. The Earth was spinning much faster in the past. It is very likely that one Earth day was less than 10 hours 3 billion years ago.

"This study demonstrates how much an interested, hardworking and curious science student even at high school level can do with a limited amount of physics and math knowledge. In most occasions, science students do not know or realize that what they learn in science classes are applicable to real life. There is a lot in the knowledge they acquire through their studies, way more than what they can mostly anticipate. This study was created to serve for the purpose of proving that knowing science, yet very little, can make one extremely powerful in making scientific predictions about the dynamics of the Universe. So, when we attend a science talk, or watch a science documentary on TV, or read a blog post about science on the web, we can always be aware that all results being presented to us may have basis on some basic principles. Here, our intention is not to undermine the hard work of the scientists, but to make all realize how valuable each piece of information is in creating knowledge and finding scientific results."


#science #astronomy #stemeducation #physics

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