Monthly Archives: May 2026

May17

Pressure is Isotopic: It Has No Preferred Direction

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Pressure Is Isotropic

Why Pressure in a Fluid Acts Equally in All Directions

One of the most fundamental results in fluid mechanics is:

At a given point inside a stationary fluid, pressure acts equally in all directions.

This property is called the isotropy of pressure.

At first glance, the statement appears intuitive. Yet it emerges from a deep physical requirement: a fluid at rest cannot sustain shear stress.

The Core Physical Idea

Unlike solids, fluids cannot resist continuous tangential deformation. If unequal directional stresses existed at a point inside a stationary fluid, the fluid element would experience a net turning or shearing effect.

The element would then deform and begin to flow.

But a stationary fluid, by definition, is in equilibrium.

Therefore:

No directional imbalance can exist inside a fluid at rest.

Pressure must therefore act equally in every direction.

The Conceptual Proof

Consider an extremely small fluid element inside a liquid at rest.

Suppose pressure along one direction were greater than pressure along another direction.

The larger pressure would produce a greater force on one face of the element, generating an unbalanced shear tendency. Since fluids cannot sustain shear stress in static equilibrium, motion would immediately begin.

This contradicts the assumption that the fluid is stationary.

Hence the only possible equilibrium condition is:

Thus, pressure at a point in a static fluid is isotropic.

An Important Consequence

Because pressure has no preferred direction:

  • fluids exert force perpendicular to surfaces,
  • Pascal’s law becomes possible,
  • and hydraulic systems function efficiently.

From ocean depths to hydraulic lifts, isotropic pressure governs the behavior of fluids everywhere.

Final Conclusion

Pressure in a stationary fluid is isotropic because any directional inequality in pressure would create shear forces and destroy equilibrium. Nature preserves stillness inside fluids by ensuring perfect directional balance.

May13

Gratitude from IIT JEE Topper AIR 1 – Rajit Gupta to Devansh Sir

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Some journeys begin with talent. Others begin with the right guidance at the right time.

Rajit Gupta first joined my NSEJS batch as a young student in 9th grade with curiosity, sincerity, and a willingness to learn deeply. Over the years, that curiosity evolved into extraordinary achievement — culminating in an exceptional academic journey that includes AIR 1 in Joint Entrance Examination – Advanced, 100 percentile in JEE Mains, selection in multiple prestigious Olympiad camps, qualification for International Physics Olympiad, and selection for APhO twice.

What makes Rajit’s journey especially meaningful to me is not only the scale of his achievements, but the depth of understanding and intellectual maturity he developed along the way. His testimonial beautifully reflects the philosophy I have always believed in — that true Physics education is not about memorization, but about intuition, clarity, imagination, and genuine curiosity.

I am deeply proud of Rajit and grateful to have witnessed his remarkable journey from a young Olympiad student to one of the finest performers in the country.

Respected Devansh Sir,

I am Rajit Gupta. I was your student in NSEJS batch in 9th grade. This year I appeared in JEE and I have got Rank 1 in JEE Advanced, 100 Percentile in JEE Mains, and very good scores in NSEP and NSEA.

I wish to express my deepest gratitude for the immense impact you have had on my journey.

When I started learning physics in your classes, it was completely new to me. But instead of just making me memorize concepts, you motivated me to truly understand them. Your guidance not only helped me build strong intuition but also sparked a genuine interest in the subject.

What sets you apart is the effort and dedication you put into each of your students. Your well-thought-out resources, insightful suggestions, and constant encouragement played a crucial role in my growth. Thanks to your support, I was selected for the Junior Science OCSC, Astronomy OCSC and later for the Physics OCSC twice. I qualified for IPhO this year and also got selected for APhO two times (although I wasn’t able to attend the event this year due to my JEE).

Looking back, I realize that without the strong foundation you gave me, none of this would have been possible. You gave me the perfect kickstart, and for that, I will always be grateful.

Thank you very much, Sir!

Best regards,
Rajit Gupta

May13

“Physics Started Making Sense” — A Heartfelt IIT Bombay Student Testimonial

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Sometimes, even a few months of the right guidance can completely transform a student’s confidence and way of thinking. Palak Sanadhya joined my classes only a short time before JEE Advanced, yet her sincerity, hard work, and deep commitment toward conceptual understanding helped her secure admission to Indian Institute of Technology Bombay in Chemical Engineering.

What makes her testimonial especially meaningful to me is that it reflects the very philosophy with which I teach Physics — not as a collection of formulas to memorize, but as a subject to be visualized, understood intuitively, and appreciated deeply. I am grateful to have played a small role in her remarkable journey.

Securing admission to Chemical Engineering at Indian Institute of Technology Bombay after clearing one of the most competitive examinations in the country was a dream come true for me. And although I studied under Mr. Devansh Mittal for only around three months before JEE Advanced, the impact of his teaching during that short period was truly remarkable.

What immediately stood out to me in his classes was the way he approached Physics — not as a subject to be memorized, but as something to be deeply understood and mentally visualized. In an environment where students often focus only on speed and formulas, his teaching emphasized imagination, intuition, and conceptual clarity.

Whether it was Mechanics, Thermodynamics, Waves & Oscillations, Electrodynamics, Optics, or Modern Physics, he explained every topic with extraordinary precision and simplicity. Even concepts that had previously felt confusing became intuitive after his explanations. His ability to connect physical understanding with mathematical problem-solving made a tremendous difference in my preparation.

One of the most unique aspects of his teaching was his belief, inspired by Albert Einstein, that imagination and intuition are just as important as logic in learning Physics. Instead of encouraging rote methods, he trained us to think independently and understand the deeper meaning behind every concept. That approach not only improved my problem-solving ability, but also gave me confidence while attempting challenging JEE Advanced questions.

Beyond academics, I was deeply touched by the sincerity and honesty with which he guided his students. He genuinely cared about our progress, regularly communicated with parents, and ensured that students remained disciplined, motivated, and mentally focused during such an important phase of preparation.

Despite the limited time I spent under his mentorship, his guidance had a lasting impact on my understanding of Physics and my confidence as a student.

Mr. Devansh Mittal is far more than an excellent teacher — he is a mentor who inspires students to think deeply, learn sincerely, and believe in their own potential.

I will always remain grateful for his support and guidance during one of the most important phases of my academic journey.

— Palak Sanadhya

May13

“I Have Not Seen Such High-Quality Lectures Before”: An IIT Delhi Professor’s Remarkable Testimonial

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There are moments in a teacher’s journey that become deeply meaningful — not merely because of praise, but because of the source from which that appreciation comes.

Receiving a heartfelt testimonial from Prof. Saif Khan Mohammed of Indian Institute of Technology Delhi was one such moment for me.

Prof. Saif is not only a distinguished academician from the Department of Electrical Engineering at IIT Delhi, but also someone who himself secured an under-100 rank in IIT-JEE during his student years. His deep understanding of Physics, analytical thinking, and exposure to high-level technical education make his words especially valuable and humbling.

What touched me most was not simply his appreciation of my lectures, but his recognition of the philosophy behind my teaching — beginning from first principles, developing intuition step by step, and helping students gradually build the confidence to solve highly challenging problems, including advanced problems from the legendary book by I. E. Irodov.

As educators, we often strive not merely to teach formulas, but to cultivate curiosity, clarity of thought, and genuine understanding. To know that these efforts resonated with a respected IIT Delhi professor and benefited his daughter deeply is something I will always cherish.

I am sharing his words below with immense gratitude and humility.

Dear Shri Devansh

I am Prof. Saif Khan Mohammed, Dept. Electrical Engineering l.I.T. Delhi. My daughter is enrolled in your online course. I have been personally viewing your physics video lectures and I must say that I have not seen such high quality lectures before. My daughter has seen other online lectures, but none of them are as good as yours. After seeing your lectures she was able to solve difficult problems in Mechanics from the book by I. E. Irodov. The way you start any topic from basics and gradually increase complexity is what makes it easy for students to learn physics with so much ease. I thank you for your great contribution to education and I am sure you will make even greater contribution in the years to come.

Prof. Saif

IIT Delhi

—

Prof. Saif is a learned professor at IIT Delhi. He himself had under 100 Rank in IIT-JEE when he appeared into it.

https://iitd.irins.org/profile/70117

May9

MIT, Stanford, Oxford & Beyond — Rudra Pethani’s Gratitude for Devansh Sir

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Rudra Pethani is one of the most exceptional young students I have had the privilege to teach. His remarkable journey reflects not only extraordinary intelligence and hard work, but also deep curiosity, discipline, and a genuine passion for learning.

Rudra represented India at the 20th International Junior Science Olympiad (IJSO) held in Thailand and brought immense pride to the nation by winning a Gold Medal. Over the years, he has consistently demonstrated outstanding academic excellence and an exceptional ability to think deeply and intuitively about science and problem solving.

Today, his achievements have earned him acceptance into some of the finest universities in the world — including MIT, Stanford University, Oxford University, and Imperial College London — an accomplishment that very few students across the globe achieve.

What makes Rudra truly special is not only his brilliance, but also his humility, sincerity, and relentless desire to understand concepts at their deepest level.

Below is a heartfelt testimonial written by Rudra about his learning journey and experience with my physics mentorship.

My name is Rudra Pethani, and I am studying in Allen Career Institute.  

I came in contact with Devansh Sir in January 2024 for the INJSO Online Workshop, and I have been his student ever since. He has a completely different and unique approach to physics that I had never seen before. His clear and concise manner of speaking makes each and every student understand what he is trying to convey to us. Moreover, his systematic and methodical approach towards problem solving and concept building has really helped me get a strong grasp on the entirety of physics. The emphasis given to intuitive learning of all the various topics has helped me gain confidence and given me the ability to solve even the toughest of problems. 

I would like to thank Devansh Sir for imparting his vast knowledge to me. Without his guidance, I do not think I would have been able to get this wonderful achievement.