27 January 2022

# Here is another problem to be solved

Now that we have solved the temperature problem in Chicago, here is another one from San Francisco.

[Errata: Looks like I have completely forgotten my physics – Sound is longitudinal and light is transversal – it is about which way the wave is moving and the particles in the wave are moving.

However, my original question remains – although I cannot remember the terms now – a ray of light goes straight but sound disperses in all directions – like the pool analogy. So, how does this work?]

Last week, I was in San Francisco and as his is wont, Matt Moore invited me to go for a walk with him by the waterfront and discuss business issues. While walking around Pier 15 enjoying some nice coffee, he showed me something. It is basically a set of two parabolic metals facing each other about 50 yards away. Each has a small stool to sit on. Matt asked me to go sit on one and he sat on another. As you can see in the picture.

Some of you might have guessed this, I could distinctly and loudly hear what he was saying. It felt like he was just six inches behind my head and he was talking to me from there with a slightly louder than usual voice of his.

For the next few minutes, I showed off my Physics to Matt by eloquently explaining how we were sitting in the focal points of the parabolas and how his voice was hitting his parabola, going then in a straight line to my parabola (geometric property of parabola if you remember) and then my parabola was putting all that on to its focal point which is where I was sitting. You would have seen the same in microwave towers, large telescopes etc. I do not know what Matt thought but I thought I did a good job.

Two days later, I realized what an idiot I was. I was telling Sharmila about it and then half way thru, I stopped cold. I realized that everything I said to Matt was correct but only for longitudinal waves – you know like microwaves, light etc. But sound is a transversal wave. It spreads out in concentric circles (like if you throw a stone in still pool). Those sound waves from Matt would have emanated as concentric circles and then after some of them hit the metal parabola, they would start out as more concentric circles from the point of incidence (where it hit the metal). Then where is the question of focus and all that in an ellipse?

But I experienced it myself.

How do you explain that?

Posted January 27, 2022 by Rajib Roy in category "Puzzles", "Travelogs