Tennis Serve Physics

On a kick serve, the racket meets the ball at high speed, with the ball literally sliding down on the racket strings for several inches before it leaves the racket. The strings themselves stretch for as much as an inch at the impact.

This is why there’s a ‘sleight-of-hand magic’ to the kick serve. The racket continues its path ‘beneath’ the ball, which at first has near-zero velocity; in slow motion, you can see that the racket head ‘moves ahead’ of the ball just immediately after impact. The server may get the feeling that he has caught the ball and is then ‘pulling the ball down’ as he continues with the serve’s follow through. (In fact, he has hit up on the ball, but with the racket on a circular path, which is why the follow-through is to the side, rather than forward.) The ball initially travels up and then arcs down because of gravity and spin.

All this happens because the body is sideways (not facing the net), and bent at the waist so that the swing path is left to right in relation to the body but ‘up and over’ in relation to an imaginary vertical line ending on the ground. The ‘up and over’ motion also reflects the ‘shoulder over shoulder’ rotation that creates the power for the serve.

References

From Popular Mechanics

https://www.popularmechanics.com/adventure/sports/a2072/4221210/]

Pancho Gonzalez’s serve on YouTube

https://youtu.be/tyhFo3hvGPI

Economics 2.0

THE MEANING OF SOCIAL ORDER

IF there is dumb, there’s dumber; smart, smarter; thievery, plunder; good, saint; plain Jane, invisible; pretty, beauty; etc.

The point is that we can use these gradations to better understand economics.

When you do things for status, that’s social order driving the economy.

But what kind of good is status? It’s not rival, because you can’t eat it; but it’s exclusive. A club good?

Citizenship is a club good. So is formal education. So is the opinion of your peers. We strive for and shed these things, depending.

And that makes the economy, micro or macro, somewhat unpredictable. Yet, understandable.

Perhaps status is an informal club good, akin to Groucho’s inexistent club. And as an informal club good, status is like fiat money, valuable only on the prevailing whim of a society that confers that value.

But unlike fiat money, status can’t just be printed. There is no central bank that can create status.

This kind of thinking leads us nowhere, doesn’t it? Still, better to know that we’re not anywhere, than to pretend we’ve arrived.

Economics as science, and is science “art”?

Is economics a science?  How does it differ from religion? In a lecture, I tried to answer these questions.

A more general question is: Is science art?

I answer in the affirmative because science requires not just theorizing and empirical testing but also choosing from alternative theories.  The choice, usually based on Occam’s Razor, is art.  This is not new.  Supposedly, it harks back to Nietzsche and was well elucidated by Popper with the concept of “falsifiability” as being inherent in science.  What this means is that you can’t falsify without having a priori a choice of which theories to attempt to falsify.  That a priori choice is, obviously, neither predetermined nor itself “falsifiable,” if only because the universe of possible theories is an unlimited set (and such a set would by definition not be fully knowable).

Desultory Serendip – just a piece of poetry

Almost Six Years

Sometimes I wonder

Other times I wander

Or else I ponder

– not that it’s a bother –

Why it is we suffer…

****

No pain, no gain … at the gym

Pain et vin at Le Cuillere

With the mussels and the duxelles

And bananas and ananas,

Wishing for the painted wall to be replicated

Down Tambobo way, yes!

****

But in the end, the suffering means little

Just a bump here and there

Or a slow grind for the decaf.

We dance and sing in the sun and rain

Like raisin and nuts looking for M&Ms.

****

Paris – Food to eat, and food for thought

Two books on my bookshelf are must reads.

One, Remembrance of Things Paris: Sixty Years of Writing from Gourmet, edited by Ruth Reichl (2005), deals with cuisine. It includes a two-sentence recipe for mushroom duxelles in a piece by Louis Diat on “Cuisine Parisienne.” The book is peppered by literary tidbits, all in the context of the history and geography of the city. Read the book for the flavor.

The other, The Most Beautiful Walk in the World: A Pedestrian in Paris, by John Baxter (2011), is a celebration of how to visit Paris. You know that you need this book when, like me, you first read how it ends. This is the last paragraph and sentence of Baxter’s book:

Then, if you think you can stand the romantic rush, climb the famous stone staircases of Montmartre around 5:00 a.m. or take the little cable car, buy coffee and rolls, and eat breakfast on the terrace below the Cathedral of Sacre-Coeur. If the harpist is there, drop a euro into his hat and ask him to play “Jeux Interdits.”

C’est tellement simple, Paris.

‘Circuses of the Surreal’

What is wrong with Patricia Evangelista? Many people consider her a brilliant writer. The brilliance shows in her latest op-ed.

Yet, still, somehow, I’m not a vendee. Evangelista concludes that a respondent in a court proceeding betrays the public trust by asking for presumption of innocence and seeking judicial review on the belief that the court has over-reached. I submit however that legal parries and the accompanying PR spin do not amount to betrayal of public trust. The man is simply trying to survive.

The respondent may well be guilty, but still the pro reo principle holds. You still have to give him his day in court – there is a due process requirement albeit limited because life, liberty, or property is not at stake.

And if he’s innocent, all the more does he deserve to ask for his constitutional rights.

What is probably more correct than Evangelista’s colorful pushes on English is simply this: That if you protest too much, you lose.

The real damage to Chief Justice Corona’s position is not from the ‘let-me-join-the-bandwagon’-while-being-cute style of Evangelista. Nor even from the more general sense that the impunity show should come to an end.

The damage comes from the abundant sneer emanating from his counsels. If a somewhat distracted observer can sense that they think the rest of us, including the judges, are hicks because we don’t know the basket-weaving of remedial law, then the political kick does kick in. The Senate may well convict if only because it has been insulted. That’s the tragedy of the case if the respondent deserves an acquittal; it’s karma otherwise.

Art at a festival in DC

By Daniel Roncesvalles and Associates.