Re: Poms view of the Gilly debate

In message <f23308$80f$1$8300dec7@xxxxxxxxxxxxxxxx>, Dr A. N. Walker <anw@xxxxxxxxxxxxxxxxxx> writes

Well, OK, but although I don't recall much mention of
cricket [or football, tennis, golf, ... for that matter] in the writings of Galileo and Newton, this is basically pure Galileian mechanics with a dash of Newtonian, and well within the bounds of A-level maths+physics. Doesn't even need calculus. There must be a reasonable number of readers with that knowledge, and many more who could at least appreciate the results.

Let us pray you never taught schoolchildren. Rh
#
Here is your starter for ten. A brick wall will work quite
well at "hitting" a ball bowled at it. Would you expect a rubber
wall to work better, or worse? Give reasons.
Not so sure how that is relevant.

Well, for a start, there is *no* [relevant] energy or
power stored in the wall, so it's a simpler problem -- always a good starting point. Secondly, a Galileian transformation* turns it into a moving wall. After that, you can start to think about a *light* moving wall, which you can call a "bat" [or a "club"] if you like. Mere words.


Big difference between a bat and wall: the bat moves. RH

For example, you can "easily" find the angle of loft
at which you need to hit the ball -- cricket or golf -- for a drive to have maximum range. Left as an exercise. You lose most of the marks if you assume the answer involves 45 degrees.

As to the rubber -- would you expect a ball to bounce
further off a brick wall or one made of squash balls [which would therefore compress and store energy, and, according to the arguments up-thread, enhance the power of the wall]. Why? What determines the strength of bounce? [You can use a floor rather than a wall, if it helps you to find rubber ones. Mere words again.]

Frankly I don't know but let's see if a bit of reasoning will give the answer. The brick wall will deform less when receiving the ball so perhaps the ball bounces back more vigorously because less of its energy is absorbed by the wall than happens when the ball hits a rubber wall. However, I suppose that the different qualities of rubber and brick might mean the rubber utilises the energy received from the ball more effectively to thrust the ball from it. RH

What kind of rubber? What
configuration of wall? How do you mean "better"?

Sorry, those are unbounded questions, you'll have to
ask elsewhere.

Actually they re not. They are questions which can be answered exactly by defining the nature of the wall. Poor old bound mind, quite incapable of understanding its limitations. RH

[Didn't they teach you not to argue with the examiner?]

* This is just Galileo's observation that mechanics on board a smoothly-moving ship is exactly the same as it is on land -- you could play [French?] cricket in your cabin and not notice the difference. So if you know what happens to a ball and a stationary wall/bat/club, you can just add the same velocity to every part of the experiment to know what happens if the wall/bat/club is moving.

--
Andy Walker, School of MathSci., Univ. of Nott'm, UK.
anw@xxxxxxxxxxxxxxxx

--
Robert Henderson
Blair Scandal website: http://www.geocities.com/ blairscandal/
Personal website: http://www.anywhere.demon.co.uk
.

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