Re: [Phys-L] checking the work for minus signs ... et cetera

[Bernard Cleyet <bernard@cleyet.org>]

On 2015, May 11, , at 13:26, John Denker <jsd@av8n.com> wrote:

> Tangentially related idea:  Checking the work is
> a Big Deal.
>
> The obvious way to check the work is to redo the
> calculation, checking and re-checking each step
> along the way.


Additionally:  separating the parts, combining, and then comparing to the initially all in "one go”.  

A recent example:  The Cambridge Clock (Trinity College) has been examined in detail in order to ascertain if it can detect the g variation due to the moon.  (1)

My interest is in its running Q.  The escapement supplies energy (to the pendulum) from the drop of the gravity arm;  mass 50 g thru 3mm every 1.5 seconds. (three second period)

The bob's mass is 104 kg  (calculated from other data, i.e. not measured directly), and the running amplitude is 55mrad.  


Inserting the numbers all in one go into the definition has the advantage of canceling the factors 2 and g. 

The alternate is to separately find the pendulum’s energy and divide it by the escapement energy.   

This is a method described by Woodward (2) in, IIRC, "My Own Right Time” to fins the running Q.  

bc,  necessitated doing several times to obtain agreement with both methods.  

p.s. Assumptions and approximations include:   zero rod mass and bob a point.  And I did not obtain the published value from the keeper of the clock reported by Drumheller. (3) (bc=> 7358  Dr. Hunt, fellow Trinity College:  4570)  


(1)  Lupton, R.     The Trinity Clock   

http://trin-hosts.trin.cam.ac.uk/clock/?menu_option=theory  

(2)  Philip Woodward - Wikipedia, the free encyclopedia  http://en.wikipedia.org/wiki/Philip_Woodward  

(3)  Drumheller, Douglas S.;   Barometric compensation of pendulum  JAM-11-1236 (copy supplied by the author.  The shorter article in the HSN doesn’t include this information.)