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

John, Brian
- People who must be cutting material to build stuff do this all of the
time - making multiple measurements of the same thing - since they have
learned the hard way and wasted a lot of material.
- And sometimes we will measure using a different "stick."
- And sometimes we will do it all in our heads just to see whether the
measurements make sense.
- One must be really careful on a milling machine, for example, to
distinguish between an end mill's radius and diameter, and to figure out
whether one must add to or subtract from a measurement.
- The Cat that stays with me by choice (she has a window flap and jumps out
the window whenever I get on keyboard) regularly makes jump calculations
and sometimes screws up and drops the entire cat onto the floor, but her
calculations tend improve for any particular jump situation.
- This same cat, trotting along a tree branch I have placed just below the
ceiling will sometimes assume that the back of the cat will follow the
front of the cat on a crooked branch, and sometimes she is wrong and falls
- but learns. Same goes for human calculating.
Bill Norwood, U of MD at College Park

On Fri, May 15, 2015 at 3:06 PM, brian whatcott <betwys1@sbcglobal.net>
wrote:

Bernard,

I replicated your value for Q given the following assumptions which I
presume you made:
1) the effective pendulum length l is obtainable from Period = 2.Pi.
root(l/g)
2) The value for g at Trinity is 9.8 N/kg. The pendulum amplitude is
55mr.
3) The maximal value for pendulum energy occurs at the potential energy
max.
4) Infinitely rigid, lossless pivot

If I choose instead the moment where angular displacement = 0 mr
and an escapement increment has occurred, the maximal KINETIC energy is
calculated by adding half the escapement energy to the peak potential
energy (the other half of the escapement's energy contribution being
dissipated as the bob returns to a 0 angular displacement.) This changes
the value for Q but only slightly.
Similarly, the amplitude of this clock varies: today (friday) it is 47 mr
which has a much more distinct effect on the value of Q obtained.
Moreover, in the Cambridge vicinity, g runs 9.81
See http://www.bgs.ac.uk/products/geophysics/landGravity.html for N52.33
W0.0

None of this explains the large difference between your value and that
provided for Dr Hunt.
I notice that no estimation of the effect of suspension pivot rigidity in
space is given, other that a speculation about wind-driven deflection of
the tower.

Brian W
[I see that Doug S Drumheller - Sandia emeritus and Hugh Hunt at
Cambridge are both on your copy list. It would be interesting if they care
to contribute.]

On 5/14/2015 4:28 PM, Bernard Cleyet wrote:

/snip/ 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.
/snip/
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 find the running Q.
/snip/
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.)


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