keithl@tekcad.UUCP (Keith Lofstrom) (10/02/83)
As much as I enjoy interminable political debates in net.physics, I will
interrupt with a relatively value-free thought problem. This thought
problem requires:
A weight scale with "infinite sensitivity", no memory, and no platform
deflection.
An hourglass with "infinitesimal" sand inside.
Set the hourglass on the scale with the sand in the upper chamber.
What does the scale read as a function of time? How will the changing
behavior of the stream of sand change the apparent weight?
To start with, let's leave Heisenberg, Einstein, and Boltzmann out of this
(No quantum, relativistic, or thermal effects) so more folks can play.
What do YOU think happens?
Physically yours;
--
Keith Lofstrom
uucp: {ucbvax,decvax,chico,pur-ee,cbosg,ihnss}!teklabs!tekcad!keithl
CSnet: keithl@tek
ARPAnet:keithl.tek@rand-relayjames@umcp-cs.UUCP (10/04/83)
(Let us also have no friction, and no air inside the hourglass.) Then, at any time, all mass in motion represents some kinetic energy, which therefore must not contribute to the potential energy in the compressed scale. So the scale reading is effectively a function of how much mass is in motion (and at what velocity.) If we assume that, between start and end, a constant amount of sand is always falling at certain velocities, then the scale reading is constant, but less than the 'real weight' of the hourglass+sand. However, depending on the shape of the hourglass, the motion of the sand which is slowly shifting down towards the hole will vary with the amount of sand left in the upper half of the hourglass, thus complicating everything. Now can we invoke Einstein, Heisenberg, and Boltzmann? --Jim O'Toole
kevin@ecsvax.UUCP (10/04/83)
The following Thought Experiment was proposed by Keith Lofstrom (tekcad.62): > A weight scale with "infinite sensitivity", no memory, and no platform > deflection. > An hourglass with "infinitesimal" sand inside. > > Set the hourglass on the scale with the sand in the upper chamber. > What does the scale read as a function of time? How will the changing > behavior of the stream of sand change the apparent weight? As for the first question, the weight will increase with as a function of time. The increase is justified by the fact that objects at higher altitudes weight less then objects a low elevations. The change may be small but then the scale is "infinitely sensitive." The second part of the question I think was answered by Lew Mammel, Jr. (ihuxr.679). In his article he stated, that the falling mass would exert a small force on the bottom of the Hourglass.
Shinbrot.WBST@PARC-MAXC.ARPA (10/06/83)
Keith, The question is akin to the one concerning a 190 lb. man carrying three 5 lb balls across a bridge which can only hold 200 lbs. Can he cross by juggling them, keeping one in the air at all times? - Troy PS. No.