[ Follow Ups ] [ Post Followup ] [ TimeZone Public Forum ] [ FAQ ]
Posted by Bruno on September 13, 2000 at
07:19:03:
In Reply to: Defining some terms posted by Mike Bilow on
September 13, 2000 at 04:59:49:
Posted from Host: (195.101.81.54)
Partly right, but partly wrong. Deceleration occurs because of the application of force (this is Newton's Second Law of Motion), and pressure is by definition force per unit area. So the only way to decelerate something is to apply pressure to it.
>> I would rather say that to decelerate someting you must apply a force on it and a difference of pressure is a way of applaying a force.
: A watch rated to 10 ATM is rated for static pressure, meaning that it is slowly pressurized up to the rated pressure and just made to sit there for a while. Simple variations on this idea, such as pulsing the pressure up and down, can cause failures of seals. Indeed, this slight pressurizing and depressurizing cyclical pattern is what causes metal fatigue on aircraft. This is, interestingly, the same thing a watch experiences when worn by a swimmer.
>> I desagree on that point. The metal fatigue you are talking about is long term degradation of mechanical caracteristics of the material. To witness some fatigue effects on your watch, you would have to wait quite long.
: If a watch is suddenly subjected to high pressure nearly instantaneously, without
being brought up to that pressure gradually as it would be in a static test, then this has
as much a different effect as throwing the watch against the floor as distinct from gently
lowering it to the floor.
>> Nope. the trowing test is someting totaly different. By throwing it on the floor, you increase the force applyed by increasing the momentum of the watch itself, adding a load factor to its weight. As a side effect, you incrase the decelration. And there again, violent deceleration of some heavy parts mounted on thin axels (balance wheel) will ruin the movement.
If a watch is going 190 MPH when it hits the water, I seriously doubt that the seals are going to hold out. Exactly what part of the watch ruptures first may be hard to predict, but water resistance is very likely going to suffer.
>> you are here gessing on the abilty of the o-rings to react to instantaneous appliance of a moderated pressure (8ATM) ie force resulting from the difference of pressure between both sides of the o-ring. In 10ATM rated watches, o-rings are already constrained when mounted.