Author Topic: $hit Happened Sometimes  (Read 13174 times)

Offline chrisyen

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Re: $hit Happened Sometimes
« Reply #25 on: November 08, 2012, 04:45:25 PM »
Don't think crystal costly...
Few hundred bucks shd b able to cure!!!

Movement not affected right? Running?

Offline ck77

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Re: $hit Happened Sometimes
« Reply #26 on: November 09, 2012, 07:24:36 AM »
Not sure the extent of the damage, he has yet to send it to service center.
Have advised him to pull put the crown to stop the movement.

Offline jacky8888

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Re: $hit Happened Sometimes
« Reply #27 on: November 09, 2012, 08:13:52 AM »
but with the day date misaligned....
i dont think its a easy task to rectify it.... :P
Jacky Wong

Offline jason_loh

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Re: $hit Happened Sometimes
« Reply #28 on: November 10, 2012, 05:22:08 PM »
Aiyoh! Anyway good excuse to upgrade  ;)

Offline Kennypane

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Re: $hit Happened Sometimes
« Reply #29 on: November 11, 2012, 11:51:17 AM »
Someone should start a thread on physical damage to your watches. Fall, stepped, cooked, frozen, burnt, thrown, abused, knocked, etc.

Offline ashwin1987

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Re: $hit Happened Sometimes
« Reply #30 on: November 11, 2012, 04:50:34 PM »
My marina militate, one day old fell from my hands face down, and it was gone.... Sigh... So ordered again.  :thumbsup:

Offline terrenceterrence

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Re: $hit Happened Sometimes
« Reply #31 on: November 11, 2012, 06:36:40 PM »
Not sure about the time but 7750 does not have quickset date and day ifi remember correctly. So might just be in the midst of date-day change.

but with the day date misaligned....
i dont think its a easy task to rectify it.... :P
Better outrun my gun....faster than my bullet


Offline Jeffrey8891

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Re: $hit Happened Sometimes
« Reply #32 on: December 18, 2012, 09:07:49 AM »


Let's do some simple physics (my first attempt after 23 years)......

Assuming the watch weighs 200g or 0.2kg

Force = mass x acceleration
F= 0.2kg x 10m/s2
F= 2N

The watch fell on its face. I assume the diameter of the dial / crystal is 40mm. Hence the radius is 20mm or 0.02m. Area of the dial / crystal is therefore approx 3.1416 x 0.02m x 0.02m = 0.001256 metre squared.

Pressure exerted ==> P = F/A = 2/0.001256 = 1,592.3 Pascal = 1.5923kPa.

Now, from my memory, 1 ATM is 101.3kPa.

Can 1% of the atmosphereic pressure really crack the crystal like that? Or maybe my physics is rusty beyond help?  :laugh:

I think it is related to impulse force it endure rather than the force it has during its fall. Your calculation is based on during its free fall where the acceleration is the gravity. However, when it hits the group, there is a change in momentum.

Take 1m height, acceleration = 9.81 m^2 / sec and initial velocity = 0 m/s
By using one of the kinematics equation, v^2 - u^2 = 2as

v^2 - 0 = 2(9.81)(1)
v = 4.429 m/s at the last moment before impact.

momentum, p =mv = 0.2kg x 4.429m/s
                         =0.8859 N s

during impact, the watch was stopped almost instantaneously because there wasn't anything slowly it down and for the sake of calculation,
lets say that the impulse time is 1 x 10^-7 s (that is still not exact 0)

0.8859 N s / 0.0000001 s

Then the impulse force would be 8859000N !

let say the WR is 30 bar = 30 x 101.3x10^3 = 3039000 Pa

it means the watch can withstand force of
 F = P x A = 303900 Pa x 0.001256 = 3816.984 N

So now you see the logic. If it lands on the carpet, it has more time of slowing done, to let says 0.5s , then the impulse force would be reduced to 1.7718N

Cheers  :Cheers:

Offline sshark

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Re: $hit Happened Sometimes
« Reply #33 on: December 18, 2012, 09:13:42 AM »
Didn't know we have so many engineers and scientists on board :)

Offline Jeffrey8891

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Re: $hit Happened Sometimes
« Reply #34 on: December 18, 2012, 09:24:08 AM »
Didn't know we have so many engineers and scientists on board :)

i'm still student !  :D

Offline Enkidu

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Re: $hit Happened Sometimes
« Reply #35 on: December 18, 2012, 11:38:35 AM »
Didn't know we have so many engineers and scientists on board :)

i'm still student !  :D

You are right Jeffrey!!! My calculation was flawed in that it only dealt with the force / pressure when the watch is say, resting on a surface, not the impact itself. Yes, it's the change in  momentum or more precisely the rate of change of momentum =>

Rate of change = (mv-mu)/t
= m(v-u)/t
=ma
 which is the applicable force!!!!

2013 Nobel prize in Physics jointly awarded to you and dpkong. :laugh: :laugh: :laugh: :thumbsup: :thumbsup:

Offline STT1987

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Re: $hit Happened Sometimes
« Reply #36 on: December 18, 2012, 02:27:17 PM »
There is no way that the impulse time is 1x10^-7 s which is a microsecond. Not unless the watch is falling down at near the speed of light and rebounds at nearly the same speed.

Quote
http://www.atomicarchive.com/Fission/Fission8.shtml
The complete process of a (nuclear) bomb explosion is about 80 times this number, or about a microsecond.

The original estimates is okay. No need to bring in impulse time unless you know for sure the watch rebounded. Also, the pressure rating means nothing when you discuss things like these, since basically pressure rating only takes into account water tightness (rubber seals, screw integrity etc.)
“Do not argue with an idiot they drag you down to their level and beat you with experience.” - Mark Twain
This video will prepare you for internet life.

Offline dpkong

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Re: $hit Happened Sometimes
« Reply #37 on: December 18, 2012, 04:56:11 PM »
Didn't know we have so many engineers and scientists on board :)

i'm still student !  :D

You are right Jeffrey!!! My calculation was flawed in that it only dealt with the force / pressure when the watch is say, resting on a surface, not the impact itself. Yes, it's the change in  momentum or more precisely the rate of change of momentum =>

Rate of change = (mv-mu)/t
= m(v-u)/t
=ma
 which is the applicable force!!!!

2013 Nobel prize in Physics jointly awarded to you and dpkong. :laugh: :laugh: :laugh: :thumbsup: :thumbsup:


Can some engineer kindly convert that to it's equivalent in beer and pasta??

 :Laughing_on_floor:

Offline bcard

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Re: $hit Happened Sometimes
« Reply #38 on: December 19, 2012, 10:00:33 AM »
 :o

Offline Jeffrey8891

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Re: $hit Happened Sometimes
« Reply #39 on: December 20, 2012, 11:20:36 AM »
There is no way that the impulse time is 1x10^-7 s which is a microsecond. Not unless the watch is falling down at near the speed of light and rebounds at nearly the same speed.

Quote
http://www.atomicarchive.com/Fission/Fission8.shtml
The complete process of a (nuclear) bomb explosion is about 80 times this number, or about a microsecond.

The original estimates is okay. No need to bring in impulse time unless you know for sure the watch rebounded. Also, the pressure rating means nothing when you discuss things like these, since basically pressure rating only takes into account water tightness (rubber seals, screw integrity etc.)

the impulse time is the time taken for the watch to change its momentum, it doesn't have anything to do with how fast the thing is falling, regardless the watch is travelling about the speed or light or as low as 1m/s , when it hits the floor, it still stops almost instantly. However, i do agree with you on the pressure rating but i use that as a reference only.  :thumbsup:

Offline sshark

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Re: $hit Happened Sometimes
« Reply #40 on: December 20, 2012, 02:57:32 PM »
1 microsecond is 10-6 of a second. And as we get closer to the speed of light i.e 0.8c Newtonian physics fail and the world will behave as what was described by Einstein.

There is no way that the impulse time is 1x10^-7 s which is a microsecond. Not unless the watch is falling down at near the speed of light and rebounds at nearly the same speed.

Quote
http://www.atomicarchive.com/Fission/Fission8.shtml
The complete process of a (nuclear) bomb explosion is about 80 times this number, or about a microsecond.

The original estimates is okay. No need to bring in impulse time unless you know for sure the watch rebounded. Also, the pressure rating means nothing when you discuss things like these, since basically pressure rating only takes into account water tightness (rubber seals, screw integrity etc.)

the impulse time is the time taken for the watch to change its momentum, it doesn't have anything to do with how fast the thing is falling, regardless the watch is travelling about the speed or light or as low as 1m/s , when it hits the floor, it still stops almost instantly. However, i do agree with you on the pressure rating but i use that as a reference only.  :thumbsup:

Offline Jeffrey8891

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Re: $hit Happened Sometimes
« Reply #41 on: December 21, 2012, 06:55:34 AM »
1 microsecond is 10-6 of a second. And as we get closer to the speed of light i.e 0.8c Newtonian physics fail and the world will behave as what was described by Einstein.


yes , true but that is not the speed of light, it is the time taken for the watch to decelerate. Its unit is not m/s . It never travels close to that fast. But it decelerated that fast, which has a unit of m/s2 .

Offline kenixck

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Re: $hit Happened Sometimes
« Reply #42 on: December 21, 2012, 09:33:15 AM »

all wrong, the floor was this