NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/space/18306

Text File | 1992-12-28 | 4.8 KB | 105 lines

Newsgroups: sci.space
Path: sparky!uunet!wupost!eclnews!wucs1!gene
From: [e-mail] (_Floor_)
Subject: Re: Acceleration
Message-ID: <[e-mail]>
Sender: [e-mail] (News Administrator)
Nntp-Posting-Host: wucs1
Organization: The K-Zoo Crew
References: <[e-mail]> <[e-mail]> <[e-mail]>
Distribution: sci
Date: Mon, 28 Dec 1992 18:10:24 GMT
Lines: 91

In article <[e-mail]> [e-mail] (Pat) writes:
] Certainly electronics can be built to be flexible,  it's just what degree
] of flexibilty you desire.  Flex is a stress/strain relationship.
] Steel is flexible, rubber is rigid.  you just need to define these terms
] first.  besides, if you build with amorphous materials,  you can get
] quite a flex out of silicons.

And retain precisely the same semiconducting properties? Anyhow, I was
thinking more along the lines of welds and other connections. Stresses
would occur in bending electronic boards - everything would have to
be completely secured.

] and i believe the designers understnad the material characteristics
] of their probes quite well.

I expect so too. It isn't that I disbelieve they'll do this, but that
I find it astounding they could achieve such durability.

] >] But other than that, and factors such as prolonged stress on human hydraulic
] >] systems, the greater problem can be with rapid changes in acceleration, which
] >] are of course associated with short bursts of acceleration. (I believe the
] >] usual term for the time derivative of acceleration is "jerk".) These rapid
]
] Actually,  i think the term is Impulse.

No, impulse is equal to the change in momentum, which is equal to force*time.

] >You're joking me if you think the Galileo probe will experience constant
] >deceleration. There's going to be buffeting worse than we could imagine,
] >I imagine (:-). Especially at speeds many times that of sound (which I'm
] >sure will be different for the Jovian atmosphere)! So you're point is
] >very applicable. Experiencing this jolting for milliseconds (as per
] >a dropping watch) may not cause any damage. But if you dangled the watch
] >from the ceiling and proceeded to place a jackhammer at its face,
] >slamming into its face for a couple of minutes, liklihood is that
] >the watch will no longer function! Ditto for an atmospheric probe.
] >That thing is going to get one whale of a beating. You've helped me
] >emphasize my point even more! Thanks :-)
]
] Hopefully this kid will take a physics class.
]
] I think he is mistaking  Work with Force and energy.
]
] Work is force through a distance,  Energy is work*time, Force is mass*Accel
] ( boy i hope i got these right :-) )

Gee, thanks for the diminutive attitude towards me :-). Sorry, energy is
not work*time. Energy applied is _equal_ to the work. Energy and work,
however, are power*time.

] It takes energy to achieve a momentum change.

Sure, OK.

] A probe has high momentum hitting atmosphere.  it gets  a high acceleration,
] on a small mass.  not a lot of force,  exerted through several miles of
] atmosphere,  for a few minutes.

Small force? I think they said the probe would feel an acceleration of 350 g's.
It's receiving a force 350 times that of Earth's gravity at the surface of
the Earth. That's quite a bit of force if you ask most people.

] I think the kid is missing the fact that while the accelerations of dropping
] a watch and hitting it with a sledge are the same, the work products are significantly  different.

Huh? Me litle kid not udnersnad wy if force and disstence same, work difrent.
And _significantly_ at that!

] Try this.   drop a timex.  work out the acceleration.
]
] Now,  hang the timex from a string.   Let a pendular mass strike it, at low spe
] ed.  work out the acceleration.  keep increasing the mass and speed.
] continue until the timex dies.   I suspect you will be surprised at how
] high you can go.
]
] Halting a 5 lb sledge witha watch is a major momentum change, hence mucho
] work in a millisecond.
]
] Conducting momentum transfer via pendular masses, is much less work.
] you can simulate this with that desk toy, using  pendular ball.
] tape a timex on to one of the balls.  it should survive.

He he ha ha! What a joyous laugh you've given me this morning! This just
isn't the truth. Have a pleasant day! :-)

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