Re: Jurassic Park

[dg04@ns1.cc.lehigh.edu (DAVID GRUMBINE)]

>>Ok, let me ask this - if you had a high voltage fence and you took a
>>stick and threw it at the fence - would it zap the stick?  Also, if
>>the stick were wet would it do this?

Well, ever look at high voltage lines and wonder why birds keep sitting on
them if they are getting fried?  Because they're not getting fried.  So
unless there's a potential difference between the wires (which the shorts
should eliminate) a wet or dry stick won't get zapped, nor will a Timmy.

>Another good question I thought about when watching the movie!
>It's kind of a moot point in regards to the fence in the movie
>since that was obviously not an electric fence design.

I'd have to agree with that!

>I have seen real electric fences for cattle near here. They consist
>of wooden posts with wires running along them (no cross wires,
>though!). One of the wires running along carries the high
>voltage. The voltage is applied in short pulses to save cost
>and enhance the effect!

Actually, it's more to save the power supply.  An electric fence has almost
no resistance (just plain conductors) so keeping the power supply on for
any length of time would either fry the supply or melt all the wire in the
fence.

>I remember the stick in the movie looked quite dry (although I
>guess that was a high-humidity environment). On the cattle
>fence the stick would have to be moist and touch the high-voltage
>wire *and* ground simultaneously in order to get zapped. But with

With real high voltages (10kV isn't really THAT high) being wet or dry
wouldn't make any difference.

>the short pulse-length they use, the zap would not be visible.

Ahh, no.  Ever get shocked by normal house current?  Those pulses are only
1/60 second.  Pretty short.  But you can see spark if you short it out!
Mighty big spark too, I can add from experiance!

>[....]
>I guess you have to be like a kid and suspend disbelief
>in order to really enjoy some movies.

Oh well.  Good movie anyway, even with these little oversights.  :-)

-dave
-- 

=============================================================================
The oppinions expressed above may or may not be my own.  But I'm not telling.

Physics is fun! ....  Honest.
=============================================================================
Dave Grumbine, Jr.       dg04@Lehigh.EDU