Hey rad,whats a radian

kyle · Post by **kyle** » Thu Feb 19, 2009 5:03 pm

Lucifer wrote:There's probably enough variance across the surface of the earth to make 9.81066 too much precision.

It was online homework through university of taxes, I'm assuming that is pretty precise where they are located.

subby · Post by **subby** » Fri Feb 20, 2009 1:20 am

G'Day guys LTNS

In Melbourne, Oz, g is actually 9.800 m/s^2.... so it's pretty easy for me

radian · Post by **radian** » Sun Feb 22, 2009 5:38 am

98/9.80/9.81/9.82 . . hmm..well..lets hope .texas..sweden..canada..and melbourne..dont collaborate on the next space shuttle. .there will be bumps and lumps all over it..doors falling off..coffee machine wont deliver the cup properly....poor astronauts will have to resort to drinking their own urine..oh wait .i think they already do

kyle · Post by **kyle** » Sun Feb 22, 2009 8:17 pm

radian wrote:poor astronauts will have to resort to drinking their own urine..oh wait .i think they already do

not till July

they would use big G instead of little g

Communist · Post by **Communist** » Sun Mar 01, 2009 2:59 am

[/lurk]

Well, well... someone popped the question while I was bored on a lazy weekend, so I figured I'd weigh in. (Plus a friendly greeting to some old-timers I haven't seen in ages

.)

If you were serious about using an accurate value of little g and for what ever reason don't trust anything in the literature, you can conduct your own experiment. It's a nontrivial undertaking. For educational purposes you can measure it with some photogates or even a stopwatch, but don't count on getting anything accurate there.

Alternatively, you could try to use the Earth Gravitational Model which models the equipotential surface of the earth with some really long polynomials (order 360 in the 1996 model, I think they released a new version with more than 2000 terms). I won't claim to understand how to go about doing this.

If you want something you can reasonably figure out by hand, I'd recommend the WGS84 report. This is an accepted standard for use in many organizations, including the US Dept. of Defense. The equations to calculate g (or rather, gamma-sub-h in their notation) can be found on pp. 42-43 of the PDF. You will need to input your geodetic coordinates (latitude, longitude, and height above ellipsoid); the other constants can be found elsewhere in the report.

And yes, kyle is right, in space the value of little g would be rather useless, since it's really only valid on the surface of the earth.

Oh, and subby is the physics nut here, I wouldn't be surprised if he signed back in just to whack me for all that misinformation.

Now, back to my cave...

radian · Post by **radian** » Mon Mar 09, 2009 2:47 am

thanks for the links--
shame the vernier link is broke---
absolutly facinating..i guess the 30 gravitational anomilies relate to denser substances and different altitudes
and the only constant for astronauts would be --light

Post by **Lucifer** » Mon Mar 09, 2009 10:31 pm

Hey communist, long time no see, eh?

I work in a physics lab these days, and we have all sorts of Vernier crap. And it is that, crap, unless you're working in an educational environment, in which case it's a-ok.

We typically measure little g as 9.79. I haven't seen anybody get higher than that that didn't have a clear error in their procedure.