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I was just wondering how you guys, and girls work out the height of lower objects.Do you drop a rock and count or do you use a more accurate alti then say a altimaster.Also if you drop a rock and count, is there a basic formula you use to calculate the height.Or is it more like,the rock fell for 7 seconds, I'll delay for 3... or something! This is just something I have always been curious about. Thanks.

Many people use laser range finders. Usually accurate to +- 1 meter.

Ah, that makes sense!I thought it would be hard to work out 326 feet or whatever on something like my altimaster.No dropping rocks either eh?

Velocity = acceleration * time
Integrating you get distance = 1/2 acceleration * time^2.

Acceleration due to gravity is 32 feet/seconds^2 or 9.8 meters/seconds^2 so

Height = 16 feet * t^2 or 4.9 meters * t^2 with t expressed in seconds

This produces a result that's too high for taller objects because acceleration is not a constant - it decreases as velocity increases since drag goes up and acts opposite gravity.

The pull of gravity although is different in all places. For instance, here in Idaho it is 9.8 m/sec. I know it is not that different in most cases but it helps sometimes. Density of air is a factor too. $.02

gravitational force is not equal in all exits, correct. but there is NO way a jumper with ANY commercialy available equipment could tell the differences between the gravitation forces of different places.

and air friction is almost nill difference at altitude, especialy low jumps where its all about acceleration. and super especialy because that measurment method only works until air friction becomes a factor.

Here's the problem. Say you drop a rock. You dropped it vertically, right? If you lob it (maybe you have to clear some structure) enough to give it just a couple of extra inches above where you let it go, you'll add 1/10 second. Anyway, you record 3.3 seconds to impact. Maybe you're off by 1/10 of a second (if you're a ninja and you're using a stopwatch). If you went off of the sound of the rock hitting, you'll want to remember that sound will take 1/10 of a second to cover each 100 feet back to you. That can add up.

At 3.3 seconds, the rock is moving 105 ft/second. That means +/- 10 feet of error for every 1/10 of a second you're off. Altogether, maybe you're lucky and there's 2/10 of a second of error in your number. Is that significant? Could be if you were planning to freefall an object that you now know to be between 155 and 195 feet.

Laser rangefinders are cheap and give 1-yard accuracy. Rocks are even cheaper, but you probably shouldn't count on them to give better than 20 or 30 feet of accuracy even for a low jump. Rock drops only get worse from there.

Edit: Stupid typos...

i tell my friends to go first

Officially my favourite "first post" in a long time

THANK YOU

I use maggot, so far so good.

I've counted ladder rungs. dropped rocks. and my favorite, just said fuck it... what's the worst that could happen. that ended up w/me jumping into a vally with monster boulders for a LZ and walls nearly too steep to climb out of. So I took the bridal off and rolled it over for a second one.... it's a wonder any of us are still alive

 

On the subject of range finders...Are you able to instanly calculate the top height of any object you point it at? or is it a case of working out a distance away from it when stood at 45 degrees to the top?

the laser measures distance, not height. I have done calculations of angle/distance shit, but i failed college algebra twice, so i try to get to the base of the object.

funny, i can do all the seemingly more complex math for Frasca, but i cant get college algebra down. oh well. anyone know where i can buy a degree? not kidding.

The range finder gives you the distance from where it's at to the object it's pointing at. If you are som distance from the base of the object you will need to use the pathagorean theorem to calculate the actual height.

www.algebra.com/calculators/geometry/pythagorean.mpl

When I get my two Bachelor's done, you can buy one of my Associates from me.... They aren't worth a damn anyways. I had to go back to school because I couldn't find a job with them.

Algebra really isn't that hard. Try differential calculus. Now that class sucked!

how about this u have 60 jumpe the only thing u should be thinking about is getting your c- license silluy rabbit base is n ot for kids

i need a bachelor

u mean a bacheler party with lots of hookers yah thats a great idea

I like hookers..... prostitutes charge too much!