Dynomometer log drop test

Eric Frei

Here's a short 2min video (9.7mb WMV) of a simple drop test which shows the forces generated.

I wont say too much, this was courtesy of the free Vermeer training day.

www.treeworld.info/video/6kgdroptest.wmv

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OsAGe85

Im going to 2 of those Vermeer seminars in Mid September, both for climbing. I cant freagin wait.

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Gotta love the smell 2 stroke and wood chips. Be smart, be safe.

Bruce Hopf

It's amazing how much force something that light can make as it falls. Would give you a good sized knot on the noggin if it fell on you, from that distance of a fall. Bruce.

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dov

Would give you a good sized DENT in the noggin if it fell on you. Mind you, that was the force of stopping it, not deflecting it, which may only take a smaller part of that force. Prob break your neck too.


Makes me think of replacing my ropes though...

Eric Frei

I have for some time pondered these figures.

And have done some research to discover some facts.

On this page there's a calculator and it also explains why these number can vary so greatly.

Energy of falling object

The issue is you can have the data of weight, distance, acceleration but the stopping distance is what blows the numbers out of the water.

we have weight = 6kg
Distance fallen = 1.4m
acceleration = 9.8m/s2

That derives an energy of 83.23 Joules at the end of it's journey but we cannot yet figure out the real impact force on the rope as we don't know the stopping distance. Different ropes will have different stopping distances plus the length of rope in the system will have varying amounts of stretch.

From the calculator on that link if the stopping distance was 0.1m it would generate roughly the equivalent of 80kg.

So if they used say 3 strand (more stretch) you would have got a lower reading. If there was more rope in the system same again. No doubt do this with say wire rope then the reading would be higher again.

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Bruce Hopf

Just imagine being hit from a falling tree branch, from the top of the tree. I think that your Council should realize, with some of the videos that you have posted here, how dangerous a tree can be, that is in sad shape.
I seen one of your earlier videos Ekka (I seen it this morning), that you had three trees together (I think they were some kind of pine) with the middle tree had a bunch of ant bores in it, and eventually the tree fell into the street, about 5or 6 months after you let the council know.
Council ignoring warnings, is an accident waiting to happen. I let our council know about a corner that is a mile and a half from where I sit. It has a Pear tree right on the corner, with branches sticking out, that you have to literally drive into the intersection, to see what is coming from behind the tree.
On the other side of the corner, there is two Ash trees, with the same thing. About 14 years ago, my Mother had an accident there at this corner. She couldn't see the car coming, and she was struck on the front right corner of the car, but still the moment of the car that hit her, pushed both cars out into a field.
I told the council that those trees were the main cause of the accident, because they caused a blind spot, that my Mother couldn't see past. They just looked at me as I was stupid or something.
Heck I seen so many accidents while driving transport trucks for over 13 or more years, and you learn after a while, how to see what had happened, or the cause of the accident.
Who was I to tell council about traffic accidents. I'm waiting to see another accident at this corner, than I'll step up to the plate, ans say I notified council about these trees that cause a blind spot, and see what happens then. I hope that it never happens, but never is a long time, that something could happen in that amount of time. Bruce.

__________________
McCulloch chain saws
1- Pro Mac 60, 1- Pro Mac 700, 2- Mac 10-10 Automatic's, 2- Mini Mac 30's, 2- Mac 110's,
2- Mini Mac 35's, 1- Mac 140 with Automatic Chain Sharpener,
1- Pro Mac 10-10, 1- Mac Cat, 2- Eager Beaver
2.0's, 1- Mac 1-10
Stihl chain saws
2- 044's, 2- 034's, 2- 024's, 1- 064, 1- 084,
Strunk chain saws
1- Busy Beaver, 1- SpeeDemon Special
Stand Back, I Have A Very Extreme Case of CAD (Chain Saw Addiction Disorder).

murphy4trees

Was that Scott Prophet... he's actually one of the more informative lecturers I've ever heard... BUT I despise his style... After about a minute of bidding for weight... I just wanted to say "SHUT YOUR MOUTH and drop the thing...

He called me somtheing like the "trouble maker in the second row when he spoke at the penn-del ISA conferecne a few years ago... His style got on my nerves and I had to give some lip back... I just couldn't stop myself...

Victor Lindsay

Was that a free class? How many CEU's? I never get free classes here.

Eric Frei

That class was free but the following ones you have to pay a notional amount like $25 or so.

Not sure about ISA CEU's.

They are informative and I think Vermeer/Sherril are doing a good thing because frankly with food and shirt give aways it cost them money. Sure they might sell some gear but how many gear sellers offer training style events from reputable sources?

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glennak

Not as much force as you think Bruce. Branches are dynamic (unlike blocks of wood) if they hit you the branches would keep moving as they bend. Called mass damping.
At the Australian Arbor camp a few camps back they cut the top off a tree and measured its load with a dynometer? It fell connected to a rope through a pully to a porta rap on another tree. So the force was absorbed by the bend in the tree loosing its top, the stretch in the rope but this was nothing compared with the flex in the branches when the log stopped. Everyone was expecting a shock load like the block of wood had, but it didn't have one at all just its weight nothing added.
Moral of story drop bigger heads and smaller blocks.

This mass damping affect can be felt if you remove all the branches from a tree and shake the trunk. Which is why you should leave as many branches as possible on a tree before you drop the head, unless you enjoy the ride.

Eric Frei

Excellent, pity we didn't have video of it.

What about if the top was held up and not allowed to run? I wonder what it would have read.

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glennak

It was not allowed to run at all except for bend in trunk and stretch in rope.

windthrown

The issue with falling (or moving) objects is simplified if you think of in terms of the integrated physics equasion: F = 1/2MV^2. This says that the Kinetic energy, or Force is equal to one half the mass times the velocity SQUARED. The mass is a constant, but the velocity is squared, so the energy gained is far more from the speed of the object rather than its size the faster it is moving. The speed increases from the acceleration of gravity the farther it falls. Potential energy is converted into kinetic energy, and more energy is gained by the falling limb, until at some point it reaches terminal velocity. That will not happen in the case of tree limbs falling though.

As for impact forces, we see that all the time on the ski patrol here. In the case of skiers, the dynamic is flipped. The trees and limbs are stationary, and it is the human that is falling and moving forward from the force of gravity (on skis). The impact energy from humans hitting trees can be brutal, and it turns into blunt trauma. We assess and send people down the hill all the time on backboard in ambulances with broken bones and concussions and all kinds of near fatal injuries. Some are pronounced dead on arrival. Three so far this year.