Physics Question: Basal vs Canopy Anchor Forces

[Shadowscape]

No one is saying the pull force changes. What changes is the amount of force on the tree as well as the direction of force.

The direction of the pull line force does not change. It can't. It has to follow the rope. The amount of the pull line force also does not change. 150 lbs is 150 lbs. An additional force is introduced, the vector force. But that does not alter any of the two above. It is just acting upon the crotch, which really would slightly help pull the tree in the correct direction, although you probably would not experience any notable difference.

 

[Shadowscape]

I give up. You fellows can try and wiggle your vector force into the equation all you want. Go for it.

 

[Muggs]

This is starting to seem like a semantic issue. To me, the question being asked is: in order to accomplish the exact same task (pulling the tree over), will I have to pull harder if the rope is anchored up top, or if it's anchored at the base. Or does it even make a difference?

Is that the question @Maplegeddon213 , or is it something else?

My answer to that particular question, based on my experience, is that it doesn't make enough of a difference to worry about it.

That being said, are they actually both *technically the same thing? No, they're not. Is the difference worth getting into an argument over? Well, Treebuzz is a great place for an argument among friends

 

[southsoundtree]

Quite often, addressing a person by name adds clarity. Restating their point, before responding to it, and being explicit in explanations, including drawings, helps a lot!!

Sometimes, even 'knowing' everyone in the conversation, it can be hard to track.

 

[evo]

This is a fun one. I see both arguments but I disagree with the force vector theory.
In both base tied and trunk tied pulling the stem is acting as the fall of the rope. One is dead ended. So the force vector is there but identical

The only variable difference is the base tie, if your using amsteel, no difference, but if nylon there is more rope in the system. More pull force needs to be applied to overcome the stretch in the line.

No practical differences other than rope length, and security. (We base tie pull lines all the time in conifers)

The huge player with this is leverage and foot pounds.

 

[Tuebor]

No I do not. The 150 lb pull from the winch is acting directly in line with the rope. All of it. That is the only line it can travel. The vector force is acting between the tree and the winch, but that is not the pull line force. You can't transfer force through thin air.
There is a combination of pull line force on the rope from the winch (in a straight line from the winch to the tree), and a relatively equivalent force on the basal anchor line going off at an angle. Combine those two forces together and a portion of that combination is acting as a vector force. But the pull line force is still in a straight line from the winch to the tree. The ROPE is being pulled, not some space some SPACE at another location. It is not physically possible to transfer a mechanical force through a space time warp whatever is being imagined here.
The result of this straight line 150 lb pull is creating another vector force, but it is not taking anything away from the 150 lb straight line pull.

The base of the tree is pulling 150 lbs the opposite way - that's why you don't fall on your back. The fork in the tree is experiencing the combination of those two forces. It experiences them as a higher force in a direction that bisects the rope angle at the fork. The horizontal component of that force is what is being applied to "push" the tree over.

I'm only getting into this because the poster included the word "physics" in the thread title. It probably is indistinguishable considering all the other factors: friction, rope stretch, stance ergonomics, footing, leans, etc

 

[southsoundtree]

This is a fun one. I see both arguments but I disagree with the force vector theory.
In both base tied and trunk tied pulling the stem is acting as the fall of the rope. One is dead ended. So the force vector is there but identical

The only variable difference is the base tie, if your using amsteel, no difference, but if nylon there is more rope in the system. More pull force needs to be applied to overcome the stretch in the line.

No practical differences other than rope length, and security. (We base tie pull lines all the time in conifers)

The huge player with this is leverage and foot pounds.

You have to pull more rope to remove the stretch, but not with more force.

 

[Bart_]

I see descriptions of forces developed in the WOOD of the tree and you can imagine all the weird possible forces and torques developed in my bad professor example. They would be correct.

A first year engineering free body diagram could have planes/places drawn in various chosen locations to solve the interaction forces. The OP's original question plane is somewhere along the rope between the crotch and the winch cutting through the rope. That's Shadowscape's dead on analysis. Another plane is at the hinge. In that case the added force is pull x sine(angle) additionally downward and pull x cos(angle) sideways. If you want to get picky if the crotch is at the side or back of the trunk the pull rope is slightly twisting the trunk too by tension x diameter/2x a trig function if you pick a concentric axis for analysis. If you pre-tension before the cut there's CofG backlean torque let's say referenced to the hinge (could be zero if straight tree) and bending beam torque of the trunk tweaking slightly by the rope tension. It varies with location you reference the analysi to, with max bending torque a the root plate or more practically at the hinge. But these are all internal localized stresses, not the OP's question about pulling the tree over with a given pull rope force. The answer is you can create a variety of internal forces depending how you configure but given the same height up the trunk attachment point and the same winch pull force it will pull over the net or whole tree the same. For practical purposes the second analysis item of interest is the torque in the fall/pull direction developed by the winch rope. That's the basis for Muggs' optimum pull rope angle question.

I think I'd win for the most needlessly confusing bad professor's configuration that has the same net pull over gumption. But it proves the point.

 

[evo]

You have to pull more rope to remove the stretch, but not with more force.

I don’t think this is the case.
If one pulls 100’ with 100lbs on 3% rope, and then one pulls the same but 300’ much of the applied load is just taking the stretch out of the line and less on the anchor. As the energy applied is absorbed by rope stretch.
Think of speed lining on a super static rope vs nylon core. One certainly feels the difference for better or worse.
Yarding is much the same, one has to take the stretch out of the line before the piece moves, with a static line it’s there at the load instantly.

 

[DSMc]

To be a stickler, ropes don't break hinges in almost all cases...

It was a descriptive term not meant to be taken literally.

 

[DSMc]

... just like when climbing SRT on a base anchor, my 150 lb body will produce a 300 lb force at the crotch (neglecting friction, stretch, yada yada...)...

Right on cue: let's talk about the science involved while at the same time simply disregarding key components.

 

[Tuebor]

Right on cue: let's talk about the science involved while at the same time simply disregarding key components.

It's a matter of principles: details can come later. No need to determine whether the force is 151.667 lbs or 148.207 lbs.

 

[Maplegeddon213]

 That

This is starting to seem like a semantic issue. To me, the question being asked is: in order to accomplish the exact same task (pulling the tree over), will I have to pull harder if the rope is anchored up top, or if it's anchored at the base. Or does it even make a difference?

Is that the question @Maplegeddon213 , or is it something else?

My answer to that particular question, based on my experience, is that it doesn't make enough of a difference to worry about it.

That being said, are they actually both *technically the same thing? No, they're not. Is the difference worth getting into an argument over? Well, Treebuzz is a great place for an argument among friends

That was my original question and it has been answered: it's not a significant difference on the intended outcome between either method. Thank you everyone again for the input and helpful diagrams

I love arguing semantics, so this thread hasn't been frustrating or disappointing to me.

 

[southsoundtree]

It was a descriptive term not meant to be taken literally.

I know.

Generally, I want people to recognize that bending the hinge takes a lot of force. Gravity often supplies a lot of that force.

I don’t think this is the case.
If one pulls 100’ with 100lbs on 3% rope, and then one pulls the same but 300’ much of the applied load is just taking the stretch out of the line and less on the anchor. As the energy applied is absorbed by rope stretch.
Think of speed lining on a super static rope vs nylon core. One certainly feels the difference for better or worse.
Yarding is much the same, one has to take the stretch out of the line before the piece moves, with a static line it’s there at the load instantly.

You definitely have to take in more feet of line to get to the point of being able to apply 100#.

As the stretch is removed, there is more resistance building. At first, you will not have 100# of resistance to be able to apply 100# of force.

 

[TheTreeSpyder]

To me, the over the top lacing usability performs better:
>>doesn't just test, but braces the top
>>thus can flex top more sometimes with more confidence>>which is more input pull
>>would seem to give more of a rolling input to a rolling output, especially to backlean
>>easier untie after down, and by sawyer, at easiest point, with knot on top, not buried>>gingerly pull out with truck
.
Seek to force stronger hinge, by exercising it at birth
>>pulls after committed only scurry, do not strengthen
>>cuts after committed weaken to faster, may free some to control direction
Speed is the cSQUARED part of e=mcSquared
>>prefer clean, committed, slower for less ground concussion type of art form
Prefer not serving directly into harshest pull of lean
>>but to lesser focused side of lean some
>>to practice
>>and move slower/softer(in good wood)
Employ speed specifically if need to punch thru something
>>or slam hard to Dutch face for greatest response back
The patterns are all cosine.
.
Doc Shigo lent that a hard pounding rain could disrupt the sea of soil mycors
>>so what of slamming tree and all kinds of trucks compression this sea?

 

[ghostice]

Crosspost to another discussion? Terry Hale's video does a great job of explaining the vector forces involved in yankin a tree and the bending moments at the hinge etc from an engineer's point of view. Maybe worth a look here too. Cheers.

 

[Bart_]

Terry Hale has genuine stress strain analysis and goes into fiber crush mode failure and tensile failure - at the hinge. Highly recommend watching. Cut him a break as a wanna be arborist.

Tuebor, the principle of a 2:1tension ratio over rough bark makes 200 lbs 200lbs = 400 lbs become 200 lbs 100 lbs = 300 lbs. Too big to be brushed off as a detail. Worth consideration IMO

 

[ghostice]

Terry Hale has genuine stress strain analysis and goes into fiber crush mode failure and tensile failure - at the hinge. Highly recommend watching. Cut him a break as a wanna be arborist.

Terry I think woulda been great to work with in projects - he’s actually an engineer that has the knack of explaining technical detail. Not everyone has that for sure. Cheers

Addenda after pondering with single malt: nothin' to do with vectors an such but come to think of it, I kinda do usually go for a cinch way up if I can, rather than a basal tie - just lowers the amount of rope I'm yanking on in "the system" and thus lowers the amount or stretch I have to take out before getting anywhere maybe. Just a thought, no great revelation I know. Cheers.

 

[TheTreeSpyder]

It is truly, truly a wonder, how can pareto/'pare to'(link) the same vital few pivotals, that blossom to so many outcomes that we chase on outer layer
>>going instead to other end of the pivotals not outcomes
>>can sometimes eliminate chase
>>as it is all there>>pivotals with input/output arms too !
And still a tricky thing of endless possibilities as adjust the 'vital few'(way beyond 80/20 hear tho) 'volume' knobs of angles in, out, force, rigidity, velocity etc. Math is the language of functional logic, a scenario decoder to pull back curtain, and see wizardry is simpler than thought, under the hood. If can catch and sift out the consistent patterns, it is easier to see them in other things upfront, like xRay vision not blinded by the chrome and wax skinned over of the real deal of what this ride can do!
.
On forward hitchpoint of trunk column support, or motion to
>>from vector dimension legs of horiz and vert SEPARATE dimensionals of either or, as to encompass all
>>both quantities can be usable to bring beast down i think.
>>depending on dis-position of tree geometry employed.
How the 'hybrid' output of operations vector inheriting some % from each purebred extreme parent horiz/vert (displacing to the exclusion of the other parent dimension to encompass all possibilities between) 'expresses' hybrid's own mix of potentials then to the scenario.
Both dimensions in non-linear position, in rigids/tree
>>can assert leverage per reveal force x position from pivot axis
>>just as horiz
>>this can really complicate backlean pull ..
.
And with that model now are in radial rotation around hinge pivot as output>> not a linear motion.
pull point forward of column scenario>>without support column under/@BDC, the downwards vertical force can help pull beast down too
>>and the pull forward horiz pull across
>>both at play for the rotation, as need countering, but unaligned parts of each to the rotation total
>>for linear alignment of trunk as column to pull direction gives no rotation from vert axis under TDC to column/vertical
So down can help per dis-position of the spar as a column or lever to force considered, and then points between of some of each parent extreme to the now hybrid position between 0-90 purebred parental dimensional extremes.
>>just as across portion of pull can help until it has aligned linear sweetspot of Zer0 rotation, no sin(e) extending from benchmark axis cos of tree architecture leveraging; then is pure linear force, not rotational.
>>jest the tilting of a few (underlying)rules back and forth to all these outcomes..
.
will stop 'pre-Zen'tation there this time...
.
"Education is that which remains when one has forgotten everything he learned in school." -Einstein
for then came trees yo...

 

[Dan Thornton]

For those who are still tempted to think that the rope going down from the natural crotch to the basal tie on the tree is contributing to the perpendicular pulling force, thus aiding the falling of the tree, try out this thought experiment for size ...

Let's reverse the forces. Instead of pulling 150# on the pulling rope, which happens to also place a load of maybe 80# down to the base of the tree, let's set the whole thing up backwards.

Tie the rope at an anchor a sufficient distance from the tree.
Instead of having the rope go over a natural crotch, run it through a port-a-wrap up in the tree where the crotch should be.
Then place a GRCS at the base of the tree (above the felling cut of course, which no one would ever do, since the fall would probably ruin the GRCS, but it's a thought experiment, so give me a break!).
The GRCS is pulling a rope that is running through a Porta-Wrap then from the portawrap outward to the anchor.
The goal is to put 150# of pressure on the rope between the porty and the anchor.
Assume that the 1 and 1/2 wraps on the porty steal all but 10% of the pull to friction.
The GRCS would need to pull 1500# on the rope to produce 150# of tension on the rope going to the anchor.

Here's the point --- there is still only 150# of pull on the tree toward the anchor, regardless how much pull is on the rope going down parallel to the tree.