- Location
- Massachusetts
The biggest problem in calculating the forces lies in the unknown variables. We can find the formulas (such as f=ma, v^2 = v^1 + at, Ft = mv^2 - mv^1, etc.), but it is measuring distances that is problematic.
The formulas will tell you how much kinetic energy a particular piece of falling wood has gained when it reaches a particular point in it's fall. That's great to know, but you can only determine the force imparted to the rigging system (or driveway, or whatever else it impacts) by first determining the distance over which the acceleration (from fast to stop; some call this deceleration, but it's properly referred to as acceleration and may be shown as a negative value) occurs.
We know if the object lands on the driveway on a cold winter day, it will accelerate quite rapidly. We also know that if the object is "caught" on a dynamic line, which is tied to a leaning tree which bends under the force, and is controlled by an experienced groundie who will let the load run, the acceleration will occur over a greater distance and therefore the force will be minimal over the duration of the acceleration.
So, the rules of thumb may be our best shot. Also, using a dynamometer is a great idea because it gives you the true reading without running through the calculations. Obviously, you can't use the meter everytime (besides, when you rig the piece that was a bit too heavy, it will be too late to check the meter) and we can't do demonstrations with every imaginable piece of wood.
Do control the variables you can: Keep your block and hitch as close as possible when blocking down; teach the groundies how to let the line run effectively.
On that note, how do some of you "let it run" when dropping a piece down onto a speed line?
By the way Glens, I do not intend to slow your progress towards finding the formulas; I spent a while searching my self. If you find something good, I'd love to see it.
The formulas will tell you how much kinetic energy a particular piece of falling wood has gained when it reaches a particular point in it's fall. That's great to know, but you can only determine the force imparted to the rigging system (or driveway, or whatever else it impacts) by first determining the distance over which the acceleration (from fast to stop; some call this deceleration, but it's properly referred to as acceleration and may be shown as a negative value) occurs.
We know if the object lands on the driveway on a cold winter day, it will accelerate quite rapidly. We also know that if the object is "caught" on a dynamic line, which is tied to a leaning tree which bends under the force, and is controlled by an experienced groundie who will let the load run, the acceleration will occur over a greater distance and therefore the force will be minimal over the duration of the acceleration.
So, the rules of thumb may be our best shot. Also, using a dynamometer is a great idea because it gives you the true reading without running through the calculations. Obviously, you can't use the meter everytime (besides, when you rig the piece that was a bit too heavy, it will be too late to check the meter) and we can't do demonstrations with every imaginable piece of wood.
Do control the variables you can: Keep your block and hitch as close as possible when blocking down; teach the groundies how to let the line run effectively.
On that note, how do some of you "let it run" when dropping a piece down onto a speed line?
By the way Glens, I do not intend to slow your progress towards finding the formulas; I spent a while searching my self. If you find something good, I'd love to see it.
