? Physics ?

[John Ellison]

Another post has me thinking about an old argument. If you hear a noise above while falling a tree, do you have time to get out of the way. As opposed to actually seeing something fall. I know there are so many variables that it might be pointless.
Lets assume that it falls from 50 feet immediatly with the noise. Faller has average reaction time and ave. speed. Falling object is whatever size makes it easy to figure. One foot long? I know sound is 1100 fps but not much more of whats needed. Can anybody figure it out without going to a lot of trouble?

 

[upandcommer]

average acceleration due to gravity is 32 f/s or 9.8 m/s average reaction time is .2s so to answer your question you better be quick sound travels at 768 mph so you hear it .0762 seconds after the break then under gravity it accelerates to 32f/s in the first second so you might have a whole second to move but your average reaction time is .2s so you miss the first .2 seconds of time to run average foot speed over uneven terrain is 6 mph. so you'd be scared and fight or flight kicks in. You might survive but more often than not you are gonna get hit if you are in the path of said falling object so wear a hard hat look up and asses any hazards before you start.

 

[Stihl 041S]

Nother physics

If a tree falls in the forest and it hits a mime, does anybody care?

 

[infomet]

If you make a statement while deep in the woods and your wife doesn't hear it, are you still wrong??

 

[upandcommer]

yes if you make a statement in the woods and your wife is not there you are probably still wrong in her eyes if the mine explodes no one cares and the physical world is still governed by gravity and the like.

 

[Stihl 041S]

Nother

Speeding is a rule, gravity .is a law

 

[Gologit]

John,we need a guinea-pig for this experiment. We could find somebody here on the forum to volunteer and then test out your theory in a real world environment. Any volunteers?

 

[Jim Mesthene]

I was once sitting by a fire with a friend (35 years ago, when I was younger and quicker). We heard a loud crack and looked up; a large branch had broken off, about 40 feet up, presumably from the hot air rising from the fire.
We were both about 15-20 feet away by the time the 6" diameter X 20 foot branch hit where we had been sitting. Adrenaline helped.

 

[Woodie]

If a tree falls in the forest and it hits a mime, does anybody care?

Or, like Steven Wright says, "If you shoot a mime, do you have to you use a silencer?"

 

[drmiller100]

acceleration of gravity is 32 feet per second squared.
that means something travels 32 feet the FIRST second. Quite a bit faster the second second (hehe!!!)

secondly, so you are running a loud, noisy, chainsaw falling a tree, and you HEAR a branch break 50 feet up???? Not likely.


Thirdly, you don't have to run away. You can just step aside, if you have time.

 

[Gologit]

acceleration of gravity is 32 feet per second squared.
that means something travels 32 feet the FIRST second. Quite a bit faster the second second (hehe!!!)

secondly, so you are running a loud, noisy, chainsaw falling a tree, and you HEAR a branch break 50 feet up???? Not likely.


Thirdly, you don't have to run away. You can just step aside, if you have time.

And if you're wearing the super hearing protection ear muffs that are so much in favor now you're not going to hear anything either.

 

[doc874]

Once the veil of darkness has descended upon you from the force of the blunt trauma, "its all pointless"! "YES YOUR STILL WRONG," haven't you married guys learned anything yet? Lol.

 

[turnkey4099]

average acceleration due to gravity is 32 f/s or 9.8 m/s average reaction time is .2s so to answer your question you better be quick sound travels at 768 mph so you hear it .0762 seconds after the break then under gravity it accelerates to 32f/s in the first second so you might have a whole second to move but your average reaction time is .2s so you miss the first .2 seconds of time to run average foot speed over uneven terrain is 6 mph. so you'd be scared and fight or flight kicks in. You might survive but more often than not you are gonna get hit if you are in the path of said falling object so wear a hard hat look up and asses any hazards before you start.

I think the .2s is way optimistic. In driver education material 1.2-1.5 sec is pretty much accepted for an unexpected event. That takes into account every thing from the time to recognize something happened, make a decision, then actually -do- something about it. I know a reaction timer I had in memory would show me at about .23 sec for an "expected" event. Saw one hot-shot kid who could get it down to .16. That was a timer that had you sitting with your finger on thebutton and watching for a very obvious change on the screen.

http://www.spikything.com/games/reaction/

I don't know if that still plays

Hmmm...worse than I thought, I went into my files and found this:

Back when I got interested in the subject; I got curious about reaction times so went googling. Here are two URLs that I scanned quickly
(they were the first two on the hits).

http://www.visualexpert.com/Resources/reactiontime.html
http://www.general.monash.edu.au/muarc/rptsum/hfr12.htm

Both sites accept 2.5 sec is the accepted total reaction time.

-------------------

I think the 2.5 sec would be for someone asleep at the wheel .

Harry K

 

[smokechase II]

variables

John; You didn't want this but here goes anyway.

If the limb is well stocked with leaves/needles. That will slow down its descent appreciably. The terminal velocity of that limb will be a slower peak speed than the terminal velocity of say a dead, needle free broken limb that is 4" in diameter and 3 feet long.
I think, that means I'm ready to be taken to the cleaners on this, that most limbs with lots of needles/leaves will reach their terminal velocity at about 50 feet. I.e., they will not still be doubling their acceleration rate every 32 feet.

The limb with very little surface area in the way of leaves, (that will not have the same air resistance), will not only be going 40 mph at the 50 ft mark but will still be accelerating. So fear the limb at 100 feet just as much, perhaps more. The increased time from that 100 foot fall is not going to be a doubling of the 50 foot fall. But its speed may well be double or even more, depending on air resistance factors.

I'm also going to suggest that most horizontal limbs will not shear off and drop immediately. (Possible exceptions Larch and some other very brittle woods, but this would be rare). Most of those limbs will partially break; make a noise, then bend over till they get near vertical and the remainder of the holding wood breaks. This could represent a little additional time for recognition and escape.

A limb that has broken to some degree and is already hanging vertically represents a greater danger than most horizontal limbs. Not only is part of its structural integrity gone but it is ready to drop faster. This could also be true of slabs up high. They could well be ready to fall immediately.

In the same category is a limb that is clear and is resting on other limbs(s). It also could be ready to go instantly.

{Sound is of little value to a sawyer. One additional advantage to wedging over a tree is you don't have that noise maker going. But that hazard above you was there when you were cutting prior to wedging with the noise maker running.}

Of course limbs that have to work their way through other limbs will provide additional time for recognition escape.

Has anyone ever video taped themselves or had a buddy clock the amount of time they are actually looking while falling?
For all of us, don't put yourself under a widowmaker.

 

[smokechase II]

reaction time trivia

turnkey4099:

I did some searching for Ben Jonson's, (Olympic sprinter disqualified for steroids), reaction time. I remembered something about it being below what "they" believed was possible for humans.

Came across this; "Fastest ever recorded 'legal' Reaction Time: 0.100s, Jon Drummond (Monaco GP 1993)"

I'll just go ahead and admit right now that I'm not going to match that with my current training regimen.

 

[PA Plumber]

Avg. .178 Pretty neat. I still don't want thumped on the noggin though!!

 

[Jim Mesthene]

acceleration of gravity is 32 feet per second squared.
that means something travels 32 feet the FIRST second.

Actually, it falls 16 feet during the first second. It's travelling at 32 fps only after the first second.

 

[Woodie]

acceleration of gravity is 32 feet per second squared.
that means something travels 32 feet the FIRST second.

Actually, it falls 16 feet during the first second. It's travelling at 32 fps only after the first second.

Jim, you should know from the torque thread that Doug is NEVER wrong when it comes to math and physics... :hmm3grin2orange:

 

[Lakeside53]

Nope.. that only for high mass low drag objects.. A branch has drag due to the air resistance and travels slower Remember the old experiments - dropping a horse and a mouse down a mine shaft??? or the a feather and a stone from a tower...

Heck, I've seem entire tree top "float" down".:jester:

 

[gasman]

I've heard in the US Civil war that cannon balls could be seen coming for hundreds of yards bouncing along the ground. I bet one coming straight at you is very hard to see but from the side would look like slow motion.

Maybe one could see the dirt and stuff being kicked up as it bounced.