the physics of chopping

MustardMan said:
I am typing from a cell phone, so have no intention to provide a physics lecture. Besides, the last time I taught physics it cost my students 35k a year for the priveledge :D
Click to expand...

We can't afford you. All I can offer is the change from my ashtray in my truck (mostly pennies)... Infi has reduced me to that. ;)
 
Math is great Little bill, but the statement here is just too vague.

Blade hardness, sharpness, and geometry, material being chopped, even climate has been talked about here lately since winter has set in on effects temperature has on tools. The best way to increase velocity on a hand tool is to lengthen it. This is not always practical.

On a white pine, a 24" Cold Steel Latin machete at 18 oz may give a shorter 14" one pound axe a run for the money. Change to a Hickory branch, and I doubt you will even want to use a machete, no matter how long the blade is. On the other hand, no one wants to cut down cat tails with an axe.

Above all, being familiar with your environment, choosing a quality tool accordingly, and a good solid technique is what is most important to chopping effectiveness.

I see that several others have been quicker to the draw but I will throw my drop in the bucket anyways.
 
richstag said:
I would love to hear what both of those guys have to say.

Along with them sharing a bit of their knowledge it is good to have real life results also IMHO:)

As simple as I go outside with a machete next to a FBM an see which one chops better on different types of wood. That is probably going to be the most convincing. With that said, I am sure OP or MM could explain the physics behind my results in great detail:)

Anyhow, I agree and hope they stop by this thread and teach us a thing or two:thumbup:
Click to expand...

They better hurry up because this computer screen is starting to get fuzzy from the alcoholic beverages, I've been pouring down to try to keep my head from hurting any worse.
From trying to decipher this riddle. :D
 
That's what I love about this forum:
everybody throws in their 2 cents worth, and by the time it's all over
I'm several dollars smarter than when I started...
 
d762nato said:
They better hurry up because this computer screen is starting to get fuzzy from the alcoholic beverages, I've been pouring down to try to keep my head from hurting any worse.
From trying to decipher this riddle. :D
Click to expand...

I know! I like pics and vids! Chop chop chop:D

I also like a well presented "physics lesson" from time to time. OP is really smart and he is awesome at explaining things.
 
GrinderMcgee said:
Math is great Little bill, but the statement here is just too vague.

Blade hardness, sharpness, and geometry, material being chopped, even climate has been talked about here lately since winter has set in on effects temperature has on tools. The best way to increase velocity on a hand tool is to lengthen it. This is not always practical.

On a white pine, a 24" Cold Steel Latin machete at 18 oz may give a shorter 14" one pound axe a run for the money. Change to a Hickory branch, and I doubt you will even want to use a machete, no matter how long the blade is. On the other hand, no one wants to cut down cat tails with an axe.

Above all, being familiar with your environment, choosing a quality tool accordingly, and a good solid technique is what is most important to chopping effectiveness.

I see that several others have been quicker to the draw but I will throw my drop in the bucket anyways.
Click to expand...


All good points. :thumbup:

Academia has its place, but my laboratory is outdoors. :)
 
Idaho Jarhead said:
Well, you see, Norm, it’s like this. A herd of buffalo can only move as fast as the slowest buffalo. And when the herd is hunted, it’s the slowest and weakest ones at the back that are killed first. This natural selection is good for the herd as a whole, because the general speed and health of the whole group keeps improving by the regular killing of the weakest members.

In much the same way, the human brain can only operate as fast as the slowest brain cells. Now, as we know, excessive intake of alcohol kills brain cells. But naturally, it attacks the slowest and weakest brain cells first. In this way, regular consumption of beer eliminates the weaker brain cells, making the brain a faster and more efficient machine.

And that, Norm, is why you always feel smarter after a few beers.”
Click to expand...

Speaking of buffalo:

Q: What's the difference between a dog and a fox?

A: Around 6 beers.
 
Last edited:
MustardMan said:
I am typing from a cell phone, so have no intention to provide a physics lecture. Besides, the last time I taught physics it cost my students 35k a year for the priveledge :D
Click to expand...

Can you at least verify that my cup size argument is valid when speaking in terms of momentum so I can celebrate my intellectual prowess with another beverage?
 
kdstrick said:
Academia has its place, but my laboratory is outdoors. :)
Click to expand...

I agree.

Years ago I had a field to clear for a garden, roughly an acre, that had grown up with lots of 2-3" saplings. I was using two blades to clear them, both versions of Cold Steel's All-Terrain Chopper (a modified kukri design) in Carbon V steel with kraton handles: one was 1/8" thick, the other 5/16". Except for weight, edge geometry, and thickness, they were identical.

What I found was that the 1/8" blade was the more aggressive chopper: it could take a bigger 'bite' out of a sapling; but I also discovered I had to work a lot harder with it---even though it was lighter---to make it work. But when I did, it made quicker work of taking down a sapling.

The 5/16" wasn't as aggressive a chopper, but---even though it was heavier---I found I could work a lot longer with it without my arm and hand getting tired. I could hold it looser in my hand, and let the momentum of the heavier blade do the work. It didn't cut down a sapling as fast as the thinner blade could; but it was the one I ended up using most of the time.

It was this outdoors 'lab work' that got me thinking about the advantages of thick-and-heavy vs. light-and-thin blades.

I didn't open up the thread with this, because they weren't Busse blades...

Years later I ended up giving away both blades to seminary classmates who were headed home to Africa...
 
Last edited:
Not a physicist but I can help clear up a couple of misunderstandings on the bullet front ... to begin with in Africa large game calibres were not developed for long range use ... they originate primarily because of the original burn rate available with black powder .... this did not have the ability to burn at the intensity of Nitro powder ... and needing an element of "energy" combined with bullet penetration to kill large game ....large bullets were used. You also need to appreciate lead was the main bullet metal and jacketed bullet technology had also not been developed.

Then along came the Nitro powders which improved things and so did jacketed technology for the bullets. Smaller bullets were able to acquire sectional density and long thin bullets in 6.5mm and 7mm were then capable of penetrating thick cranium bone.

However even the more modern Africa calibres using heavy bullets with special sectional density construction are still not designed for long range...they are designed now more for wound channel creation .... if you are shooting a large animal it takes a while to "bleed out" ....the larger the wound channel ... the quicker this happens.

Using smaller calibres which have expanding bullets has improved matters but they lack penetration for certain shots going sideways through the animal. A head shot would work but it would not always penetrate if it hit at an angle. A heavier bullet is more successful in this sort of application.

So basically there is a lot more to it all than a simple comparison of light knives to light bullets and heavy knives to heavy bullets.

If the human body is the potential "constant" on maximum available swing speed .... the advantage of a heavier blade is apparent ...but then the edge would need to be the same for both. The most successful formula is a sharp heavy knife with a sensibly thin edge profile....that works out in reality and works if you apply the formula's above.
 
Gravity!!!! . . . . . :thumbup:

Any questions? . . . .

There will be a quiz! :eek:

Let's Drink!!!:thumbup:


Jerry :D


.
 
“People love chopping wood. In this activity one immediately sees results.” - Albert Einstein
 
I haven't read any of these posts except for 1 or 2 involving physics and why it doesn't apply because a more massive blade will "bite" better.

In this analysis, we're assuming blade mass is the same. velocity is the only variable. If we're ONLY looking at energy transferred to the block of wood (ALSO disregarding friction as it slides through the wood) then kinetic energy is 1/2 mv^2. Therefore doubling, tripling etc. velocity has a much more drastic impact (no pun intended) than doubling, tripling, etc. the mass.

Edit: We also assume that thickness, grind, and steel of the blade remains the same. (Ceteris paribus)
 
Let's not even get into batoning, or we'll have to discuss torque to a greater extent.:eek:
 
Ankerson said:
Doesn't work that way in real life. ;)

speed can't compensate for lack of mass and weight.
Click to expand...


Actually it can. Let me fire a .5 oz stone at 400mph into your skull. I think your opinion will differ then.

(I don't mean to be nasty, just proving a point.)
 
ans7812 said:
Actually it can. Let me fire a .5 oz stone at 400mph into your skull. I think your opinion will differ then.

(I don't mean to be nasty, just proving a point.)
Click to expand...

remember the old myth that dropping a penny from the empire state building and hitting someone at the bottom would kill them? but it doesn't, because of weight of the penny. It's definitely got the speed, but it doesn't have the mass to do it.

And from what I've read the a bullet constantly looses acceleration once it leaves the barrel, but a knife stab or chop picks up acceleration until it hits the target or passes a critical point in the swings arch.

just chiming in :)
good discussion we got going
 
Jack Shen said:
remember the old myth that dropping a penny from the empire state building and hitting some at the bottom would kill them? but it doesn't, because of weight of the penny. It's definitely got the speed, but it doesn't have the impact.
Click to expand...




...

Again, cell phone typing, so I'm not gonna go into detail ere, but you are wrong. It's not that the penny has plenty of speed, it's this little issue of terminal velocity and the poor aerodynamic profile of the penny, which generates lots of fluttering turbulence which prevents the penny from going fast enough to act like a bullet.
 
You must log in or register to reply here.
Back
Top