more real-world blade physics

LittleBill

LittleBill

Joined
Jan 25, 2010
Messages
86
two knives, of equal weight: one with an 8" blade and the other with a 12" blade:

when both knives are swung through the same arc, in the same amount of time,

the tip of the 12" blade is going to be traveling a lot faster than the tip of the 8" blade (because it's covering more distance in the same amount of time);

and therefore will be striking with a lot more force on the target (since force is proportional to velocity squared)...

so---everything else being equal---a longer blade is going to be a better chopper than a shorter blade...

or: a lighter, longer blade will be as good of a chopper as a shorter, heavier blade...

yes?
 
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Force= mass*acceleration. Force is due to acceleration which is rate of change of velocity, not velocity or change of velocity.
 
Please, stop with the attempted physics threads - you're going to give me an anyeurism :eek: :D :D

one of us needs to drink more, and I hope it's me, because these threads are gonna drive me to the bottle :thumbup:
 
...tune into next week's episode of Kentucky Windage Gone Wild meets the Box o' Woodsman's Truth where the questions on everyone's mind will finally be answered:

your mom's Pie Server vs Grandma's Butter Knife - which one is best for chopping through frozen blocks of cream cheese for spreading on bagels while summering in the North Pole? does the extra length of the Pie Server make a difference? and, what sharpening angle is best for spreading cream cheese at high swing velocities?
 
Yes the longer the blade the more momentum and potential energy is stored in the blade. This momentum is also the reason why longer and heavier blades are slower when you need to get them to swing or when you want them to stop swinging or change direction. That is why of the tip a whip, that carries no real "weight" is capable of inflicting massive pain because of the high velocity it travels.
 
everything else being equal. Of course edge geometry will also play a big part - i.e. do you want a thin edge for slashing through light vegetation or a thicker convex edge for flinging wood chips w/out the edge binding in the wood with each chop.
 
DowntownDM said:
...tune into next week's episode of Kentucky Windage Gone Wild meets the Box o' Woodsman's Truth where the questions on everyone's mind will finally be answered:

your mom's Pie Server vs Grandma's Butter Knife - which one is best for chopping through frozen blocks of cream cheese for spreading on bagels while summering in the North Pole? does the extra length of the Pie Server make a difference? and, what sharpening angle is best for spreading cream cheese at high swing velocities?
Click to expand...

:eek: What he said! :D :D :D
 
MustardMan said:
Please, stop with the attempted physics threads - you're going to give me an anyeurism :eek: :D :D

one of us needs to drink more, and I hope it's me, because these threads are gonna drive me to the bottle :thumbup:
Click to expand...


Agreed.

And as far as the bottle goes: I expect there are quite a few of us who would be willing to make that drive with you, brother... I know I'm there for you...
 
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Your supposition is correct and it can be proved in a variety of ways.

Impact-relevant, use Impulse for amount of force that changes hand. Since Impulse = delta momentum, a greater velocity given the same mass will produce a bigger impulse and therefore a better chop.

Using change in kinetic energy (0.5*m*v^2), mass coefficient is a linear multiplier while velocity is a quadratic multiplier (v^2). So velocity will produce a greater effect.

Using torque, as the swing will be in an arc and therefore rotational in nature, the centre of mass for a longer blade will be out further than a shorter blade, so torque, F x d(centre), would be higher as well.

*end geek-out*
 
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