Difference in destructive power between a heavy stick and a light stick?

[yungman]

I am practice stick fighting for self defense. I have a question I don't know how to judge. Say if I have a 6oz and a 12oz stick both 28" long. I swing them to hit an object, assuming I have the same strength, obviously the velocity is faster with the lighter stick and slower with the heavy stick. Which one will have more destructive power. In another words, which one is better for self defense?

For calculating energy, P=1/2 * m * v^2. Obviously the faster the v, the more power.
But for momentum, it's mv, the difference is not as big.

Also, I have no idea how big the effect of air resistance on the velocity if the lighter stick is thinner.

Thanks

 

[Vanadium 50]

Consider the two extremes. Which would be more effective - a twig? Or an entire redwood?

 

[Lnewqban]

Because the reaction time of the other person is limited, speed is your friend.
But the power (force times velocity) that your arms and hands can deliver is also limited.
I would stop increasing mass of the stick when its speed starts suffering.
Also effective impacts on sensitive zones do not need much force, only precision and surprising speed.

 

[yungman]

I am confused, what is stopping power and destruction power ( I don't know how to put it better)? Is it P=1/2 * m *v^2, or P=m*v? I never know the answer. Like even the ballistics for bullets, how do you compare a lighter bullet at higher velocity to a heavier bullet at lower velocity? Which formula you use?

Also, is it the KENITIC ENERGY or the MOMENTUM that is the stopping power?

Thanks

 

[Ibix]

Which formula you use?

Neither. It's a lot more complex than that. For example, a knife does not make your strikes stronger or faster, but makes them a lot more likely to be lethal.

Human beings are complicated composite structures of rigid bone and elastic meat. There isn't a simple model of what will do more or less damage. For example, if I hit your hand with a wooden plank I might break bones, or if you've formed your fist properly and angled it just right you might break the plank (this is just board breaking, and you can find plenty of videos of it if you haven't seen it). In both cases the plank has the same energy and momentum - you just dealt with it differently.

 

[yungman]

Well, just assume other conditions are the same, what is the difference between large bullet at slower speed vs lighter bullet at higher speed. How do you calculate?

Same as a lighter stick at faster speed vs heavier stick at slower speed?

 

[Vanadium 50]

Now you're buying a gun?

 

[Mark44]

Is it P=1/2 * m *v^2, or P=m*v?

The first formula is kinetic energy, and is usually written as $E = \frac 1 2 mv^2$. The second is for momentum, p. P (upper case) is used for power, as I recall.

A mass of 1 kg moving at 10 m/sec has a kinetic energy of $1 \cdot 10^2 = 100$ joules.
A mass of 0.5 kg moving at 20 m/sec has a kinetic energy of $0.5 \cdot 20^2 = 200$ joules.

Both masses have the same momentum.

 

[Ibix]

Same as a lighter stick at faster speed vs heavier stick at slower speed?

The basic problem with your question is that fighting isn't physics, and "stopping power" is a fighting term, not a physics one. There are certainly physics questions that you can answer - @Mark44 has calculated the kinetic energy and momentum for two different objects, for example. They just don't relate simply to anything useful to fighting.

"Stopping power" certainly has something to do with energy and momentum, but only with the amount that's absorbed by the target. How much energy and momentum you can deliver to a stick (let alone to your target) depends on things we don't know. For example, how well do your muscles work at different speeds (can you really move the lighter stick twice as fast...?)? How good your stance is when you strike will affect how much energy goes into rocking you backwards instead of swinging the stick forwards. How long can you keep swinging the heavier and lighter stick effectively? That's just off the top of my head, and I haven't got into how the opponent is moving. Essentially, any mathematical model you can construct here is either too simple minded to be helpful or has too many variables that you either can't quantify or will vary wildly from moment to moment.

 

[sophiecentaur]

Consider the two extremes. Which would be more effective - a twig? Or an entire redwood?

Those two extreme cases demonstrate that the power and mass of the arm (and length etc. etc.) are equally relevant. With no stick at all, you could just punch the victim and do damage but a heavy stick would hardly get going so could do no damage at all.

When you are considering Momentum, it's essential to include the momentum of the arm and you need to match the individual to the stick as it would be the total momentum that's relevant. It's probably more instructive to discuss baseball and cricket bats and how far they can knock a ball. Much easier to define and measure the effect. (and get consistent results from experiments). The psychology of hitting a human (for both people involved) tends to mess up results so that's probably something to move on to, once you have sorted out the bat / ball scenario.

 

[Bystander]

This is "Optics?"

 

[sophiecentaur]

Light stick light Sabre?

 

[Doc Al]

This is "Optics?"

Moved to "Mechanics", for now.