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Physics Question

#21
Few more questions:

1) field tips, three blade broadheads, 4 blade broadheads, or mechanical broadheads?
2) carbon fiber or aluminum arrows - gotta think about weight as well as the elastic modulus of the arrow shaft material.
3) .38 special. Seriously? That's a has-been caliber. Go full on .357, or jump over to the fancy "new" 9mm or .40 S&W.
4) Is it an African or European Swallow?

ahh... I got beaten to the punch on the MP reference.....
 
#23
Momentum tells you how much force with how much time you need to use it to slow the speeding thing from speed A to speed B.

I think the damage done in a collision is proportional to the kinetic energy that is "disappeared". Mythbusters' rocket sled experiments illustrate this well. Zoom, Boom, not much left in one piece.
 
#26
FingerDub said:
If you had a compound bow and arrow, facing off against a single .38 caliber cartridge, what would be the relative distance between the launch of the arrow hitting a target with the same force as a .38 cartridge from an equivalent distance? Would the .38 cartridge be 200m away while the bow would be 80m? How would you figure that out? I know that the arrow has more weight, so more force. But the bullet has more velocity...How could I calculate the exact distance that would make both exert the same force on the same target. How far away would the bow and arrow be and how far away would the gun be?
Click to expand...


There is no simple way to calculate momentum or energy values vs range.

The best way to find such values would be to examine ballistic data for each of the two projectiles.

Here is an example of arrow ballistics:

http://i129.photobucket.com/albums/p236/tfox_02/Picture038.jpg

You would need a similar table based on the .38 bullet ballistics.

-
 
#27
Hey, at least you don't have to take into account the curvature of the Earth, like the MK 86 GFCS does :smug:

2qmd7yh.jpg
 
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#29
Weight of the arrow and draw weight of the bow will be significant factors - actually less draw weight of the bow than velocity of the arrow of a given weight.
Many hunters use heavier arrows as the additional mass provides significantly more striking force. There's only so fast you can get an arrow to go.
 
#31
All things being equal the bullet will supply more energy to the target because of the way it behaves upon impact. Bullets, unless specifically designed not to, mushroom thus spreading the damage and kinetic energy. An arrow pierces the exterior with sharp edges designed to enter it's target easily.

For a graphic display take a paper bag and pierce it with a knife. Then do it with your finger. Two different ways to do the same thing with very different results.
 
#32
Let's say the arrow is an average arrow weighing 25 g and the compound bow is average and fires 100 m/s. Let's say the gun is a .38 Special with a firing velocity of 540 m/s and a slug weighing 6 g. It is a clear day with no wind, humidity is 78%, temperature is 60 F, and barometric pressure is 29. You are also standing on a 130 ft platform so you can hit the target with the muzzle aimed upward at an angle of 45 degrees.

With that information, you need to be around 750 meters away for the bullet to slow to a velocity of around 200 m/s or 450 mph for the kinetic energy of the two projectiles to be the same if the arrow is fired point blank. The arrow will of course do more damage under these conditions, because there is no way the target gets hit by the bullet.

Good luck with the shot.
 
#33
Funky Ghost said:
All things being equal the bullet will supply more energy to the target because of the way it behaves upon impact. Bullets, unless specifically designed not to, mushroom thus spreading the damage and kinetic energy. An arrow pierces the exterior with sharp edges designed to enter it's target easily.

For a graphic display take a paper bag and pierce it with a knife. Then do it with your finger. Two different ways to do the same thing with very different results.
Click to expand...
This is a poor example. The bullet is traveling roughly 8 times the speed of the arrow. The arrow weighs roughly 4 times the bullet. The bullet has roughly 32 times the energy of the arrow. Imagine the damage if an arrow was fired at 800 mph.
 
#34
James Collins said:
This is a poor example. The bullet is traveling roughly 8 times the speed of the arrow. The arrow weighs roughly 4 times the bullet. The bullet has roughly 32 times the energy of the arrow. Imagine the damage if an arrow was fired at 800 mph.
Click to expand...

How do you come to the 8x speed figure? Bullet load out matters. Grain of powder matters. The weapon barrel matters. Much is involved. As a person who has fired more than a few weapons, and loaded more than a few of my own shells in my time, I can tell you that muzzle velocity and arrow velocity can come closer to even than you might think. A well made, high end compound bow can exert tremendous force and exceed some bullets. Granted this is not the exception but it does bear mentioning.

In my example I had said all things being equal. This should have informed you of the direction I was going. A bullet transfers more energy because it is designed to. An arrow pierces because it is design to get to a vital organ. It kills by organ damage. Bullets kill by area damage which includes organ damage but can also include trauma that leads to a bleed out. ANYTHING going 800 mph will do drastic damage. I would suggest your example is poor.
 
#35
Funky Ghost said:
How do you come to the 8x speed figure? Bullet load out matters. Grain of powder matters. The weapon barrel matters. Much is involved. As a person who has fired more than a few weapons, and loaded more than a few of my own shells in my time, I can tell you that muzzle velocity and arrow velocity can come closer to even than you might think. A well made, high end compound bow can exert tremendous force and exceed some bullets. Granted this is not the exception but it does bear mentioning.

In my example I had said all things being equal. This should have informed you of the direction I was going. A bullet transfers more energy because it is designed to. An arrow pierces because it is design to get to a vital organ. It kills by organ damage. Bullets kill by area damage which includes organ damage but can also include trauma that leads to a bleed out. ANYTHING going 800 mph will do drastic damage. I would suggest your example is poor.
Click to expand...
In your example, it takes more force to put a finger through a bag. So the energy from the finger is higher, leading to more damage. A blade is designed to focus the energy so it will cause less damage overall, but more exactly where the blade contacts.

You can find a range of velocities for the bullet and arrows. The arrows are significantly slower. For example, bullets are faster than sound. The OP is talking about 0.38 so I used the median velocity on that particular type of gun with a normal sized 130 grain or 6g bullet. The median compound bow speed I found was 330ft/s topping out at maybe 400ft/s with a 400 grain arrow. That should be around 100 m/s 200mph. I think I had a unit error, my apology, where the bullet should be 800 m/s instead of mph. I'm open to any other relevant data though.

My point is it is the energy that does the damage at a higher velocity, and has less to do with the characteristics of the projectile. projectile.

Edit: If all things are equal, the velocity would be the same. For example, I don't want you to throw an arrow at me, but you could throw the bullet at me.
 
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