1. Established Member
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## Question or rather clarification about Kinetic energy

I am a bit confused about this. I was purchasing some Arrows for my bow recently and wanted some light weight arrows for a flatter trajectory. I was looking at some really lightweight carbon arrows and The man at the bowyers shop it wasn't ncessessary. I asked him why and he told me that the draw on my bow would reach the upper bounds of the arrows capability way too soon and the remaining energy would be directed back into the bow. Excess energy being directed into the back of the bow is common knowledge, thats why you don't dryfire bows.

Now I was under the impression that an object had no upper bounds of kintic energy. I got home and looked it up on Wikipedia and found this definition:
Kinetic energy (also called vis viva, or living force) is energy possessed by a body by virtue of its motion. The kinetic energy of a body is equal to the amount of work needed to establish its velocity and rotation, starting from rest.
So that got me thinking, If it's related to the amount of work needed to put the arrow into motion, then 1) why is Excess energy directed back into the bow, and 2) As long as an arrow will retain its integrity, the amount of force behind the arrow would only increase it's Kinetic Energy.

Now I realize some arrows are rated for certain draw weights or they will come apart if shot from a fast bow. Thats not what I am referring to, the Carbon Arrows I was looking at were WELL within the specs for my bow.

So my question is this. Does an object have an upper bound for Kinetic energy or does the kinetic energy increase limitlessly based on the force putting it in motion? Is it based on Mass of the Object or is it based on the Work needed to put the object in motion?

2. I think the problem with bows and arrows is that not all the energy stored into bending the bow is transferred to the arrow.

The arrow cannot be faster than the string of the bow when you release it.
The lighter the arrow, the quicker the arrow reaches that velocity.
Adding a tiny little push from the string, the arrow is just fast enough to be no longer in contact with the string, and the remaining energy stored in the bow does not go into the arrow.

The lighter the arrow, the less amount of energy is required to reahc the "muzzle" velocity, the more enrgy is left in the bow.

It is then up to your arms to deal with it.

Anyway, there is no bound to kinetic energy.

3. This is just an educated guess, but I would think it would have more to do with how much energy the bow can put into an arrow. An arrow is capable of acquiring any amount of kinetic energy, but a bow only has a very brief time to impart that energy and can't impart all of its energy to anything but a comparatively heavy arrow. If the arrow is too light, so that there's a large difference between how much kinetic energy a bow could impart and how much it does impart, then the difference must be absorbed by the bow, i.e., it approaches dryfiring the bow as the arrow gets lighter.

EDIT: I think papageno and I are saying pretty much the same thing.

4. Originally Posted by ToSeek
EDIT: I think papageno and I are saying pretty much the same thing.
Oh yes! 8)

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OK thanks, that makes sense. I may have misunderstood what the man was trying to tell me. Of course, after I had left and started thinking about it I wanted to turn around and ask him why the heck they make arrows like that if they are essentially useless.

At any rate a flatter trajectory means less differential between my 5, 10, 20 and 30 yard sight pins. Oh well, I'll just keep it as it is rather than change the wholse setup.

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I'd think it'd mean you'd have to adjust your bow-pull. And it might be more for sport-shooting rather than hunting; where the impact is not as important as being on target.

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Originally Posted by PatKelley
I'd think it'd mean you'd have to adjust your bow-pull. And it might be more for sport-shooting rather than hunting; where the impact is not as important as being on target.
Actually they ARE for sport shooting, which is the application I was purchasing them for. I definitely would rather have heavier arrows for Hunting, because for hunting, any shot more than 20yards will almost assuredly be a miss. The heavier arrows have more penetrating power, the lighter arrows only nead to pierce a few centimeters of Latex Foam that make sup the 3D target

8. It sounds like the lighter arrows make good sense. So the trick is to get that energy into the lighter arrows. Can you use a stiffer bow which would produce a faster string speed, I think?

9. Only up to a point

10. Originally Posted by A Thousand Pardons
Only up to a point
I'm sure you are right as this is quite an art. Nevertheless, we might come up with something that would put physics to work on his behalf.

There is bound to be some way to increase string speed with the same pulling force. This might change his release profile which could affect his aim negatively (or maybe improve it).

11. Order of Kilopi
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Kinetic energy is among the most potent forces that we know. Some of the worst damage done to the Mythbuster dummy ('Buster) resulted from a simple drop into water--which almost tore his arm off. They exploded him many times-scorched him pretty good--but that drop in the water did about the most structural damage--at least early in the series.

Orion would have worked because we know that spheres survived nuclear explosions and were recovered. But the problem was getting enough momentum--not energy.

Tonight's episode where they drop some airline seats is therefore the most dangerous stunt to date. They are careful about explosives--but even a short drop can create havoc with your spine.

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Originally Posted by publiusr
Kinetic energy is among the most potent forces that we know.
It's really not, since kinetic energy and force are distinct concepts within physics.

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