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Ballistics pendulum

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Ballistics pendulum

Unread postAuthor: koolaidman » Tue May 13, 2008 11:03 pm

I have not heard one mentioned, through searching, and its not on the wiki. Has anyone made one? I know it's not hard. My question is not how to make one. Im just wondering if it's really effective. about how much energy is lost ( not transferred) using this method?
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Unread postAuthor: MrCrowley » Tue May 13, 2008 11:30 pm

Someone mentioned it in the 28,000v Electro-Thermal Gun thread...


Edit: I don't mean you didn't search hard enough, just pointing you in a direction as I have a limited knowledge of them you might pick something up from that thread.
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Unread postAuthor: Eddbot » Tue May 13, 2008 11:55 pm

too used to pwning noobs about not searching? :D
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Re: Ballistics pendulum

Unread postAuthor: Ragnarok » Wed May 14, 2008 6:59 am

koolaidman wrote:Im just wondering if it's really effective. about how much energy is lost ( not transferred) using this method?

If that's your exact question, the answer is "A lot".

However, that's not important - because it doesn't work on energy conservation, it works on momentum conservation, a different, although not completely unlinked physical concept.

And there, it assuming the pendulum isn't set spinning by an off centre hit, it doesn't waste any. It's very effective - until the introduction of electronic chronographs, it was the primary method of determining ballistic velocities.

If done well, you can get a good, accurate and reasonably precise result.

However, unlike with a chronograph, it stops the projectile - which in some ways is good, some ways bad. You don't need to worry so much about the projectile heading down range after firing, however, you can't measure the velocity on a shot if you intend to shoot a target on the same shot.
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Unread postAuthor: SpudFarm » Wed May 14, 2008 7:05 am

[youtube]http://youtube.com/watch?v=WIow_fvCfW0[/youtube]

Lardas test on the ETG
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Re: Ballistics pendulum

Unread postAuthor: D_Hall » Wed May 14, 2008 9:32 am

Ragnarok wrote:However, that's not important - because it doesn't work on energy conservation, it works on momentum conservation, a different, although not completely unlinked physical concept.

Not completely unlinked?

I gotta jump on that...

It's TOTALLY linked. "Not completely unlinked" implies a relationship; but one that may not be too strong.

Kinetic energy is the integral of momentum just as position is the integral of velocity.

They aren't kinda sorta linked. They are flip sides of the same coin forged in the furnaces of physics.
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Re: Ballistics pendulum

Unread postAuthor: koolaidman » Wed May 14, 2008 9:33 am

Ragnarok wrote:[However, that's not important - because it doesn't work on energy conservation, it works on momentum conservation, a different, although not completely unlinked physical concept.

And there, it assuming the pendulum isn't set spinning by an off centre hit, it doesn't waste any. It's very effective - until the introduction of electronic chronographs, it was the primary method of determining ballistic velocities.


well, ragnarok, energy conservation is an integral part of that whole system. I reffered to conservation of energy because it's more encompassing. by that i mean, how much initial kinetic energy of the projectile, is finally converted into gravitational potential energy of the block.
I think I supposed the biggest loss would be the collision. My main ammo is usually paintballs or carrots, both of which do not exactly enact the most inelastic collision.
That brings me to my next question, what material should the actual block be?
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Re: Ballistics pendulum

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Unread postAuthor: jimmy101 » Wed May 14, 2008 3:38 pm

How much energy is "lost" is mostly dependent on two things; (1) Friction of the main axle and (2) air drag on the pendulum's bucket. If built properly both those can be minimized.

A homemade chronometer is simpler, cheaper and more accurate.
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Unread postAuthor: psycix » Wed May 14, 2008 4:23 pm

The ballistic pendulum is not very precise not only to measuring faults, but also because of the following.

It depends on what the projectile does:
-Stop dead and fall to the ground (adds ALL kinetic energy)
-Get stuck in the pendulum (adds mass to it, and ALL its kinetic eneregy)
-Bounce back (action -> reaction, so the bounceback makes the pendulum swing even further??? <=question marks, not sure about this)
-Splatter out into pieces (somewhere in between of stop dead and bounce back, this is near uncalculatable)

Also, if the tip of the projectile gets flat, or the surface of the pendulum gets a knock in, I can see kinetic energy being lost.
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Re: Ballistics pendulum

Unread postAuthor: Ragnarok » Wed May 14, 2008 4:25 pm

D_Hall wrote:They aren't kinda sorta linked. They are flip sides of the same coin forged in the furnaces of physics.

Curses.
I know that, but I was rushing the post because I had some other things to do, and I didn't put it through my normal quality control against such total brain farts. My mistake on that one.
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Unread postAuthor: potatoflinger » Wed May 14, 2008 4:29 pm

I know that there is a chapter in Backyard Ballistics about ballistics pendulums, it might be worth a read to find out how much energy is lost etc.
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