How’s my physics?

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viking33
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Re: How’s my physics?

Post by viking33 »

DaveA wrote:The extra padding using the beret with the badge, is not to bad of a joke.
But while meeting the requirements for law enforcement, we had to fire the shot gun a few time. We had several in the group that had never fired a riffle let alone a shot gun.

So after the demonstrations on how it is to be done, some one suggested that if one was to hold the shot gun about a 1/2 of an inch from the socket of the shoulder it would not kick quick as much. Lease most of you do know the result of this.

Another step in this testing was firing the shotgun from the squatting position. Many were able to fire it OK, but ended up being flipped on to their back.

Yes this was a some what fun day for those of us the have been around fire arms most of our lives and forgot all of the tricks that were pulled on us when we were learning about guns.
Yet you see pics of guys firing an M-16 and the stock is held over the top of the shoulder, not even close to them? Don't think they are aiming the thing!
BOB
:massachusetts: :usa:
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If I agreed with you we'd both be wrong.

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ChrisGreaves
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Re: How’s my physics?

Post by ChrisGreaves »

HansV wrote:I wouldn't be surprised if the trajectory of the bullet becomes erratic/unpredictable at the top of its trajectory, because of its low speed there...
Interesting thought.
In theory we are outside any Heisenberg sort of uncertainty, but almost certainly still within the realms of chaos theory.
At this stage I can contemplate some sort of probability distribution (which could be verified by sampling thousands of firings and landings) which ought, at least, to enable us to verify the calculations based on wind speed, altitude, temperature and so on.
That is, even the chaos can be reduced to a formula that would help us to verify the remainder of our formula.

So I am left with my original thoughts on atmospheric variables PLUS some sort of probability distribution based on "tumbling".
Yours in deep thought
Chris
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ChrisGreaves
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Re: How’s my physics?

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BobH wrote:You would have to be able to control the trajectory of the descent because wind, atmospheric humidity and other factors are variable; therefore having read it before firing, one cannot assume that they will remain constant and probably a few million other reasons.
Hi Bob.
I am (as always :grin: ) tempted to disagree with you.
The flight of the bullet is short-term (compared to weather) say about one minute, maybe two.
If I can know the weather in terms of temperature and wind speeds and humidity in, say, fifty-foot steps to the maximum altitude (two miles), then my theory is that I can factor those data into my formula and adjust the alignment of the barrel.
I am, of course, thinking computerized calculations accurate to the ten-second interval, preparing the rifle alignment for an episode of about two minutes duration.

Are there any other factors I should take into account?
Cheers
Chris
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Re: How’s my physics?

Post by ChrisGreaves »

PJ_in_FL wrote:... rotation of the earth and altitude of the rifle will need to be factored in. ...
Hi PJ.
Why should rotation of the earth be factored in?
The bullet and the rifle barrel have zero velocity relative to each other at the time of firing.
Whatever their latitude, they have the same speed relative to the surface of the earth, that is, zero.
I know it is sung that the earth rotates at nine hundred miles an hour at the equator, (and less as we near the poles), but whatever the speed (relative to what?), the rifle embedded in rocks, and the bullet traveling away from the barrel, start off, and should end up, with a velocity of zero relative each to the other.
Cheers
Chris
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ChrisGreaves
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Re: How’s my physics?

Post by ChrisGreaves »

Leif wrote:... did you want the bullet to return nose first or bottom first?
Bottom first. I forgot to specify that.
This factor does bring in "tumbling" as a real problem.
If I am able to calculate/predict tumbling, then I might have to factor in the amount of explosive charge (that is, initial energy) to try to have a trajectory that resulted in the bullet base being foremost (rearmost?) when it arrived back at the barrel.

I am using a rifle/bullet as a vehicle for physics. If I have to I will go back to a cannon and a spherical ball, which eliminates the tumbling problem, I believe.
Cheers
Chris
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ChrisGreaves
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Re: How’s my physics?

Post by ChrisGreaves »

Roderunner wrote:If it fell bottom first, it would take longer as it's less aero-dynamic (streamlined).
This is true; for which, Thanks.
Of course, in this we are both assuming the "no tumbling" scenario.
Tumbling would involve more complex calculations on aerodynamics for each cycle of rotation of the bullet as it tumbled back towards the barrel, but I suspect that those calculations are ones I should have been able to do around the time I stopped practicing calculus some 50 years ago.
Cheers
Chris
P.S. see also my comments five minutes ago on a who-cares about tumbling cannon-ball"
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Re: How’s my physics?

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BobArch2 wrote:Embedding the rifle in rocks is not going to make for a smooth exit of the bullet when fired. ...
Not exactly.
Hi Bob.
I just said "embedded in rocks", but I sure didn't mean three fist--sized rocks.
Attached are two images of how Canadians erect telegraph and power poles in swamps.
A similar practice is followed on the highways around Alaska, certainly on the route Dease Lake - Whitehorse-Fairbanks.
Expand the term "rocks" to mean "rocks embedded in a matrix of concrete in a five-foot high twelve-foot diameter galvanised iron tub" and I think you have a recoliless rifle?
Cheers
Chris
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ChrisGreaves
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Re: How’s my physics?

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viking33 wrote:Chris, I think only you would want to take the time, energy, wonderment and effort, to set up the rifle like you theorize and then ask why the bullet didn't fall right back into the gun barrel!
Well, Viking, thank you for the compliment! :thumbup:
This arose from an argument a discussion I won about explosions of warships a hundred years ago. The point was voiced that men on deck would die the instant they fell back on to the deck, and I claim that they would be dead before they left the deck, on account of the Kinetic energy that would have to be imparted to their bodies to lift them high enough to have the potential energy to be converted to kill them when they landed back on the deck.
That is, it is the initial blast of kinetic energy would turn their brains and bodies into jelly prior to the thirty-second flight.
From that my mind started narrowing down options. For example, what is the chance the (by now dead) body would return to the deck of the ship? To the exact spot.
The time is long gone when one is allowed to experiment with live seamen, so I thought of a bullet from a rifle.
I see now that I should have stayed at cannon-balls :sad:
Cheers
Chris
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ChrisGreaves
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Re: How’s my physics?

Post by ChrisGreaves »

The extra padding using the beret with the badge, ...
You guys are vicious, mean, and nasty.
I am ***so*** glad that I went to Mr. Puzey's physics classes instead of mooching off with the cadets.
:grin:
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AlanMiller
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Re: How’s my physics?

Post by AlanMiller »

ChrisGreaves wrote:In theory we are outside any Heisenberg sort of uncertainty, but almost certainly still within the realms of chaos theory.
At this stage I can contemplate some sort of probability distribution (which could be verified by sampling thousands of firings and landings) which ought, at least, to enable us to verify the calculations based on wind speed, altitude, temperature and so on.
That is, even the chaos can be reduced to a formula that would help us to verify the remainder of our formula.

So I am left with my original thoughts on atmospheric variables PLUS some sort of probability distribution based on "tumbling".
I can't possibly see how chaos theory comes into it (unless you forgot the smiley).
The biggest uncertainty for your scenario, I'm guessing, would be the unpredictability of the transonic flight I mentioned before.
Your repeated tests would give you some sort of circular error probability but I don't know how that would help you with your original problem.

Alan

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BobArch2
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Re: How’s my physics?

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ChrisGreaves wrote:
BobArch2 wrote:Embedding the rifle in rocks is not going to make for a smooth exit of the bullet when fired. ...
Not exactly.
Hi Bob.
I just said "embedded in rocks", but I sure didn't mean three fist--sized rocks.
.....
Cheers
Chris
How dare you bring the subject back on topic! We were having fun with recoil stories! :grin:
Regards,
Bob

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Re: How’s my physics?

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BobArch2 wrote:How dare you bring the subject back on topic! We were having fun with recoil stories! :grin:
:laugh: :laugh: :laugh: Segues via "recoil stones" through "recall stones" into "rocks in the head" ... :rofl:
Last edited by ChrisGreaves on 15 Aug 2017, 15:37, edited 1 time in total.
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Re: How’s my physics?

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AlanMiller wrote:The biggest uncertainty for your scenario, I'm guessing, would be the unpredictability of the transonic flight I mentioned before.
Your repeated tests would give you some sort of circular error probability but I don't know how that would help you with your original problem. Alan
Thanks Alan.
I think I shall have to pull in my horns a bit. When I suggested "rifle" I was thinking more along the lines of "Something simple I could set up to prove a point in a practical way".
I hadn't thought in terms of "trans-sonic" or "tumbling", and these are problems that arise with rifles.
The original thought came from a subsonic tumbling mass of jellied flesh, so perhaps I would have made a better start had I considered a low-velocity spherical and solid projectile.
I was reluctant to mention pulverized bodies of marine types, what with this being a family-oriented board and some of us not yet having had our dinner.
Time for lunch, here.
Cheers
Chris
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Re: How’s my physics?

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ChrisGreaves wrote:
PJ_in_FL wrote:... rotation of the earth and altitude of the rifle will need to be factored in. ...
Hi PJ.
Why should rotation of the earth be factored in?
The bullet and the rifle barrel have zero velocity relative to each other at the time of firing.
Whatever their latitude, they have the same speed relative to the surface of the earth, that is, zero.
I know it is sung that the earth rotates at nine hundred miles an hour at the equator, (and less as we near the poles), but whatever the speed (relative to what?), the rifle embedded in rocks, and the bullet traveling away from the barrel, start off, and should end up, with a velocity of zero relative each to the other.
Cheers
Chris
Consider the time and velocity of any object completing the circumnavigation of a point (e.g. center of the earth). At any point in time that object has an X and a Y component of it's velocity. Although the absolute scalar values appear to stay the same, the actual velocity has to be constantly changing as a result of acceleration due to gravity, thus the angular velocity is constantly changing, but for our purposes we'll keep to just the scalar value of "X" as it applies to two different objects, the rifle and the bullet.

As the radius of the circle increases, the "X" portion (with respect to the center point) of the velocity must also increase if the period of circumnavigation is to remain the same. Increase R by a factor of 2 and an object must travel twice as fast in the "X" scalar component of it's velocity to go around the circle in the same time. Thus as an object increases in altitude (radius) it's "X" component of it's velocity must increase to keep up with an object at a lower altitude.

Since the bullet's lateral or "X" velocity was the same as the rifle's when fired, but the bullet's altitude increased, it will "fall behind" the rifle as both circumnavigate the same point but at different altitudes.

Or I could be wrong, but I don't think so.
PJ in (usually sunny) FL

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AlanMiller
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Re: How’s my physics?

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PJ_in_FL wrote:Since the bullet's lateral or "X" velocity was the same as the rifle's when fired, but the bullet's altitude increased, it will "fall behind" the rifle as both circumnavigate the same point but at different altitudes.
Are you thinking of the Coriolis effect here?

Alan

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Re: How’s my physics?

Post by Leif »

PJ_in_FL wrote:Or I could be wrong, but I don't think so.
I think you're right, PJ. Which means it'll have to be done at either the North or South pole, and presumably during the appropriate summer months otherwise you wouldn't see the bullet plop back into the barrel.
Leif

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Re: How’s my physics?

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Leif wrote:I think you're right, PJ. Which means it'll have to be done at either the North or South pole, and presumably during the appropriate summer months otherwise you wouldn't see the bullet plop back into the barrel.
Or if Chris is a conscientious sniper, he will have all the appropriate data to compensate for his latitude, and place his drop bucket/target accordingly.

Alan

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Re: How’s my physics?

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PJ_in_FL wrote:... Since the bullet's lateral or "X" velocity was the same as the rifle's when fired, but the bullet's altitude increased, it will "fall behind" the rifle as both circumnavigate the same point but at different altitudes.
I have thought about this, and I believe that you are correct in that I should include the effect of the "falling behind" in velocity in the calculation along with the atmospheric conditions at various altitudes.
In the limit to zero, I can ignore that "x" component of the velocity when, for example, the bullet has enough explosive charge to lift it just a millimetre out of the barrel(1) before falling back in.
I can now visualize the bullet as being independent of the earth's surface velocity once it is released from the frictional attachment to the earth.
For as long as the bullet is inside the rifle barrel, it is part of the rifle, which is fixed to the earth. But once free of the barrel, the bullet continues Newton-like in a straight line until etc etc.
The surface of the earth, and hence the barrel, get dragged around and down as rotation of the earth continues.
:clapping: :cheers: :chocciebar: From Chris

(1)It took great feets of mental strength not to type "barely out of the barrel" at this point.
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Re: How’s my physics?

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AlanMiller wrote:Are you thinking of the Coriolis effect here? Alan
Interesting video, but I think it shows a different problem. The problem shown in the video is that of "missing a target" that is independent of the rifle (in the video's example "One thousand yards to the east/west").
I am looking at a situation where the source of the bullet (the rifle barrel) is the target, and so has no horizontal displacement east/west/north/south from the source & target.
That said, I still have to think a bit more.
As a human I find it difficult to remember that even while I am standing still on the face of the earth, I am describing an arc relative to some point in space fixed outside of the earth. I evolved as a Flatlander.

Now, I don't know how this happened, but about two hours after watching your referenced video clip I found myself here at the 0m31s mark and now have to make a note in my calendar for next December.

(signed) "YouTube addict" of Collingwood.
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Re: How’s my physics?

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ChrisGreaves wrote:Interesting video, but I think it shows a different problem. The problem shown in the video is that of "missing a target" that is independent of the rifle (in the video's example "One thousand yards to the east/west").
I am looking at a situation where the source of the bullet (the rifle barrel) is the target, and so has no horizontal displacement east/west/north/south from the source & target.
That said, I still have to think a bit more.
The issue is that the ground rotates beneath the bullet. Your vertical shot is just at the extreme of a (idealized) parabolic trajectory. The principle is the same.

Alan