recoil v accuracy

[lightwind]

Why is it then that one's garden hose doesn't recoil until you squeeze the trigger on the nozzle and the water comes out?

Good question. The reason is that mass has to move (F=m*a) for there to be acceleration. If you have an empty water hose and start filling it up you can see it squirm around. That is mass moving through the hose. The mass moving has momentum and it passes it on to the hose. Your analogy of a hose and rifle is right if you have mass moving. If you have a closed nozzle on the end of your barrel and pull the trigger it would start things moving all over the place because there would be too much energy for the rifle. However, if you had a solid block of steel with a live round embedded in it (to be able to contain the force of the explosion without much motion) and detonated the round it would not move much at all and once the initial thump was done it would stationary until you relieved the pressure. The hose is the same way. If you turn the water on while you hold the hose you will feel the pressure build in it (if it is unpressurized to start). That little jump of the hose when the pressure turns on is an initial movement (hence momentum transfer).

The bottom line is conservation of momentum. If things are not moving they don't have momentum. A closed hose nozzle stops things from moving. When you turn it on they start moving again.

 

[RDM416]

Dwell Time And Your Trigger

As you can see, he says the rifle recoils about 0.25 to 0.375 inches before the bullet leaves the rifle.

Well, I am going to bow out of the physics side of the discussion. Without doing some research here I am just spinning my wheels, and I'm too lazy to dig into this any further.

HOWEVER.......... If the above quote were correct and our rifle barrels move .25 to .375 inches before the bullet left the barrel. We would never be able to hit anything at even 100 yards, much less 1000. I think I started this by saying "do the math" earlier, so I will again. .25 inch of movement at the muzzle would equal to how many MOA of error at 100???? Do the math.

 

[WildRose]

Just so that people are not confused by your comments:

Your comment: "The rocket does not accelerate until the forces contained are released."

No, that is not true. The rocket accelerates as the propellant is accelerated.

Obtuseness does not help the discussion. The propellent is the force contained within. Whether it is simple compressed gas being released by a valve, or the explosive epansion of the prpellent in the nozzle, the forces are being released creatin thrust.

Your comment: "The recoil does not begin, until the forces contained are released."

No, that is not true. No, it begins as the momentum of the bullet starts changing at the time of ignition.

Not to any significant degree which would affect accuracy.

 

[WildRose]

Good question. The reason is that mass has to move (F=m*a) for there to be acceleration. If you have an empty water hose and start filling it up you can see it squirm around. That is mass moving through the hose. The mass moving has momentum and it passes it on to the hose. Your analogy of a hose and rifle is right if you have mass moving. If you have a closed nozzle on the end of your barrel and pull the trigger it would start things moving all over the place because there would be too much energy for the rifle. However, if you had a solid block of steel with a live round embedded in it (to be able to contain the force of the explosion without much motion) and detonated the round it would not move much at all and once the initial thump was done it would stationary until you relieved the pressure. The hose is the same way. If you turn the water on while you hold the hose you will feel the pressure build in it (if it is unpressurized to start). That little jump of the hose when the pressure turns on is an initial movement (hence momentum transfer).

The bottom line is conservation of momentum. If things are not moving they don't have momentum. A closed hose nozzle stops things from moving. When you turn it on they start moving again.

Momentum begins when the force acting on an object exceeds the mass of the object being acted upon. Until that moment, there is no inertia, no movement, no momentum.

 

[WildRose]

Found some more good slow motion clips showing the recoil as the bullet leaves the barrel on several different weapons.

 

[lightwind]

WildRose:

You said: "Momentum begins when the force acting on an object exceeds the mass of the object being acted upon. Until that moment, there is no inertia, no movement, no momentum."

The answer is that Newton disproved this hundreds of years ago. You are confusing momentum with friction. When an object sits on a surface there is a minimum force that must be applied to move it because of the friction of the object with the surface. If an object is frictionless (in space) any amount of force will cause it to accelerate in accordance with F = m*a. Do you see any minimum amount is that familiar equation that says that you have to apply some force over some amount before an object will accelerate? If you do, I suggest that you might need a physics course. I have no doubt you can out shoot me. However, you do not understand Newton's laws of motion. Please show me how you figure that there is a need for a specific force to move an object. Newton showed that "an object in motion stays in motion" which was the knife in the heart of your basic assumption that there is a minimum force required to start an object into motion by showing that without friction a mass will keep its momentum until it is acted on by a force. That includes a situation where the object is at rest with respect to the observer applying the force. I will stop at Newton without trying to explain relative motion (which is why I mentioned the observer). If you have any idea why what I just pointed out is wrong, other than I can see it with my eyes in the video, please let me know.

 

[lightwind]

RDM416: You said: "HOWEVER.......... If the above quote were correct and our rifle barrels move .25 to .375 inches before the bullet left the barrel. We would never be able to hit anything at even 100 yards, much less 1000."

That quote was from someone who knows a lot more about guns than I do and was talking about trigger lock time. As for that translating into inaccuracy, only if the rifle is moving off its axis as it moves back. I agree that is a long distance, and when I saw it I had to think about it. However, the bullet is moving straight down the barrel so the initial force is directed away from the motion of the bullet. It is only after the stop for the rifle (our shoulders and skeletons) start to push against it that it can start moving in any direction other than straight back. Moving it straight back does not take it off target. The amount quotes is a large amount, but again, it came from someone who seems to be an expert. The straight motion is my interpretation of that but it could be wrong. I see the discussion as interesting.

 

[WildRose]

WildRose:

You said: "Momentum begins when the force acting on an object exceeds the mass of the object being acted upon. Until that moment, there is no inertia, no movement, no momentum."

The answer is that Newton disproved this hundreds of years ago. You are confusing momentum with friction. When an object sits on a surface there is a minimum force that must be applied to move it because of the friction of the object with the surface. If an object is frictionless (in space) any amount of force will cause it to accelerate in accordance with F = m*a. Do you see any minimum amount is that familiar equation that says that you have to apply some force over some amount before an object will accelerate? If you do, I suggest that you might need a physics course. I have no doubt you can out shoot me. However, you do not understand Newton's laws of motion. Please show me how you figure that there is a need for a specific force to move an object. Newton showed that "an object in motion stays in motion" which was the knife in the heart of your basic assumption that there is a minimum force required to start an object into motion by showing that without friction a mass will keep its momentum until it is acted on by a force. That includes a situation where the object is at rest with respect to the observer applying the force. I will stop at Newton without trying to explain relative motion (which is why I mentioned the observer). If you have any idea why what I just pointed out is wrong, other than I can see it with my eyes in the video, please let me know.

I don't teach physics but I did manage to pass all three physics courses I have taken.

A mass is not going to be moved from it's rest, until sufficient forces act upon it to overcome it's mass. With Momentum = MV an object at rest of any mass has a momentum of 0 because any number multiplied by 0=0.

The videos I provided show clearly that the recoil effect is not even perceptable until the bullet and expanding gasses leave the barrel.

We are talking about explosive forces contained within a pressure vessel here, not an object suspended in a vacuum in zero gravity.

According to the formula for calculating thrust (which is what we are dealing with) indeed in both horizontal and vertical systems there is a minimum amount of force required to put any amount of mass into motion.

http://www.msitec.com/pdf/thrust_calculations.pdf

Even using F=MxA in order to achieve acceleration of even 1m/s2 the force must at least be equal to the mass.

Physics Formulas: Laws of motion

In order to put a motionless object into motion, there IS a required minimum force to do so.

 

[lightwind]

OK, I have dropped to your level of believing a video. Take a look at this rifle and watch the vibration waves traveling up and down the barrel as well as the motion before the projectile leaves.

YouTube - ‪29426129's Channel‬‏

 

[WildRose]

OK, I have dropped to your level of believing a video. Take a look at this rifle and watch the vibration waves traveling up and down the barrel as well as the motion before the projectile leaves.

YouTube - ‪29426129's Channel‬‏

Vibration of the barrel is not recoil. It is harmonics.

 

[lightwind]

Yes, vibration is different from recoil. That is why I also told you to watch the motion when I should have said "linear motion." Can you see the rifle moving backwards before the projectile leaves the barrel?

Also, since you have taken three physics courses I assume the first one was mechanics (statics and dynamics). In the course you learned that forces add as vectors. The "F" you are using to say that you have to have a minimum to move anything is a composite force. It includes the force of the propellent, the force of friction (which adds in the opposite direction of the propellent force), the force of gravity, and the force of atmospheric pressure. Those all add to give you a net force less than the propellent force (which you mistake for a minimum force to move the mass). It is the force required to overcome friction and atmospheric pressure.

F(propellent) - F (friction) - F (atmosphere) +/- F(vector of gravity) = F(composite)

See if that makes sense or not.

 

[WildRose]

Yes, vibration is different from recoil. That is why I also told you to watch the motion when I should have said "linear motion." Can you see the rifle moving backwards before the projectile leaves the barrel?

It doesn't show what was happening at the trigger or shoulder. Thus there's no way to assume it's recoil particularly since it's an air rifle/pellet gun. It in fact appears to be due to the trigger pull or shooter "jerking". That camera angle does not however provide enough information to speak on it with any conviction either way.

Also, since you have taken three physics courses I assume the first one was mechanics (statics and dynamics). In the course you learned that forces add as vectors. The "F" you are using to say that you have to have a minimum to move anything is a composite force. It includes the force of the propellent, the force of friction (which adds in the opposite direction of the propellent force), the force of gravity, and the force of atmospheric pressure. Those all add to give you a net force less than the propellent force (which you mistake for a minimum force to move the mass). It is the force required to overcome friction and atmospheric pressure.

F(propellent) - F (friction) - F (atmosphere) +/- F(vector of gravity) = F(composite)

See if that makes sense or not.

None of which shows a force exerted driving the rifle backwards while the bullet and gases remain contained within the barrel. It would however explain the forces at work once the force/pressure is released from the end of the barrel, which does drive the rifle backwards due to the thrust.

Again, we are talking about the effects of an explosion in a closed pressure vessle which is vented only by the end of the barrel.

Until the bullet exits the barrel there is no action or force acting to drive the rifle backwards other than the miniscule amount of gas that escapes around and ahead of the bullett, as well as the barometric pressure on the exit side of the bullet.

Neither of which, nor a combination of the two contributes enough force to put the rifle in backward motion.

The force exerted by the explosion is equal in all directions inside of the pressure vessel.

Energy seeks the path of least resistance which is out of the end of the barrel, so the force moves in linear fashion out of the barrel behind the bullet.

I'm not a mathematician, nor am I a physicist, but I'm fairly well educated and spent much of the last 40 years blowing things up and shooting and trying to understand what made each work.

I however am apparently not as adept as would be required to explain this any more clearly.

 

[Buffalobob]

I'm not a mathematician, nor am I a physicist, but I'm fairly well educated

Go to Wiki and look up "recoiless rifle". You should have fired a few different varieties of these in your life. Notice what it takes to make them recoiless. For the true RRs, as opposed to rocket launchers, you will notice the break is on the rear.

The next time you are bored go to your local drinking water plant and look in the pump room. You will find thrust blocks everywhere. Even in closed systems, the fundamental laws of Newton must hold true and analyzing a rifle barrel as a closed loop is a weird way to deal with a simple problem.

 

[budlight]

OK, I have dropped to your level of believing a video. Take a look at this rifle and watch the vibration waves traveling up and down the barrel as well as the motion before the projectile leaves.

YouTube - ‪29426129's Channel‬‏

Lightwind, we are not going to win. Because we are talking to people that don't understand time, energy, motion, velocity, acceleration. They have closed minds. Just give up because no matter what is said they are set for life.

I had a person tell me once that the ocean tides are not caused by the moon. It was very simple to him. The moon is to far away for any gravity to pull a fluid like water which always returns like any fluid to it's natural level, water is not magnetic. He told me that it was wind and rotation of the earth. People came up with storm surges being a different animal and like me when I want to go surf casting or clamming I go get a tide chart. How can they print a tide chart in advance? None of that is proof to a closed mind.