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Thread: Impact formula

  1. #1
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    Impact formula

    School me in the math of inertia.

    I lay 1 LB on the head of a nail nothing happens. If I swing a 1 LB hammer at a high rate of speed taking advantage of leverage to speed its travel I can effectively drive it with a few blows.

    A 180 grain bullet hits a gallon of paint at 500 FPS, it might not even leak. If it hits at 2000FPS, the can explodes.

    The Karate black belt smashes cement blocks with his bare hands, Or I can swing a short 2x6, hit it on a rock and break it in half.

    Old time wood splitters slammed the block at speed making them more effective at both splitting wood, and removing human limbs.

    How is this calculated?
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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    Re: Impact formula

    Oh Boy,Willie, I'm poppin' up some popcorn for this!! Sorry, I'm no help for you. I'm sure an Einstein or two will come along.
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    Re: Impact formula

    Great question and I've always wondered myself. I believe the force also has to be quantified in area applied, basically psi which would factor in hardness/surface at area of impact. I've also wondered what effect - if any - change of velocity at the time of impact has, ie would two identical blows except one is in the process of deceleration and one accelerating at impact at the same velocity strike with the same force?
    Last edited by SlowBlues; 06-02-2019 at 04:44 PM.

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    Re: Impact formula

    Hopefully somebody gives you the answer in english terms.... cause metric is just really gonna twist ya'

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    Re: Impact formula

    E= 1/2 m v^2.

    Edit to add "A 180 grain bullet hits a gallon of paint at 500 FPS, it might not even leak. If it hits at 2000FPS, the can explodes. "

    Going from 500 FPS to 2000 FPS raises the velocity 4 fold but raises the energy 16 fold because of the V^2.
    Last edited by FlaJoe; 06-02-2019 at 05:04 PM.

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    Re: Impact formula

    Simple enough, thanks Strike THROUGH your opponent, right?

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    Re: Impact formula

    "would two identical blows except one is in the process of deceleration and one accelerating at impact at the same velocity strike with the same force?"

    Yes, according to the laws of physics they would strike with the same energy. HOWEVER, for them to be accelerating or decelerating then there much be forces apply to them ( however from opposite directions) so depending on what is causing those forces they could add or subtract from the energy of the impact. For example, your arm applying force to the hammer to swing it would also add energy to the impact when the hammer hits the nail.

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    Re: Impact formula

    Quote Originally Posted by FlaJoe View Post
    E= 1/2 m v^2.

    Edit to add "A 180 grain bullet hits a gallon of paint at 500 FPS, it might not even leak. If it hits at 2000FPS, the can explodes. "

    Going from 500 FPS to 2000 FPS raises the velocity 4 fold but raises the energy 16 fold because of the V^2.
    I'm not sure I get it yet.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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    Re: Impact formula

    F=ma

    Where F = force

    m=mass

    a= acceleration

    You can increase force by increasing mass or acceleration. The pressure formula should also be looked at but I'm not sure I remember it at the moment. I think it's Pressure=force divided by area but you should verify.

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    Re: Impact formula

    I see doubling the weight, doubles the energy. Doubling the speed quadruples the energy.

    http://www.1728.org/energy.htm
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    Re: Impact formula

    Quote Originally Posted by Sandy View Post
    I see doubling the weight, doubles the energy. Doubling the speed quadruples the energy.

    http://www.1728.org/energy.htm
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    Re: Impact formula


    Willie B


    Quote Originally Posted by Willie B View Post
    School me in the math of inertia.

    I lay 1 LB on the head of a nail nothing happens . . .
    A 180 grain bullet hits a gallon of paint . . .
    The Karate black belt smashes cement blocks with his bare . . .
    Old time wood splitters slammed the block at speed making . . .

    How is this calculated?
    You have posed four distinct [disparant] inertial/mass queries -

    All four - incorporate human factors - which pollute Physical Math
    Formulations -

    An answer to any one of your postulations would be complicated.

    To answer all Four at Once would be tantamount to answering the
    Unified Field Theory . . .


    Opus

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    Re: Impact formula

    Short answer...


    In classical mechanics, kinetic energy (KE) is equal to half of an object's mass (1/2*m) multiplied by the velocity squared. For example, if a an object with a mass of 10 kg (m = 10 kg) is moving at a velocity of 5 meters per second (v = 5 m/s), the kinetic energy is equal to 125 Joules, or (1/2 * 10 kg) * 5 m/s2.

    Inertia is an intrinsic characteristic of the object related to its mass. Inertia tells you how much force it will take to cause a particular acceleration on the object. Momentum is a function of an object's mass and velocity. Momentum is a measure of the kinetic energy of the object.
    Last edited by Fast Leroy; 06-03-2019 at 09:53 AM.
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    Re: Impact formula

    Willie,

    Opus is correct, in that those 4 scenarios incorporate different kinematic calculations, and also involve engineering principles (regarding stresses/deflections/fractures) all at the same time. There is no "this", in your question as to "how is this calculated", as they are distinct enough to need their own systems of solutions. You would need several courses in physics and mechanical engineering to properly understand it all, and by "understand" I mean being able to set-up all the equations of motion and stresses/moments all completely on your own and solving them for the needed quantities. Pick up a (hefty) university-level physics book, and if you can solve all of the kinematic problems in it, you are well on your way to understanding the systems you described.
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    Re: Impact formula

    I am overwhelmed, stupefied. I imagined it could be reduced to pounds. V is not a concept I grasp. Been through Algebra I, II. With help from a couple of my sisters friends who were charitable, then a pact with a gay teacher who hated me (mutual), I passed. I apologize for the question. It was, and is, over my head.

    No, I don't hate gays. I did hate that teacher. His being gay, (flamboyantly gay), was a quick, easy explanation C. 1972.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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    Re: Impact formula

    Quote Originally Posted by Sandy View Post
    I see doubling the weight, doubles the energy. Doubling the speed quadruples the energy.
    THAT is the bit of info I have always remembered. All the formulas, I gradually forgot.

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    Re: Impact formula

    Where is Jackie Chan when we need him ?
    If you let me score the block a little I'll snap it for you.Even with my forehead. I promise I wont wear lipstick.

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    Re: Impact formula

    and to mess it up more why can a 16 lb sledge move a pin that a 20 ton press will not budge
    Do not argue with an idiot. He will drag you down to his level and beat you with experience.

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    Re: Impact formula

    Quote Originally Posted by Fast Leroy View Post
    Short answer...


    In classical mechanics, kinetic energy (KE) is equal to half of an object's mass (1/2*m) multiplied by the velocity squared. For example, if a an object with a mass of 10 kg (m = 10 kg) is moving at a velocity of 5 meters per second (v = 5 m/s), the kinetic energy is equal to 125 Joules, or (1/2 * 10 kg) * 5 m/s2.

    Inertia is an intrinsic characteristic of the object related to its mass. Inertia tells you how much force it will take to cause a particular acceleration on the object. Momentum is a function of an object's mass and velocity. Momentum is a measure of the kinetic energy of the object.
    Yeah, that was my first thought.

    Let's say...you drop an 8lb artillery shell on your foot...might break a toe. But that same shell travelling at 1100fps will go through a concrete wall.

    In simple terms that I can grasp....the energy you impart to the object during acceleration carries thru to the point of impact That initial energy has to be dissipated by the other object the shell strikes....causing great harm. Shell still only weighs 8lbs, but it's packin' the thousands of psi it took to get it moving out of that gun barrel.

    In a perfect cartoon world, the shell would run out of energy, and at the terminus, drop on yer foot, and break a toe. Still 8lbs worth of damage, but to a lesser degree.

    Or somethin' like that

  20. #20
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    Re: Impact formula

    Quote Originally Posted by Fast Leroy View Post
    Short answer...


    In classical mechanics, kinetic energy (KE) is equal to half of an object's mass (1/2*m) multiplied by the velocity squared. For example, if a an object with a mass of 10 kg (m = 10 kg) is moving at a velocity of 5 meters per second (v = 5 m/s), the kinetic energy is equal to 125 Joules, or (1/2 * 10 kg) * 5 m/s2.

    Inertia is an intrinsic characteristic of the object related to its mass. Inertia tells you how much force it will take to cause a particular acceleration on the object. Momentum is a function of an object's mass and velocity. Momentum is a measure of the kinetic energy of the object.
    Thank you Leroy.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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    Re: Impact formula

    Quote Originally Posted by farmersammm View Post
    Yeah, that was my first thought.

    Let's say...you drop an 8lb artillery shell on your foot...might break a toe. But that same shell travelling at 1100fps will go through a concrete wall.

    In simple terms that I can grasp....the energy you impart to the object during acceleration carries thru to the point of impact That initial energy has to be dissipated by the other object the shell strikes....causing great harm. Shell still only weighs 8lbs, but it's packin' the thousands of psi it took to get it moving out of that gun barrel.

    In a perfect cartoon world, the shell would run out of energy, and at the terminus, drop on yer foot, and break a toe. Still 8lbs worth of damage, but to a lesser degree.

    Or somethin' like that
    You could teach physics in my son's high school.
    At a parent conference the teacher (a burly, biker type) described her frustration with my son. She presented this scenario:
    A hunter wants to shoot a monkey hanging from a tree 100 yards away. He knows that the monkey will release its grasp at exactly the same time the bullet leaves the barrel of the rifle. Where does he need to aim?
    Zack answered: a bit lower than he wants to hit, the monkey will fall that far in the brief time the bullet takes to travel.
    Teacher assured him he was wrong. The bullet will fall at the same rate as the monkey. Aim at his heart.
    Zack tried to explain that the bore, and scope are not parallel. The barrel is deliberately pointed up in relation to the scope to compensate for gravity's effect on the bullet.
    Teacher dismissed that as ridiculous, "Nobody would do that"
    I was trying to pound it into this woman's head the student was right, book, and teacher were wrong. Mrs. B was getting upset, so I dropped the subject, and let this sanctimonious B**** go on thinking she was right.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  22. #22
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    Re: Impact formula

    Quote Originally Posted by Willie B View Post
    You could teach physics in my son's high school.
    At a parent conference the teacher (a burly, biker type) described her frustration with my son. She presented this scenario:
    A hunter wants to shoot a monkey hanging from a tree 100 yards away. He knows that the monkey will release its grasp at exactly the same time the bullet leaves the barrel of the rifle. Where does he need to aim?
    Zack answered: a bit lower than he wants to hit, the monkey will fall that far in the brief time the bullet takes to travel.
    Teacher assured him he was wrong. The bullet will fall at the same rate as the monkey. Aim at his heart.
    Zack tried to explain that the bore, and scope are not parallel. The barrel is deliberately pointed up in relation to the scope to compensate for gravity's effect on the bullet.
    Teacher dismissed that as ridiculous, "Nobody would do that"
    I was trying to pound it into this woman's head the student was right, book, and teacher were wrong. Mrs. B was getting upset, so I dropped the subject, and let this sanctimonious B**** go on thinking she was right.

    Both are rite in different ways: the bullet is still effected by gravity (32ft/second^2) so is the monkey so they will drop at the same rate. Kentucky windage compensates for Gravity and adjusts the barrel angle so that a stationary target not effected by gravity can be hit by the bullet that is effected by gravity. This scenario has been known since before I was born.

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    Re: Impact formula

    Quote Originally Posted by Insaneride View Post
    Both are rite in different ways: the bullet is still effected by gravity (32ft/second^2) so is the monkey so they will drop at the same rate. Kentucky windage compensates for Gravity and adjusts the barrel angle so that a stationary target not effected by gravity can be hit by the bullet that is effected by gravity. This scenario has been known since before I was born.
    Yes, and unless you were born in the 1800s A very long ti me before you were born.

    I'd bet the first cave man who ever threw a rock at a Wolly Mamoth figured that out.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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    Re: Impact formula

    Willie, mammoths don't fall from trees, they move horizontally. Your sons physics teacher was explaining gravity. Windage accounts for gravity provided you know the range. Your son saying that you lead the moving target applies to a target moving horizontally at hi speed. A bullet traveling at 2000fps is way faster than monkey falling at 32fps^2 . If the monkey is only 500 feet away from shooter then the bullet should only take 250 milliseconds to reach the monkey. The monkey barely moved at all but is falling at the same rate the bullet falls.

    I first heard that problem forty years ago but no monkeys falling, different approach .

    Which travels faster, a .22 or 45 caliber? The twenty two of course, that's why the twenty two travels further. They both hit the ground at the same time provided they were shot at the same time from same height and barrels level.

    Gravity is a weak but constant force. I forget what the speed needed for a rocket to escape Earths gravity is but, the faster a bullet travels, the farther it travels.


    Btw, a cavemans spear would travel faster than a rock so the Force would be more than a rocks and also has more pressure.

    Force equals mass times acceleration . Pressure equals Force divided by Area.
    Last edited by Insaneride; 06-07-2019 at 01:23 PM.

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    Re: Impact formula

    Willie, I stand corrected if my math is correct. In 250 milli seconds, an object or monkey wall fall 2 feet based on the speed of gravity.

    Gravity on Earth is 32ft/second squared. In a quarter second or 250 milli seconds the equation becomes

    32ft per 0.250seconds squared.

    32ft per 0.0625 = 2 feet. So, depending on the size of monkey, aim for his scrotum if you want a heart shot provided windage is set correctly for intended range.

    In my defense, that problem was posed differently when I first heard it. It didn't include monkeys the way I heard it.

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