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  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?
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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

    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.
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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

    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

    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


    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

    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

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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.

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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.
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    Re: Impact formula

    Quote Originally Posted by Willie B View Post
    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.
    The teacher was introducing basic concepts of kinematics in the face of gravity, without going into, or even knowing, the specifics of rifles and real-life ballistic projectile trajectories. The only thing wrong was her "scenario", because she didn't know the specifics of firearms/scopes/etc, and that was HER mistake, Not physics. Not "the book". Not even the teacher's underlying idea was incorrect. If your son is so smart, then he would have realized what the teacher was doing was INTRODUCING the basic underlying idea has to do with basic projectile trajectories analyzed in their independent x- and y-components. To say that the "oh the book was wrong, my son/daughter knows more" and/or "oh the teacher's wrong, my son/daughter know more than they do" what is wrong with some parents. Yes there are some bad teachers out there (I've worked with some), but the books are hardly ever wrong. Somehow the PhD physicists got it all wrong after all the studying that they did and knowledge acquisition they have come to have? Right. I would be very hard pressed to think that actual "scenario" was presented in a respected, published high-school level physics book. What is the ISBN of this physics book so I can look it up and read that problem as it was stated? Going from your elaborate response, it sounds like you just wanted to tout out what you knew about firearms to try and make the physics teacher look bad/incompetent. It's not hard to read between the lines.
    Last edited by Oscar; 06-09-2019 at 08:57 PM.
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    Re: Impact formula

    Quote Originally Posted by Oscar View Post
    The teacher was introducing basic concepts of kinematics in the face of gravity, without going into, or even knowing, the specifics of rifles and real-life ballistic projectile trajectories. The only thing wrong was her "scenario", because she didn't know the specifics of firearms/scopes/etc, and that was HER mistake, Not physics. Not "the book". Not even the teacher's underlying idea was incorrect. If your son is so smart, then he would have realized what the teacher was doing was INTRODUCING the basic underlying idea has to do with basic projectile trajectories analyzed in their independent x- and y-components. To say that the "oh the book was wrong, my son/daughter knows more" and/or "oh the teacher's wrong, my son/daughter know more than they do" what is wrong with some parents. Yes there are some bad teachers out there (I've worked with some), but the books are hardly ever wrong. Somehow the PhD physicists got it all wrong after all the studying that they did and knowledge acquisition they have come to have? Right. I would be very hard pressed to think that actual "scenario" was presented in a respected, published high-school level physics book. What is the ISBN of this physics book so I can look it up and read that problem as it was stated? Going from your elaborate response, it sounds like you just wanted to tout out what you knew about firearms to try and make the physics teacher look bad/incompetent. It's not hard to read between the lines.
    I actually had the same question twice when I went to college.
    I think you'll find that his textbook contains questions similar to below.

    First time it was an arrow aimed directly at the monkey. In other words, no arc for proper shot placement.
    In this slower scenario it's easier to visualize that gravity will affect both monkey and arrow over what ever time period it takes the arrow to get to the monkey.
    Other possible variables are also neglected in this simplistic style question.

    The second time it was a bullet. Also aimed directly with no arc for proper shot placement.
    The time is much shorter, but to the same end.
    Again, any other possible variables are neglected.

    An additional question, preceding the other two, was the classic:
    "Which bullet hits the ground first? One aimed parallel to the Earth, or one dropped at the same time as the other is fired."

    Now, in my opinion, this question has to neglect the curvature of the Earth to assume a bullet could be fired "parallel."

    The wording of the question is critical.

    It's very common for students to "read into" a question based on personal tangible experience, instead of taking the beginning fundamental questions at face value.

    This is where the teacher's pre-loading of the thought process is important. Students have to be made to understand that math/physics always starts with the fundamental style questions before adding in the complexity of additional variables.

    If the teacher does not do this, students can easily misunderstand what is being asked.
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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.
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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.
    Momentum isnt exactly a good measure of kinetic energy.... Its a good measure of energy exchange in collisions and braking time and stuff...

    Consider a strong man pushing a 50,000kg train car at 0.5 m/s (about 1.5ft/sec)
    Consider a car with mass 1000kg and speed 25m/s (55mph)

    It takes so little kinetic energy, maybe 300watts to push the train car that a person can do it.
    It takes nearly 70,000 watts of energy to run the vehicle at 55mph.

    The momentum of the train car is 25,000 units. KE = 10,000 Joules
    The momentum of the car is 25,000 units. KE = 625,000 Joules




    If the train car and the car crashed into each other face on (in an inelastic collision), they would cancel each other out, yet their kinetic energies are VASTLY DIFFERENT. A human being can push the train car, yet it takes a strong engine to push the car at that speed, yet in a collision, they cancel each other out. If you looked at Momentum and Kinetic Energy are completly different..... In these collisions, KE is not conserved.
    Last edited by n00b; 10-23-2019 at 06:49 PM.
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  23. #23
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    Re: Impact formula

    Quote Originally Posted by n00b View Post
    Momentum isnt exactly a good measure of kinetic energy.... Its a good measure of energy exchange in collisions and braking time and stuff...

    Consider a strong man pushing a 50,000kg train car at 0.5 m/s (about 1.5ft/sec)
    Consider a car with mass 1000kg and speed 25m/s (55mph)

    It takes so little kinetic energy, maybe 300watts to push the train car that a person can do it.
    It takes nearly 70,000 watts of energy to run the vehicle at 55mph.

    The momentum of the train car is 25,000 units. KE = 10,000 Joules
    The momentum of the car is 25,000 units. KE = 625,000 Joules




    If the train car and the car crashed into each other face on (in an inelastic collision), they would cancel each other out, yet their kinetic energies are VASTLY DIFFERENT. A human being can push the train car, yet it takes a strong engine to push the car at that speed, yet in a collision, they cancel each other out. If you looked at Momentum and Kinetic Energy are completly different..... In these collisions, KE is not conserved.
    A huge concept I will go to my grave never understanding.
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    Re: Impact formula

    Quote Originally Posted by n00b View Post
    Momentum isnt exactly a good measure of kinetic energy.... Its a good measure of energy exchange in collisions and braking time and stuff...

    Consider a strong man pushing a 50,000kg train car at 0.5 m/s (about 1.5ft/sec)
    Consider a car with mass 1000kg and speed 25m/s (55mph)

    It takes so little kinetic energy, maybe 300watts to push the train car that a person can do it.
    It takes nearly 70,000 watts of energy to run the vehicle at 55mph.

    The momentum of the train car is 25,000 units. KE = 10,000 Joules
    The momentum of the car is 25,000 units. KE = 625,000 Joules




    If the train car and the car crashed into each other face on (in an inelastic collision), they would cancel each other out, yet their kinetic energies are VASTLY DIFFERENT. A human being can push the train car, yet it takes a strong engine to push the car at that speed, yet in a collision, they cancel each other out. If you looked at Momentum and Kinetic Energy are completly different..... In these collisions, KE is not conserved.

    There are other variables involved though. Since there is no such thing as an inelastic collision it kind of makes the whole thing a bit unreal. There is a set of laws in our universe about, start change and stop. You cannot change an object without starting or stopping it both require time. When things are moving fast, time can mean an added destruction or force applied to an object because it is impossible to reverse an object's direction instantly. When you look at the hood of your car and see what the bugs have done to your paint that is the effect of start, change, and stop. When two objects are heading towards each other and stike each other there is going to be an elastic collision no matter what. Even the paint that is moving in one direction before it can change direction and absorb some impact has to stop, that is when the damage to the paint occurs. For that split second the paint is harder than glass and more brittle.

    That is why so much of the safety and accident information is flawed and just plain wrong, because they no longer take into consideration start, change and stop. There is no velocity no material that is not bound by start, change, and stop.

    Sincerely,

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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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