Who knows their physics? Punching...
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Thread: Who knows their physics? Punching...

  1. Who knows their physics? Punching...

    Ok, going through some PPCT the other day with my SO and they brought up the concept of following through with a punch makes it more effective. I've heard this all my life and it brought me back to my physics class a few years back when we learned that the shorter the impact time of a collision, the greater the average force of that impact.

    F[average] = m * ([delta]V / [delta]T)

    So by following through with a punch you're increasing the time of the impact. What phenomenon is going on that makes following through more effective?


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  3. #2
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    Newton's first law I would assume... an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

  4. #3
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    I'm not sure about the equation you gave, or even if the average force > the peak force, but here is how I see it.

    Following through allows more energy to pass from the hand into the person. When someone pulls back, energy is lost not just from no longer making contact, but before that when muscle used energy to slow, stop, and retract the hand. Think about hitting a golf ball: If someone were to swing, but try and stop the head of the club right at the impact point, how much energy was used to slow and stop the club, that could have been used to strike the ball harder?

    From an anatomical standpoint, what causes internal damage is the organs tearing and hitting the wall of the body/bones in two ways (simplistically):

    1. Smashing someone's head against the sidewalk: The head hits the sidewalk and stops, the brain keeps moving and hits the inside of the skull, compressing (causes bruising, stretching, tearing, etc)

    2. Smashing a fist into someone's head: The fist hits the head which moves the skull back which hits the brain that is suspended in place (causes bruising, stretching, tearing, etc).

    Organs in the abdominal and thoracic cavity can tear (too much movement for the tissue) and bruise (depending on the organs hitting a hard surface) when these forces are enacted on the human body. In the 2nd case, I would think following through, would not only pass more energy into the body, but also move the body further creating more internal damage, which stops the threat faster.

    That's just my "educated guess" aka opinion...I'd like to see the answer based on your equation though.
    “One of the illusions of life is that the present hour is not the critical, decisive one.” – Ralph Waldo Emerson

  5. Quote Originally Posted by Firefighterchen View Post
    I'm not sure about the equation you gave, or even if the average force > the peak force, but here is how I see it.

    Following through allows more energy to pass from the hand into the person. When someone pulls back, energy is lost not just from no longer making contact, but before that when muscle used energy to slow, stop, and retract the hand. Think about hitting a golf ball: If someone were to swing, but try and stop the head of the club right at the impact point, how much energy was used to slow and stop the club, that could have been used to strike the ball harder?

    From an anatomical standpoint, what causes internal damage is the organs tearing and hitting the wall of the body/bones in two ways (simplistically):

    1. Smashing someone's head against the sidewalk: The head hits the sidewalk and stops, the brain keeps moving and hits the inside of the skull, compressing (causes bruising, stretching, tearing, etc)

    2. Smashing a fist into someone's head: The fist hits the head which moves the skull back which hits the brain that is suspended in place (causes bruising, stretching, tearing, etc).

    Organs in the abdominal and thoracic cavity can tear (too much movement for the tissue) and bruise (depending on the organs hitting a hard surface) when these forces are enacted on the human body. In the 2nd case, I would think following through, would not only pass more energy into the body, but also move the body further creating more internal damage, which stops the threat faster.

    That's just my "educated guess" aka opinion...I'd like to see the answer based on your equation though.
    I think you may have been on to the answer that I was thinking of. If it were possible to maintain full velocity until you made contact and then could immediately retract your hand, the average force would be maximized. But given that that is physically impossible, what we would are doing is having to slow down before impact is made which means that the change in velocity is much.


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  6. #5
    Quote Originally Posted by AndeyHall View Post
    Ok, going through some PPCT the other day with my SO and they brought up the concept of following through with a punch makes it more effective. I've heard this all my life and it brought me back to my physics class a few years back when we learned that the shorter the impact time of a collision, the greater the average force of that impact.

    F[average] = m * ([delta]V / [delta]T)

    So by following through with a punch you're increasing the time of the impact. What phenomenon is going on that makes following through more effective?


    Sent from my iPhone using Tapatalk
    The part of the equation you're neglecting to factor in is the amount of force behind that punch when it does connect. I recently (within the last couple of weeks) saw a show that was talking about the physics and bio-mechanics of a punch, and showed the musculature and motion of a strike, and exactly where a punch starts and finishes. It starts from the foot, using the leg muscles to carry power through the hips, which rotate adding more energy to the swing, and by the time you reach the fist, you have the momentum and energy of the entire body behind the hit, not just your arm strength as if you'd just swung starting from the shoulder or elbow.
    I'm sure you could find that on video on youtube. I don't recall what show I was watching.. probably something like modern warrior or something.. it was on when I turned on the TV.
    No statement should be believed because it is made by an authority.
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  7. #6
    I found it!!!!

    No statement should be believed because it is made by an authority.
    Robert A. Heinlein

  8. #7
    No statement should be believed because it is made by an authority.
    Robert A. Heinlein

  9. #8
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    Quote Originally Posted by AndeyHall View Post
    Ok, going through some PPCT the other day with my SO and they brought up the concept of following through with a punch makes it more effective. I've heard this all my life and it brought me back to my physics class a few years back when we learned that the shorter the impact time of a collision, the greater the average force of that impact.

    F[average] = m * ([delta]V / [delta]T)

    So by following through with a punch you're increasing the time of the impact. What phenomenon is going on that makes following through more effective?


    Sent from my iPhone using Tapatalk
    I teach high school physics and we dumb down what's happening so we don't have to bring calculus into a classroom that has a bunch of students who haven't had it. That equation, the impulse-momentum theorem states in words that given a constant net force the impulse (the net force times the time the force is exerted) will equal the change in momentum of the object receiving the force. Momentum is defined as the product of mass and velocity.

    A few factors are going on that makes this equation a little more complicated. Your initial assertion is that if you extend the time a force is in contact with an object, that object will accelerate (change its velocity) even more so. It's not constant. The thing is, the force you give starts out light and peaks to a high point and then starts to fall again. Think about punching someone and you will agree that the force is greatest somewhere in the middle of that punch. By riding through with the punch, you elongate the amount of time that the force you exert is near or about that peak area.

    If you jerk your punch back, like a jab, you never reach that peak force level AND you don't have much time in contact with the object that you are exerting that force.

    It is imperative that you follow through to get the maximum acceleration on the object you are striking. Acceleration, as I tell my students, is what hurts.

    There's a follow up to this though. The person getting hit isn't static. He can move. If he rides with your punch, he elongates the amount of time to stop your punch. The change in momentum of your fist is constant if you are trying to stop. Think about it this way, you have momentum with your fist and it will come to a stop. The change in that momentum is equal to the original momentum you had. Therefore, the force exerted on the person getting punched is lessened by extending the time you are punching him. This sounds like I've contradicted myself. I have not, I assure you. The first example is hitting someone who is not moving. This example is someone who is moving in the direction of your punch. It would make sense that if I was moving with your fist, the fist could never reach that peak level I mentioned earlier.
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  10. #9
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    Quote Originally Posted by wolf_fire View Post
    It is imperative that you follow through to get the maximum acceleration on the object you are striking. Acceleration, as I tell my students, is what hurts.
    Great post. This section is what I was getting at in my two explanations of how injury works.

    Abrupt deceleration or abrupt acceleration in a different direction (head/body hitting sidewalk, windshield, etc and immediately stopping or bouncing back) causing damage externally and internally (organs suspended keep moving until they tear, bruise, etc). Abrupt being your head stopping in 0.01 inches from full velocity in 0.1 seconds (hitting concrete), compared to stopping over 24 inches in 2 seconds (hitting a foam mat).

    Abrupt acceleration from a stop, causing the same injuries, or whiplash injuries. This movement is inversely related to stopping. If the hit is too slow, or doesn't have enough energy the object will move back too slowly to cause injury. The hit needs to move the head far enough (8 in vs 1 in) at a great enough speed (over 5 seconds vs over 0.5 seconds) to cause injury. Or if a body hit, or strike across the jaw, the acceleration has to be fast enough to reach or displace one body part before the entire body starts moving back.

    I feel the only way to achieve this movement is to follow through. It will take a lot of energy from one body to another to achieve the acceleration needed.



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    “One of the illusions of life is that the present hour is not the critical, decisive one.” – Ralph Waldo Emerson

  11. #10
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    Same for golf and baseball. follow-thru on the swing and the ball goes farther.
    GOD, GUNS and GUITARS

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