Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Gaining power from pulling a punch?

  1. Nov 29, 2007 #1
    ok I have never taken a physics class in my life but I understand a lot about it from real world application. I am taking a wing chung doe martial arts class and they are saying that its the only form that is based on science however they seem to have some major flaws in there thinking however I dont know how to explain things to them right so here are my questions and please show me how I can prove to them what the answers are.

    #1 they say that if you punch a person and only penatrate 2 inchs and recoile (pull your punch back really fast) that you will have a lot more power in your punch becasue of the recoil and that this recoil will cause more damage to the person then if you would have fallowed through with the punch. the reason that they state this is because they say that if you continue to fallow through your mass will be joined with theirs and that your energy will not go into them but rather back into you. another thing they say is that if you fallow through your energy is not obsorbed into the body because they start moving backwards after the hit while with the 2 inch hit they dont move and all the punch energy stays in their body.

    so what can I do to prove them wrong? to me it is very simple however a lot of people are believeing what they say and that it is proven fact I believe it is totally fiction, I cant see how taking power away from a punch could in any way deliver more energy into the target.

    #2 from this 2 inch punch they say that a shockwave is created that could otherwise not be made if you did not recoile. how do I prove this wrong?

    I dont understand all the terms in physics so please explain things in words that avrage americans can understand it in. (The guys I will be explaining it to are not too smart)

    I love it when people say that they are the only one who uses sciencs and then they dont.

    Thanks for any help
  2. jcsd
  3. Nov 29, 2007 #2


    User Avatar
    Gold Member

    To what end? I mean, what do you think will be the outcome of this discussion with them?
  4. Nov 29, 2007 #3
    The reason I want to prove my point to them is because I am studying to be an instructor under them and I dont want to be teaching lies. I want to teach my students the truth and have the form respected because of how it works. anyone that hears them explain these things that understands physics at all will know that they are full of BS. however the masses will believe the lie because of their examples.

    They think things work for one reason but in reality its another. so they show an example as to how much more power their punch has by hitting you really fast but only going 1 inch deep then they hit you slow and go 5inchs and say see how much more the 1inch hurt see how much more power you have when you pull your punch back fast. the truth is that its their kinetic energy of the fast punch that had more power then the slow one however if they had punched at the same speed 5inches deep it would have hurt much much more.

    I am looking for some kind of example I can show them that any idot can understand because they are brain washed by their master.
  5. Nov 29, 2007 #4


    User Avatar
    Gold Member

    Right. My point is, how can you expect them to allow you to teach if you don't follow their principles.

    You are, of course right - they are full of hogwash - at least, as it has been explained. I would allow for the possibility that it is not the physics that is flawed but the explanation (usually by being dramatically oversimplified i.e. they may be giving you the answer they give any idiot who can't think through the physics). There's an outside possibility that a knowledgeable person can explain it in more detail such that it does follow known laws of physics.

    But more likely, it's just hogwash.

    Nonetheless, it seems to me that you have three choices here:
    - ask for further education in the physics area, either it will be vindicated, or you will find it's hogwash
    - suck it up and toe the party line
    - say thanks but see you later.

    IMO, the one option not open to you is to try to refute them.
  6. Nov 29, 2007 #5
    Thanks for your advice,
    I am quite sure that it is total BS and that they are explaining it right to me because I have asked and questioned them about this before. the founder of the style has explained it to me in person as well. I think that the style is good because the fast recoile puts you back in position for the next move its just that they lie to us and tell you that it gives you more power. the whole system is based on this fast recoil and the power it creates. I am going to make some exparments to prove my point to them and then expect to get kicked out. The only reason I am not just quitting is because some of my friends have been brainwashed by these guys and believe all there BS I want them to know the truth and hopfully they will either quit or get things chaged. We are being trained to open a school so if we all bann togeather then things might get changed but I doubt it. I am not totally sure if the guy who started the system is totally dumb or if he is just using this as a marketing scam pormissing that you will acheve more power then any other way if you use his systme...

    thanks again for all your help! I have learned a lot form this sight in the last two days.

  7. Nov 29, 2007 #6


    User Avatar
    Gold Member

    Huh. I had not thought of that but it soind like an excellent tactic. Any outstretched limb makes an excellent target for counter attack, as well as likely putting you off balance.

    Or they'll ridicule you. Worse, if you attempt a demonstration but don't really back it up convincingly, they may riducule you mercilessly.

    Well, good luck.

    I imagine it is the usual "plausibility" tactic. If you can describe something in a way that sounds right, it's good enough. It doesn't amtter whether it's true or not.
  8. Nov 29, 2007 #7


    User Avatar
    Science Advisor

    Sounds like they've watched one too many episodes of Kung Fu.

    I believe they are confusing the effective force "felt" by an object due to the objects momentum divided by contact time. Remember the old analogy of catching an egg without breaking it? If you allow enough time (by moving your hand away from the egg as it comes into contact with you) to absorb the momentum, the force you "feel" is less. Hence the egg doesn't crack.

    The problem with what they're telling you is if you are pulling the punch back, you are negating the force you are applying. So how could the other person feel more force by you reducing the force you're applying??

    Like Dave said, it's hogwash.
  9. Nov 29, 2007 #8
    physics for dummies?

    Thanks for the replies! Do any of you happen to have physics for dummies? maybe I can force them to read it oh wait maybe I ment common sense for dummies yea thats the one they need to read.

    So I was thinking about using a vat or big bag of water to demonstrate the shock waves created by each kind of strike. Sense the human body is 98% water I thought this would be as good of a demonstration as I can get witout using billistic gel. What do you guys thinK?

    Is there any other kind of demonstration I could do to prove my point? I was thinking about just hitting them really hard each way but I dont think they would like the outcome of that very much ha ha.

    Thanks again!
  10. Nov 29, 2007 #9
    Well, they may be right about their punch theory. All forces are diluted by the amount of time that they are applied. That's the idea behind bumpers and crumple zones in cars. The longer the force is applied, the less work is done, since work is Force / Time.

    I'm not sure about the shock wave part.
  11. Nov 29, 2007 #10
    What you said almost makes sense and I am sure that is how they came up with the idea in the first place but from my understanding it is false.

    In your example you are saying that because my full punch takes longer that it has less energy however that is not the case because my punch has exactly the same energy up to the two inch point at that point the time is exactly the same. after they start pulling back I keep driving through adding more energy into there body. does this make sense?

    Last edited: Nov 29, 2007
  12. Nov 29, 2007 #11
    Hmm... interesting...
    So would that mean that the theory if reducing the impact of car crashes is wrong?
    Or perhaps car crashes deal with only an instantaneous force instead of a continued one.

    Well, here's the problem. When you punch, you would be applying the same force, but a held-out punch would be for a longer time. While the kinetic energy would increase, the work done would decrease. That part I'm fairly sure about.
    However, I did come up with one possible reason - when a body is at rest, it receives the brunt of the force. However, after a prolonged force is applied, the force could then be converted into a horizontal velocity, or in this case, the person would be thrown to the side. That cushioning would weaken the force.
    However, you make an excellent point, and I am not so sure anymore.
  13. Nov 29, 2007 #12
    Just to elaborate on what stewartcs said, the way boxing teaches you to throw a punch is at a distance such that the punch connects when the arm is fully extended. Unlike retracting a punch, this method maximizes force and minimizes contact time. It's rarely that one performs a perfect punch, but the method is sound.

    As for a shockwave effect, I can honestly say I've never felt one myself though in training I've been punched often. So irregardless of the physics there, in practice I don't think any human will deliver enough force to cause any such effect to be noticably felt even if it does exist.
  14. Nov 29, 2007 #13


    User Avatar
    Gold Member

    Did you really just say 'irregardless'? :yuck:
  15. Nov 29, 2007 #14
    Who put the ir- in my word? I swear it wasn't me! o:)
  16. Nov 29, 2007 #15
    What a worthless post. :devil:
    [The above is a joke. Don't mean to offend anyone]

    I looked in the archives, and I found a very similar topic. Here is what is said, roughly a summary of the discussion, with general agreement.

    I like it. I get what I missed now - the W = F/T model assumes a single force applied at an instant. However, a punch is a force that is continually applied.

    I have seen the light.
  17. Nov 29, 2007 #16
    sorry about the worthless post. I just wantted to make sure that what I believe is really fact not fiction.

    thanks for all the responses

  18. Nov 30, 2007 #17
    so back to my question how do I prove my point to these people. if there is some confusion on this board then I am sure its going to be a bit hard to convence these people inless i have a really good explanation.
  19. Nov 30, 2007 #18


    User Avatar
    Science Advisor

    You could always punch them and follow through (make sure to really step into it), and then have them punch you and pull their punch like they say too. Keep it up until the first person gives in. I guarantee it won't be you.
  20. Nov 30, 2007 #19


    User Avatar
    Gold Member

    Set up a mechanical version. Swing a bat at an apple with a post in the way preventing follow-through. Swing the bat at an apple without the post. See which obliterates the apple more.
  21. Nov 30, 2007 #20
    The only problem is, the force of the apple on the post would be an extra reactionary force.
    Or is the post blocking just the bat?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook