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Hammer and nails question

  1. Apr 4, 2004 #1
    Maybe some one can clear something up with what current theory is.

    If you take a hammer and you hit a solid object, how much time is involved in the transfer of energy from the hammer and or to the solid object?

    This is prompted by the dev. in another thread that questions the speed of Cause and effect.
    Last edited by a moderator: Apr 4, 2004
  2. jcsd
  3. Apr 4, 2004 #2
    Do we have to use QM? If so, we run up against Heisenberg's Uncertainity Principle. The minimum time that we can meaningfully discuss if QM is correct here is the Planck time, which is about 5.4 e-44 sec. Otherwise, the answer is, it depends!
  4. Apr 4, 2004 #3
    I definitely think it's "otherwise" :smile: .
  5. Apr 4, 2004 #4
    And I definitely think it "depends." So we're all in agreement! =]

  6. Apr 4, 2004 #5
    I think possible my question is a bit silly in that it's all about picking straws.....

    For energy to transfer it has to transfer yes?

    The start of transfer to the end of transfer. The start being the start and the end being the end.

    hmmmmm......Instantaneous start but a slower end maybe
  7. Apr 5, 2004 #6


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    Staff: Mentor

    This isn't all that hard to find out: pick a nail size and material, a hammer weight and speed and do the spring energy calculations. You can probably ignore the elasticity of the hammer, just model the nail as a spring.
    Last edited: Apr 5, 2004
  8. Apr 5, 2004 #7
    Are you saying that carpenters and brick masons can just ignore the effects of quantum mechanics and general relativity and still be able to do their job? LOL
  9. Apr 5, 2004 #8


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    The Uncertianty Principle! Now I understand. The motion of the hammer means we cannot know where it is! Thus it is imposible to hit a nail with a hammer!

    and I have experimental Proof! (Just look at anything I ever nailed) With a hammer of course!
  10. Apr 5, 2004 #9
    God doesn't play dice with my thumb, I get it every time.
  11. Apr 5, 2004 #10
    ha ha maybe I should have use a balloon instead of a nail.........
  12. Apr 5, 2004 #11
    russ waters said: "just model the nail as a spring."

    A spring? I would think this is nearly a perfectly inelastic collision. The hammer's kinetic energy goes to zero at which point the nail has been driven in some distance s, defined by:

    KE(hammer) = integral(dp/dt(hammer)*ds) - a (very small) increase in hammer's thermal energy
  13. Apr 5, 2004 #12
    Russ isn't as dumb as he looks. LOL. Russ doesn't miss much. Think about it. Russ is saying that the nail follows Hooke's law.
    Last edited by a moderator: Apr 5, 2004
  14. Apr 5, 2004 #13

    No greater than the speed of sound for the contact medium impacted.
    What occurs on impact is a "shock wave"
  15. Apr 5, 2004 #14


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    Staff: Mentor

    Well, actually, I guess it is more complicated: you have two things going on, not just one. I didn't take the thought all the way (lazy). The nail-hammer part is near perfectly elastic, the nail-board part is near perfectly inelastic.

    edit: reading the first post again, the author just says "an object" - so it could be just about anything. Elastic/inelastic will depend on the object. Either way though, its still not a difficult problem.
    Last edited: Apr 5, 2004
  16. Apr 5, 2004 #15
    Actually Russ, I was going to use the example of a block of iron say 10 cccm hittng a similar block of iron.

    The answer SEEMS obvious to me but I have been soooo wrong before which is why I ask it.....

    With out quoting some ones theories I would assume that energy is tranfered from one block to the other in full at the point of impact ( assuming the receiving object is held in a ridgid position as in non- movable)

    You know that little mobile with the balls on strings that clack clack away until gravity peels of all the inertia.

    One ball hits a row of say 5 other balls the ball on the opposite side reacts immediately the first ball hits.....is the assumption that I want to clear up

    Actually the Mobile of the balls is a good example of the fundamental I want to explore
    Last edited by a moderator: Apr 5, 2004
  17. Apr 5, 2004 #16
    You're right. I read the title of the thread and never stopped thinking about the object as a nail.
  18. Aug 15, 2010 #17
    I'd like to revive this thread for a practical purpose. I'm a tradesman with a hobby interest in science, and a most practical application for the original question.

    If you only look at the problem as 1/2 MV^2 the theory doesn't match the actual result. I was reading Wikipedia and they were discussing titanium hammers, and how the lighter head swings faster, making it easier to drive nails. I own a titanium hammer and a regular framing hammer. While the Ti hammer is OK for driving nails, if you need to move something heavy like a wall, it doesn't matter how fast you swing the hammer, the wall doesn't move.

    What I'm wondering right now is why is there a difference in the result between a heavy mass moving slowly compared to a light mass moving quickly even if the math says the force should be the same?

    Also, at really high impact speeds why is steel more brittle?
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