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Longitudinal vibrations in solid metal rods

  1. Nov 20, 2009 #1
    Hi people,

    I have a question which i hope you helpful guys/gals can help to shed light on.

    We all know when we strike one end of a solid metal rod with a hammer sideways (i.e. from left to right), longitudinal vibrations will be set up across the length of the rod. Textbooks and websites always say that when we hold with our fingers in the centre of the rod, that location becomes a node.

    My question is why does our fingers introduce a node? Are our fingers so strong that we can force every metal atom to remain still and not vibrate to and fro? Sounds a bit far stretched to me...

    Thanks for the advice.
     
  2. jcsd
  3. Nov 20, 2009 #2
    Hi, vibrations discontinue and becomes like a sine wave..so you there will be a node something..sometimes force on figures also matter..for e.g. in string musical instrument..
     
  4. Nov 21, 2009 #3
    Hi Rajini,

    Thanks for the reply. But i guess it still doesnt address the question why the presence of the holding fingers force that location to become a node.

    Any other responses from the experienced forummers please?

    Thanks!
     
  5. Nov 23, 2009 #4
    Hi klng,
    when you hold at a point..you will minimize the amplitude of the vibration at that point..
    Node= zero amplitude and antinode=max. amplitude.
    Is that okay..
     
  6. Nov 23, 2009 #5
    As you point out, striking a solid metal rod on the end with an axial hammer hit will induce a longitudinal compression wave in the rod that will reflect at the ends and reflect back and forth from end to end. Holding the rod in the center will damp all transverse resonant modes that do not have a node in the center. However, holding the rod in the center won't (I think) convert a longitudinal wave into a transverse wave. The lowest resonant transverse mode is a half-wave with maximum transverse motion at the ends, and with a node in the center. The next is a 3/2-wave mode.
    Bob S
     
  7. Nov 24, 2009 #6
    Depends on the scenario. A long thin piece of metel - Yes - point of contact = node. But short strong piece of metel - No. Proof: hold a metel punch tool with your bare hands and hit it hard with a hammer!! OUCH!! It really hurts. The transverse forces go into your fingers.
     
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